SSL and HTTPS related ASP.NET Interview Questions
How do you provide Secure Communication over the world wide web?
Security is not just a matter of identifying users and preventing unauthorized users from accessing your Web applications, but it’s just as important to ensure that sensitive data sent across the Internet can’t be read by others.
To provide secure communication across the Internet, IIS supports a standardized means of encrypting and decrypting Web requests and responses. This cryptography requires that you request an encryption key called a server certificate from an independent third party called a certificate authority.
What is Secure Sockets Layer (SSL)?
The Secure Sockets Layer (SSL) is the standard means of ensuring that data sent over the Internet can’t be read by others. When a user requests a secure Web page, the server generates an encryption key for the user’s session and then encrypts the page’s data before sending a response. On the client side, the browser uses that same encryption key to decrypt the requested Web page and to encrypt new requests sent from that page.
Explain the process of secure communication using SSL?
Using SSL in your application requires special authorization from a recognized certificate authority. This authorization comes in the form of a server certificate, which you install in IIS to identify your server. The certificate authority licenses server certificates (for a fee) and acts as a clearinghouse to verify your server’s identity over the Internet.
When a user’s browser begins secure communications, it requests the server certificate and checks it against a list of trusted sites provided by the certificate authority. If the server certificate does not match one of the sites already authorized by the user, or if the server certificate does not match the Web address for which it was registered, or if there are any other problems with the server certificate, the browser displays a warning.
In this way, the certificate authority not only provides encryption for secure data transmission, but it also provides assurance to users that your Web site is authentic.
What is the largest certificate authority?
The largest certificate authority is VeriSign.
What are the steps to follow to use SSL in your Web application?
1. Generate a certificate request from IIS.
2. Request a certificate from a certificate authority.
3. Install the certificate on the server using IIS.
4. Install the certificate on browsers if you are using a test certificate.
5. Use the Secure Hypertext Transfer Protocol (HTTPS) when accessing secure pages in your application.
What should you do before you can request a server certificate from a certificate authority?
Before you can request a server certificate from a certificate authority, you must generate a certificate request from IIS. The certificate request contains encrypted information about your server that the certificate authority uses to identify your server over the Internet.
What are the steps to follow to generate a certificate request from the IIS?
1. Select Default Web Site in the console tree of the IIS, and then choose Properties from the Action menu. IIS displays the Default Web Site Properties dialog box.
2. Click the Directory Security tab in the Properties dialog box, and then click Server Certificate. IIS starts the Web Server Certificate Wizard.
3. Step through the wizard by reading each screen and clicking Next. The wizard instructions are straightforward.
4. When you click Finish at the end, the wizard creates an encrypted text file with the .cer file extension. That file is the certificate request that you send to the certificate authority.
Why do you have to select Default Web Site when generating a Certificate Request from IIS?
IIS requires that a certificate be created at the server root before secure communications can be created or configured for subordinate sites on the server. That’s why you have to select Default Web Site (or the root Web site if you have renamed it). After you have installed a server certificate at the root, you can repeat the process for subordinate sites if you want separate certificates for those sites.
What is the file extension of a server certificate?
.cer
What are the steps to follow to install the Certificate to enable SSL for your Web applications?
To install a server certificate in IIS:
1. Select Default Web Site in the console tree of the IIS snap-in, and then choose Properties from the Action menu. IIS displays the Default Web Site Properties dialog box.
2. Click the Directory Security tab in the Properties dialog box, and then click Server Certificate. IIS starts the Web Server Certificate Wizard.
3. Click Next, and select Process The Pending Request And Install The Certificate.
4. Click Next, and enter the name of the certificate file.
5. Click Next, and then click Finish to complete the installation.
What is the protocol on which secure pages are generally requested?
HTTPS, the protocol HTTPS is what initializes the secure communication. When you’ve begun secure communication, it continues until you specify a nonsecure site.
What are the steps to follow to make a web page secure in a web application?
To require secure communication for a Web page using IIS, follow these steps
1. Select the folder or file that requires secure communication, and then choose Properties from the Action menu. IIS displays the Properties dialog box.
2. Click the Directory Security tab, and then click Edit in the Secure Communications group. IIS displays the Secure Communications dialog box.
3. Select the Require Secure Channel (SSL) check box, and click OK.
Can a user access secure web page over HTTP protocol instead of HTTPS?
No, When you require secure communication for a Web page, that page can’t be viewed using HTTP. The user must type in or click a link using HTTPS, otherwise, access will be denied.
ASP.NET Interview Questions on Passport Authentication
What is Passport Authentication?
Passport authentication identifies users via Microsoft Passport’s single sign-on service. Microsoft Passport is meant to provide Internet users with a single identity that they can use to visit a wide variety of Web sites that require authentication. Information about the user is available to your application through a profile that is stored with Microsoft.
What are the advantages of Passport authentication?
The advantages of Passport authentication are that the user doesn’t have to remember separate user names and passwords for various Web sites and that the user can maintain his or her profile information in a single location. Passport authentication also provides access to other Microsoft services, such as Passport Express Purchase.
What is passport software development kit (passport SDK)?
To use Passport authentication in your Web application, you must install the Passport SDK. The Passport SDK is free for preproduction development and testing. To deploy a site for public use, you must obtain an annual license from Microsoft.
How does Passport authentication work?
When a user accesses an application that implements Passport authentication, ASP.NET checks the user’s machine for a current passport authentication cookie. If none is found, ASP.NET directs the user to a Passport sign-on page. Once the user signs in, the Passport service authenticates the user, stores an authentication cookie on the user’s computer, and directs the user back to the originally requested Web page.
What are the steps to follow to use Passport authentication?
1. Install the Passport SDK. Passport is not included with Visual Studio, although the .NET Framework does include classes for working with the Passport SDK once it is installed.
2. Set the application’s authentication mode to Passport in Web.config. Set authorization to deny unauthenticated users.
3. Use the PassportAuthentication_OnAuthenticate event to access the user’s Passport profile to identify and authorize the user.
4. Implement a sign-out procedure to remove Passport cookies from the user’s machine.
Where is PassportAuthentication_OnAuthenticate event present?
PassportAuthentication_OnAuthenticate event is present in Global.asax.
ASP.NET Interview Questions on Master Pages
What are Master Pages in ASP.NET? or What is a Master Page?
ASP.NET master pages allow you to create a consistent layout for the pages in your application. A single master page defines the look and feel and standard behavior that you want for all of the pages (or a group of pages) in your application. You can then create individual content pages that contain the content you want to display. When users request the content pages, they merge with the master page to produce output that combines the layout of the master page with the content from the content page.
What are the 2 important parts of a master page?
The following are the 2 important parts of a master page
1. The Master Page itself
2. One or more Content Pages
Can Master Pages be nested?
Yes, Master Pages be nested.
What is the file extension for a Master Page?
.master
How do you identify a Master Page?
The master page is identified by a special @ Master directive that replaces the @ Page directive that is used for ordinary .aspx pages.
Can a Master Page have more than one ContentPlaceHolder?
Yes, a Master Page can have more than one ContentPlaceHolder
What is a ContentPlaceHolder?
ContentPlaceHolder is a region where replaceable content will appear.
How do you bind a Content Page to a Master Page?
MasterPageFile attribute of a content page's @ Page directive is used to bind a Content Page to a Master Page.
Can the content page contain any other markup outside of the Content control?
No.
What are the advantages of using Master Pages?
1. They allow you to centralize the common functionality of your pages so that you can make updates in just one place.
2. They make it easy to create one set of controls and code and apply the results to a set of pages. For example, you can use controls on the master page to create a menu that applies to all pages.
3. They give you fine-grained control over the layout of the final page by allowing you to control how the placeholder controls are rendered.
4. They provide an object model that allows you to customize the master page from individual content pages.
What are the 3 levels at which content pages can be attached to Master Page?
At the page level - You can use a page directive in each content page to bind it to a master page
At the application level - By making a setting in the pages element of the application's configuration file (Web.config), you can specify that all ASP.NET pages (.aspx files) in the application automatically bind to a master page.
At the folder level - This strategy is like binding at the application level, except that you make the setting in a Web.config file in one folder only. The master-page bindings then apply to the ASP.NET pages in that folder.
What is @MasterType directive used for?
@MasterType directive is used to create a strongly typed reference to the master page.
Are controls on the master page accessible to content page code?
Yes, controls on the master page are accessible to content page code.
At what stage of page processing master page and content page are merged?
During the initialization stage of page processing, master page and content page are merged.
Can you dynaimically assign a Master Page?
Yes, you can assign a master page dynamically during the PreInit stage using the Page class MasterPageFile property as shown in the code sample below.
void Page_PreInit(Object sender, EventArgs e)
{
this.MasterPageFile = "~/MasterPage.master";
}
Can you access non public properties and non public methods of a master page inside a content page?
No, the properties and methods of a master page must be public in order to access them on the content page.
From the content page code how can you reference a control on the master page?
Use the FindControl() method as shown in the code sample below.
void Page_Load()
{
// Gets a reference to a TextBox control inside
// a ContentPlaceHolder
ContentPlaceHolder ContPlaceHldr = (ContentPlaceHolder)Master.FindControl ("ContentPlaceHolder1");
if(ContPlaceHldr != null)
{
TextBox TxtBox = (TextBox)ContPlaceHldr.FindControl("TextBox1");
if(TxtBox != null)
{
TxtBox.Text = "TextBox Present!";
}
}
// Gets a reference to a Label control that not in
// a ContentPlaceHolder
Label Lbl = (Label)Master.FindControl("Label1");
if(Lbl != null)
{
Lbl.Text = "Lable Present";
}
}
Can you access controls on the Master Page without using FindControl() method?
Yes, by casting the Master to your MasterPage as shown in the below code sample.
protected void Page_Load(object sender, EventArgs e)
{
MyMasterPage MMP = this.Master;
MMP.MyTextBox.Text = "Text Box Found";
}
Application build related ASP.NET interview questions
What are the 2 build options for an ASP.NET web application?
1. Debug
2. Release
What are the 3 levels at which we can have a configuration file for an ASP.NET web application?
1. At the web server level : The Machine.config file located in the Windows\Microsoft.NET\Framework\version\config directory. This sets the base configuration for all .NET assemblies running on the server.
2. At the application or web site level : The Web.config file located in the IIS root directory.This sets the base configuration for all Web applications and overrides settings in Machine.config.
3. In the sub directory of an application root folder : These settings override the settings in the root folder's web.config file.
What happens when you make changes to an application’s Web.config file?
When you make changes to an application’s Web.config file, IIS automatically restarts the application and applies the changes. This has the side effect of resetting current Application or Session state variables, which can adversely affect users.
What happens when you access the Web.config file from a browser?
For security reasons, you can’t access the Web.config file from a browser. If a user requests the Web.config file from your Web site, he or she will receive an "This type of page is not served" error message.
What happens when you access the Global.asax file from a browser?
For security reasons, you can’t access the Global.asax file from a browser. If a user requests the Global.asax file from your Web site, he or she will receive an "This type of page is not served" error message.
What are the steps to follow to host a web application on a web server?
1. Use IIS to set up a virtual folder for the application.
2. Copy the Web application to the virtual directory.
3. Add any shared .NET components to the server’s global assembly cache (GAC).
4. Set the security permissions on the server to allow the application to access required resources.
What are the 2 components that should be installed on a web server where, the ASP.NET web application runs?
ASP.NET Web applications run under IIS, so both IIS and the Microsoft .NET Framework must be installed on the server before that server can host Web applications.
What is the purpose of default start page in IIS?
A default page enables IIS to display a page if the user does not specify one in his or her request. For example, a user might make a request using only your domain name, such as http://www.sirymedia.blogspot.com/. If a default page is enabled, IIS will respond with http://www.sirymedia.blogspot.com/default.aspx.
Don’t confuse IIS default pages with the Web Forms application start page in Visual Studio .NET. Visual Studio .NET requires that you set a start page for each project so that the development environment knows which page to display first during debugging. This setting has no effect on the IIS default page settings.
How do you copy the COM component to the server and register?
COM components generally provide a setup program to install or remove them from the system. If the component doesn’t provide a setup program, you can copy it to the server and register it using the MFC RegSvr32.exe utility, as shown below:
RegSvr32 MyComname.dll
What is GAC?
GAC stands for Global Assembly Cache. The global assembly cache (GAC) is a special subfolder within the Windows folder that stores the shared .NET components.
What is the difference between weak-named .NET components and strong-named .NET components?
This difference is how the names are stored within the assembly. Weak names are not guaranteed to be unique and thus cannot be shared without potentially causing conflicts. Strong names are digitally signed and provide a public key that ensures there are no conflicts. Furthermore, .NET components with strong names can’t call unmanaged code (such as COM components) and thus avoid potential conflicts with dependencies.
Weak-named .NET components must be individually copied to the /bin directories of the Web applications where they are used. Strong-named .NET components can be copied into the server’s GAC
What is the account under which the ASP.NET worker process run?
By default, the ASP.NET worker process runs using the ASPNET account, which is created when you install the .NET Framework. This account has limited privileges, which can cause permission-denied errors if your application writes files or tries to read files outside the current Web application’s boundaries.
What are the 3 ways in which you can modify the additional permissions required by your application.?
1. Grant the ASPNET user access to the required files. To use this option, the server must be using the Windows NT file system (NTFS).
2. Change the group the ASPNET user belongs to.
3. Use impersonation to run the process as another user.
Why is it not a good idea to add ASPNET user to the Administrators group?
Adding the ASPNET user to the Administrators group gives your Web application full privileges on the server; however, it also poses a potential security risk because outside users might be able to manipulate your application to hack your server.
How do you impersonate the ASP.NET worker process?To use impersonation to run the ASP.NET worker process as a user other than ASPNET, set the identity element’s impersonation attribute in the application’s Web.config file.
Interview Questions on Query Strings in ASP.NET
Give an example of using querystrings to send data from one page to another?
Query strings are a very simple and popular technique to pass data from one Web page to the next. You send data as part of the URL. In the below example FName and LName are sent as part of the URL. In the page load of QueryStrings2.aspx we use Request.QueryString to read the values. As we are sending more than one query string we use the & symbol to seperate query strings.//Code to send query strings FName and LName as part of the URLQueryStrings2.aspx?FName=David&LName=Boon protected void Page_Load(object sender, EventArgs e)
{
//Code to read Query String values
string FirstName = Request.QueryString["FName"];
string LastName = Request.QueryString["LName"];
Response.Write("Data from QueryStrings1.aspx : " + FirstName + ", " + LastName);
}
Give an example to send Query Strings from code?
You can send query strings from server side code using the Response.Redirect() method as shown below.Response.Redirect("QueryStrings2.aspx?FName=David&LName=Boon");
What are the advantages of using Query Strings?
1. Query strings are easy to implement.
2. Browser support for passing values in a query string is nearly universal.
3. Query strings are contained in the HTTP request for a specific URL and do not require server resources.
What are the disadvantages of using querystrings to send data from one page to another?
1. Query strings are insecure because the information in the query string is directly visible to the user on the address line in the browser.
2. Many browsers impose a 255 URL character limit which can limit their flexibility.
Interview Questions on ASP.NET Page navigation techniques
What are different page navigation techniques in ASP.NET?
Hyperlink control : Navigate to another page.
Response.Redirect : Navigate to another page from code. This is equivalent to clicking a hyperlink.
Server.Transfer : End the current Web form and begin executing a new Web form. This method works only when navigating to a Web Forms page (.aspx).
Server.Execute : Begin executing a new Web form while still displaying the current Web form. The contents of both forms are combined. This method works only when navigating to a Web Forms page (.aspx).
Window.Open script method : Display a page in a new browser window on the client.
What is the difference between Response.Redirect and Server.Transfer?
1. When we use Server.Transfer the redirection happens on the server where as when we use Response.Redirect the redirection happens from the browser.
2. Server.Transfer is faster as there is no round trip involved while navigating from one webform to another webform.Response.Redirect is slower than Server.Transfer as there is round trip from the server to the client browser.
3. Server.Transfer works only with .aspx files where as Response.Redirect works with .aspx and .Htm pages.
4. Server.Transfer will work with files on the same web server. You can't use Server.Transfer to send the user to an external site where as Response.Redirect can do that.
5. Server.Transfer does not update the URL in the browser. For example when you navigate from WebForm1.aspx to WebForm2.aspx using Server.Transfer the URL in the browser still shows WebForm1.aspx while you are actually looking at WebForm2.aspx. Response.Redirect updates the URL in the browser.
What is the use of Server.Execute method?
Server.Execute method is used to process a second Web form without leaving the first Web form. This technique lets you direct the results from a Web form to a region on the current page.
Is it possible to send a webform's QueryString, ViewState, and event procedure information to another webform?
Yes, we can use Server.Transfer or Server.Execute to send a webform's QueryString, ViewState, and event procedure information to another webform.
For this to work you have to set the preserveForm argument to True.To be able to read one Web form’s ViewState from another, you must first set the EnableViewStateMac attribute in the Web form’s Page directive to False. By default, ASP.NET hashes ViewState information, and setting this attribute to False disables that hashing so that the information can be read on the subsequent Web form.
Interview Questions on cascading style sheets
What are the 2 ways provided by ASP.NET to format output in a Web application?
1. Use cascading style sheets (CSS) to control the appearance of elements on a Web form.These styles can set the color, size, font, and behavior of the HTML elements on a Web page.
2. Use Extensible Stylesheet Language Transformations (XSLT) to convert information from an Extensible Markup Language (XML) file to HTML output and position that information on a Web form. XSLT puts data from the XML file into HTML elements and applies styles to those elements.
What are Cascading style sheets?
Cascading style sheets (CSS) collect and organize all of the formatting information applied to HTML elements on a Web form. Because they keep this information in a single location, style sheets make it easy to adjust the appearance of Web applications.
What are the 3 levels at which formatting can be applied with in a web application?
1. Styles can be defined in a style sheet file. Styles in a style sheet can be applied to all webforms referencing the style sheet.
2. You can also define styles in the page’s head element. These styles can be applied to all elements on the current page.
3. You can also define styles inline, in the HTML tag itself. Inline styles are applicable only to the HTML element in which these styles are defined.
Inline formatting takes precedence over local formatting, which, in turn, takes precedence over global formatting. These precedence rules are the reason style sheets are referred to as cascading.
What are the advantages of storing style definitions in a style sheet file (.css) rather than locally in each Web form or inline with each HTML element?
1. Formatting can be maintained in one location so that you make changes only once for an entire application.
2. Several sets of parallel formatting rules can be maintained in separate style sheets for formatting output on different devices or for different user needs. For example, an application might provide standard, enlarged-type, and printer-friendly style sheets that the user can select at run time.
3. In general, you should use page and inline styles only when you have a really good reason to override the global styles. Relying heavily on page and inline styles can make it difficult to maintain the formatting in a Web application.
What HTML element is used to reference a style sheet on webform?
To reference a style sheet on webform you must add a link element to the page’s head element, as shown below.<link href="Styles.css" type="text/css" rel="stylesheet">
What is the use of Style Builder?
Style Builder is used to change the appearance of any of the styles in a style sheet. Changes to the style sheet change the appearance of all Web forms that reference that style sheet.
How do you modify a style sheet using style builder?
To modify a style sheet using style builder, follow these steps:
1. Open the style sheet in Visual Studio. Visual Studio .NET displays the style definitions in the Document window and an outline of the style sheet in the Tool window
2. Select the style to modify from the Tool window. Visual Studio .NET displays the definition for that style in the Document window.
3. Right-click in the style definition or right-click the style in the Tool window, and select Build Style from the shortcut menu. Visual Studio .NET displays the Style Builder Wizard.
4. Use the Style Builder to compose the formatting that you want to add or modify in the selected style, and then click OK.
5. When you have finished, you’ll see that the Style Builder adds the new or modified style attributes to the style definition.
Can you apply styles using class names or element IDs?
Yes, Using class names allows you to apply a single style to a number of different elements or to style the same element differently, depending on how the element is used. Using element IDs allows you to apply a style to a unique element on one or more Web forms.
When you create a style rule for a class, Visual Studio .NET adds a style definition to the style sheet using a .classnameidentifier.
You apply the style class to HTML elements by using the class attribute. You apply the style to server controls by using theCssClass attribute.
Can you change style sheets at run time?
Yes.
Interview Questions on cascading style sheets
What are the 2 ways provided by ASP.NET to format output in a Web application?
1. Use cascading style sheets (CSS) to control the appearance of elements on a Web form.These styles can set the color, size, font, and behavior of the HTML elements on a Web page.
2. Use Extensible Stylesheet Language Transformations (XSLT) to convert information from an Extensible Markup Language (XML) file to HTML output and position that information on a Web form. XSLT puts data from the XML file into HTML elements and applies styles to those elements.
What are Cascading style sheets?
Cascading style sheets (CSS) collect and organize all of the formatting information applied to HTML elements on a Web form. Because they keep this information in a single location, style sheets make it easy to adjust the appearance of Web applications.
What are the 3 levels at which formatting can be applied with in a web application?
1. Styles can be defined in a style sheet file. Styles in a style sheet can be applied to all webforms referencing the style sheet.
2. You can also define styles in the page’s head element. These styles can be applied to all elements on the current page.
3. You can also define styles inline, in the HTML tag itself. Inline styles are applicable only to the HTML element in which these styles are defined.
Inline formatting takes precedence over local formatting, which, in turn, takes precedence over global formatting. These precedence rules are the reason style sheets are referred to as cascading.
What are the advantages of storing style definitions in a style sheet file (.css) rather than locally in each Web form or inline with each HTML element?
1. Formatting can be maintained in one location so that you make changes only once for an entire application.
2. Several sets of parallel formatting rules can be maintained in separate style sheets for formatting output on different devices or for different user needs. For example, an application might provide standard, enlarged-type, and printer-friendly style sheets that the user can select at run time.
3. In general, you should use page and inline styles only when you have a really good reason to override the global styles. Relying heavily on page and inline styles can make it difficult to maintain the formatting in a Web application.
What HTML element is used to reference a style sheet on webform?
To reference a style sheet on webform you must add a link element to the page’s head element, as shown below.<link href="Styles.css" type="text/css" rel="stylesheet">
What is the use of Style Builder?
Style Builder is used to change the appearance of any of the styles in a style sheet. Changes to the style sheet change the appearance of all Web forms that reference that style sheet.
How do you modify a style sheet using style builder?
To modify a style sheet using style builder, follow these steps:
1. Open the style sheet in Visual Studio. Visual Studio .NET displays the style definitions in the Document window and an outline of the style sheet in the Tool window
2. Select the style to modify from the Tool window. Visual Studio .NET displays the definition for that style in the Document window.
3. Right-click in the style definition or right-click the style in the Tool window, and select Build Style from the shortcut menu. Visual Studio .NET displays the Style Builder Wizard.
4. Use the Style Builder to compose the formatting that you want to add or modify in the selected style, and then click OK.
5. When you have finished, you’ll see that the Style Builder adds the new or modified style attributes to the style definition.
Can you apply styles using class names or element IDs?
Yes, Using class names allows you to apply a single style to a number of different elements or to style the same element differently, depending on how the element is used. Using element IDs allows you to apply a style to a unique element on one or more Web forms.
When you create a style rule for a class, Visual Studio .NET adds a style definition to the style sheet using a .classnameidentifier.
You apply the style class to HTML elements by using the class attribute. You apply the style to server controls by using theCssClass attribute.Can you change style sheets at run time?Yes.
Interview Questions on ASP.NET Custom Controls
What are composite custom controls?
Composite custom controls combine one or more server or HTML controls within a single control class, which can be compiled along with other control classes to create an assembly (.dll) that contains a custom control library. Once created, the custom control library can be loaded into Visual Studio .NET and used in the same way as the standard server and HTML controls.
Composite custom controls are functionally similar to user controls, but they reside in their own assemblies, so you can share the same control among multiple projects without having to copy the control to each project, as you must do with user controls. However, composite controls are somewhat more difficult to create because you can’t draw them visually using the Visual Studio .NET Designer.
What are the steps to follow create and use a custom control in a Web application?
1. Create a solution containing a custom control project.
2. Add a Web application project to the solution, and set it as the startup project. You will use the Web application project to test the custom control during development.
3. Add a project reference from the Web application to the custom control project, and add an HTML @Register directive and control element to use the custom control on a Web form.
4. Create the custom control’s visual interface by adding existing controls to it through the custom control’s CreateChildControls method.
5. Add the properties, methods, and events that the custom control provides.
6. Build and test the custom control.
In general what is the base class for every composite custom control?
System.Web.UI.WebControls.WebControl
Which directive is used to add a custom control to a Web form?
Register directive.
What are the 3 Register directive's attributes?
TagPrefix
This name identifies the group that the user control belongs to. For example, the tag prefix for ASP.NET server controls is “asp”. You use this prefix to create a naming convention to organize your custom controls.
Namespace
This is the project name and namespace within the custom control assembly that contains the controls to register. Microsoft Visual Basic .NET uses the project name as an implicit namespace, so for controls written in Visual Basic .NET, use the project name.
Assembly
This is the name of the assembly (.dll) containing the custom controls. The control assembly must be referenced by the Web application. Referencing the assembly maintains a copy of it in the Web application’s /bin directory.
What are the differences between User Controls and Custom Controls?
1. User Controls are easy to create where as Custom Controls are difficult to create.
2. User Controls cannot be compiled into an assembly, where as Custom Controls can be compiled into an assembly.
3. User Controls cannot be added to tool box, where as Custom controls can be added to the toolbox.
4. You need to have a copy of user control in every project where you want to use it, where as this is not the case with custom controls. You can install a single copy of the Web custom control in the global assembly cache and share it between applications, which makes maintenance easier.
5. User controls are used for reusing existing user interface elements and code, but are not useful for developing reusable components for multiple web applications.
ASP.NET Interview Questions on web user controls
What are ASP.NET Custom controls?
Custom controls extend the tools available to Web developers. Using custom controls, you can encapsulate key aspects of the visual interface and program logic that you want to reuse throughout your application, or throughout your organization.
What are the 3 types of custom controls in ASP.NET?
Microsoft Visual Studio .NET provides three types of custom control for use on Web forms.
1. Web user controls
These combine existing server and HTML controls by using the Visual Studio .NET Designer to create functional units that encapsulate some aspect of the user interface. User controls reside in content files, which must be included in the project in which the controls are used.
2. Composite custom controls
These create new controls from existing server and HTML controls. Although similar to user controls, composite controls are created in code rather than visually, and therefore they can be compiled into an assembly (.dll), which can be shared between multiple applications and used from the Toolbox in Visual Studio .NET.
3. Rendered custom controls
These create entirely new controls by rendering HTML directly rather than using composition. These controls are compiled and can be used from the Toolbox, just like composite controls, but you must write extra code to handle tasks that are performed automatically in composite controls.
What are the limitations of user controls in ASP.NET?
As the user controls are not compiled into assemblies, they have the following limitations:
1. A copy of the control must exist in each Web application project in which the control is used.
2. User controls can’t be loaded in the Visual Studio .NET Toolbox; instead, you must create them by dragging the control from Solution Explorer to the Web form.
3. User control code is initialized after the Web form loads, which means that user control property values are not updated until after the Web form’s Load event.
What are the steps to follow for creating and using a user control in a Web application?
1. Add a Web user control page (.ascx) to your project.
2. Draw the visual interface of the control in the designer.
3. Write code to create the control’s properties, methods, and events.
4. Use the control on a Web form by dragging it from Solution Explorer to the Web form on which you want to include it.
5. Use the control from a Web form’s code by declaring the control at the module level and then using the control’s methods, properties, and events as needed within the Web form.
How do you identify user controls?
User controls are identified by their .ascx file extensions.
What is the base class from which user controls derive?
User controls derive from System.Web.UI.UserControl base class. This base class provides the base set of properties and methods you use to create the control.
What are the steps to follow to create properties and methods for the user control that you can use from a Web form?
To create properties and methods for the user control that you can use from a Web form, follow these steps:
1. Create the public property or method that you want to make available on the containing Web form.
2. Write code to respond to events that occur for the controls contained within the user control. These event procedures do the bulk of the work for the user control.
3. If the property or method needs to retain a setting between page displays, write code to save and restore settings from the control’s ViewState.
What happens when you drag a user control from solution explorer and drop it on a web form?
When you drag a user control from solution explorer and drop it on a web form, Visual Studio .NET generates a @Register directive and HTML tags to create the control on the Web form.
ASP.NET Interview Questions on web farm and web garden
What does the term Scalability mean?
Web applications that serve a large number of users or that present large amounts of data need to able to add capacity as users’ demands increase. The ability to add capacity to an application is called scalability. ASP.NET Web applications support this concept through their ability to run in multiple processes and to have those processes distributed across multiple CPUs and/or multiple servers.
What is the difference between a web farm and a web garden?
A Web application running on a single server that has multiple CPUs is called a Web garden in the ASP.NET documentation. A Web application running on multiple servers is called a Web farm.
If your web server has multiple processors, how can you specify that ASP.NET runs on all or some of the CPUs?
If your server has multiple processors, you can specify that ASP.NET runs on all or some of the CPUs by setting the webGardenattribute of the processModel element in the server’s Machine.config file
What are the implications on Application and Session state variables in a web farm or a web garden?
In both a Web garden and a Web farm, client requests are directed to the ASP.NET process that is currently least busy. That means that a single client can interact with different CPUs or servers over the course of his or her session. This has the following implications for Application and Session state variables:
Application state variables are unique to each separate instance of the Web application.
Clients can share information through Application state if the Web application is running on a Web garden or a Web farm.
Session state variables are stored in-process by default.
To enable Session state in a Web garden or Web farm, you need to specify a Session state provider.
How can you share Application State in a web farm or a web garden?
To share data across multiple sessions in a Web garden or Web farm, you must save and restore the information using a resource that is available to all the processes. This can be done through an XML file, a database, or some other resource using the standard file or database access methods.
What are the two built-in ways provided by ASP.NET to share Session state information across a Web garden or Web farm?
ASP.NET provides two built-in ways to share Session state information across a Web garden or Web farm. You can share Session state using:
A state server, as specified by a network location
This technique is simple to implement and doesn’t require you to install Microsoft SQL Server.
A SQL database, as specified by a SQL connection
This technique provides the best performance for storing and retrieving state information.
What are the steps to follow to share Session state information using a state server?
To share Session state information using a state server, follow these steps:
1. In the Web application’s Web.config file, set the sessionState element’s mode and stateConnectionString attributes.
2. Run the aspnet_state.exe utility on the Session state server. The aspnet_state.exe utility is installed in the \WINDOWS\Microsoft.NET \Framework\version folder when you install Visual Studio .NET Professional or Visual Studio .NET Enterprise Architect editions.
What are the steps to follow to share Session state information using a SQL database?
To share Session state information using a SQL database, follow these steps:
1. In the Web application’s Web.config file, set the sessionState element’s mode and sqlConnectionString attributes.
2. Run the InstallSqlState.sql utility on the Session state server. This utility installs the SQL database that shares Session state information across processes. The InstallSqlState.sql utility is installed in the \WINDOWS\Microsoft.NET \Framework\version folder when you install Visual Studio .NET Professional, Visual Studio .NET Enterprise Developer, or Visual Studio .NET Enterprise Architect editions.
Web application maintainance related ASP.NET Interview Questions
Why is it important to monitor a deployed a Web application?
After you have deployed a Web application, you need to monitor how it performs on the server. Many issues can crop up at this point because of
1. The number of users accessing the application.
2. The unpredictable nature of user interaction.
3. The possibility of malicious attack.
What are the 3 major steps invloved in maintaining a deployed web application?
Maintaining a deployed application is an ongoing task that involves three major steps:
1. Monitoring the application for error, performance, and security issues.
2. Repairing the application as issues are discovered.
3. Tuning the application to respond to user traffic.
What are the MMC snap-ins provided by windows for monitoring security, performance, and error events?
The Event Viewer snap-in : Lists application, system, and security events as they occur on the system. Use this tool to see what is currently happening on the server and to get specific information about a particular event.
The Performance snap-in : Lets you create new events to display in the Event Viewer and allows you to track event counters over time for display graphically or in report form.
How do you run the Event Viewer to view application, system, and security events as they happen?
To run the Event Viewer, choose Event Viewer from the Administrative Tools submenu on the Windows Start menu. (You can show the Administrative Tools menu in Windows XP Professional by opening the Start button’s Properties dialog box and clicking the Customize button on the Start Menu tab. The Administrative Tools option is located on the Advanced tab of the Customize Start Menu dialog box.) After clicking the Event Viewer shortcut, Windows displays the Event Viewer snap-in in the MMC.
What are the 3 levels at which the Event Viewer snap-in displays general application, system, and security events?
1. Informational events.
2. Warning events.
3. Error events.
Can you repair a deployed web application in place without restarting the server or IIS?
Yes, to repair a deployed Web application, copy the new assembly (.dll) and/or content files (.aspx, .ascx, and so on) to the application folder on the server. ASP.NET automatically restarts the application when you replace the assembly. You do not need to install or register the assembly on the server.
What is ASP.NET Process recycling?
ASP.NET Web applications have a limited ability to repair themselves through process recycling. Process recycling is the technique of shutting down and restarting an ASP.NET worker process (aspnet_wp.exe) that has become inactive or is consuming excessive resources. You can control how ASP.NET processes are recycled through attributes in the processModel element in the Machine.config file.
Describes the processModel attributes found in machine.config that relate to process recycling?
1. timeout attribute :The amount of time (hh:mm:ss) before the process is shut down and restarted. Use this setting to automatically recycle a process after a certain number of requests as a preventive measure.
2. shutDownTimeOut attribute : How much time each process has to shut itself down. After this amount of time, the process is terminated by the system if it still running.
3. requestLimit attribute : The number of queued requests to serve before the process is shut down and restarted. Use this setting the same way you use the timeout attribute.
4. restartQueueLimit attribute : The number of queued requests to retain while the process is shut down and restarted.
5. memoryLimit attribute : The percentage of physical memory the ASP.NET process is allowed to consume before that process is shut down and a new process is started. This setting helps prevent memory leaks from degrading the server.
6. responseRestart - DeadlockInterval : The amount of time to wait before restarting a process that was shut down because it was deadlocked. This setting is usually several minutes to prevent applications with serious errors from degrading the server.
7. responseDeadlockInterval : The amount of time to wait before restarting a process that is deadlocked. The process is restarted if there are queued requests and the process has not responded within this time limit.
What is the use of processModel element apart from providing process recycling?
The processModel element in the server’s Machine.config file provides attributes that control certain performance aspects, such as
1. The maximum number of requests to be queued.
2. How long to wait before checking whether a client is connected.
3. How many threads to allow per processor.
Describe the processModel attributes that relate to performance tuning?
requestQueueLimit
The number of queued requests allowed before ASP.NET returns response code 503 (Server too busy) to new requests
clientConnectedCheck
The amount of time (hh:mm:ss) to wait before checking whether a client is still connected
maxWorkerThreads
The maximum number of threads per processor
maxIOThreads
The maximum number of I/O threads per processor
In general, lowering these settings allows your server to handle fewer clients more quickly. Increasing these settings permits more clients and more queued requests, but slows response times.
How do you turn off Session state?
To turn off Session state, in the application’s Web.config file, set the sessionState element’s mode attribute to Off.
If you turn of Session State, can you use Session state variables in code anywhere in the application?
No
What is Optimization?
Optimization usually refers to writing code in a way that executes more quickly or consumes fewer resources. In general, optimizations simply reflect the good programming practices.
List some of the common steps to follow to optimize a web application for performance?
Turn off debugging for deployed applications.
Code that has been compiled with release options runs faster than code compiled with debug options.
Avoid round-trips between the client and server.
ASP.NET uses postbacks to process server events on a page. Try to design Web forms so that the data on the Web form is complete before the user posts the data to the server. You can use the validation controls to ensure that data is complete on the client side before the page is submitted.
Turn off Session state if it isn’t needed.
In some cases, you can design your code to use other techniques, such as cookies, to store client data.
Turn off ViewState for server controls that do not need to retain their values.
Saving ViewState information adds to the amount of data that must be transmitted back to the server with each request.
Use stored procedures with databases.
Stored procedures execute more quickly than ad hoc queries.
Use SqlDataReader rather than data sets for read-forward data retrieval.
Using SqlDataReader is faster and consumes less memory than creating a data set.
ASP.NET ViewState related Interview Questions
What is ViewState?
Web forms have very short lifetimes.In ASP.NET, the data that is entered in controls is encoded and stored in a hidden field. This encoded data is then sent with each request and restored to controls in Page_Init. The data in these controls is then available in the Page_Load event.The data that ASP.NET preserves between requests is called the Web form’s view state.
How do you enable or disable a ViewState for a control on the page?
Every ASP.NET control has a property called EnableViewState. If EnableViewState is set to true ViewState is enabled for the control. If EnableViewState is set to false ViewState is disabled for the control.
How do you enable or disable a ViewState at the page level?
At the page level you can enable or disable ViewState using EnableViewState property of the page.
What is the name of the hidden form field in which ViewState of the page is saved?
__ViewState
What are the performance implications of ViewState?
ViewState is usually good to retain the state of the controls on the webform across postbacks. If you have a huge DataGrid with tons of data being loaded on every page load. It is a good idea to disable the ViewState of the DataGrid for the page to load faster. If the ViewState of a large DataGrid is not disabled, ViewState can easily get very large, on the order of tens of kilobytes. Not only does the __ViewState form field cause slower downloads, but, whenever the user posts back the Web page, the contents of this hidden form field must be posted back in the HTTP request, thereby lengthening the request time, as well.
When does ViewState restoration happens?
During the Page_Init event
What are the disadvantages of using ViewState?
1. On all page visits, during the save view state stage the Page class gathers the collective view state for all of the controls in its control hierarchy and serializes the state to a base-64 encoded string. (This is the string that is emitted in the hidden __ViewState form filed.) Similarly, on postbacks, the load view state stage needs to deserialize the persisted view state data, and update the pertinent controls in the control hierarchy.
2. The __ViewState hidden form field adds extra size to the Web page that the client must download. For some view state-heavy pages, this can be tens of kilobytes of data, which can require several extra seconds (or minutes!) for modem users to download. Also, when posting back, the __ViewState form field must be sent back to the Web server in the HTTP POST headers, thereby increasing the postback request time.
Is ViewState encoded?
Yes, ViewState is base-64 encoded.Can you encrypt ViewState of Page?Yes, we can use the LosFormatter class to encrypt ViewState of Page
Can the HTML controls retian State accross postbacks?
No, by default HTML controls donot retain state accross postbacks.
Can you make HTML controls retain State accross postbacks?
Yes, HTML controls can retain State accross postbacks, if you convert HTML controls to Server Controls. There are 2 ways to convert HTML control to Server Controls.
1. Right click on the HTML Control and then click "Run As Server Control"
Or
2. Set runat="server" attribute for the Control.
Is ViewState supported in classic ASP?
No,ViewState is introduced in asp.net, it was not in classic asp.
When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a form with a lot of information and the server comes back with an error. You will have to go back to the form and correct the information. You click the back button, and what happens.......ALL form values are CLEARED, and you will have to start all over again! The site did not maintain your ViewState.
When a form is submitted in ASP .NET, the form reappears in the browser window together with all form values. How come? This is because ASP .NET maintains your ViewState. The ViewState indicates the status of the page when submitted to the server.Is ViewState of one page available to another page?No, ViewState of a Page is available only in that page. You cannot access ViewState of one page from another page.
Can you programatically store and retrieve data from ViewState?
Yes. In ASP.NET you can programatically store and retrieve data from ViewState.See the example below
//Save the value in ViewState objectViewState("SomeVar") = txtFirstName.text;
//Retrieve the value from ViewState objectString strFirstName = ViewState("SomeVar").ToString();
Can someone view the Page HTML source and read ViewState?
No. ViewState is base-64 encoded. Hence you cannot read ViewState. If you right click on the Page and View Source you will find __ViewState is base-64 encoded.
What happens during the Page_Init event?
The server controls are loaded and initialized from the Web form’s view state. This is the first step in a Web form’s life cycle.
Web forms have very short lifetimes.In ASP.NET, the data that is entered in controls is encoded and stored in a hidden field. This encoded data is then sent with each request and restored to controls in Page_Init. The data in these controls is then available in the Page_Load event.The data that ASP.NET preserves between requests is called the Web form’s view state.
How do you enable or disable a ViewState for a control on the page?
How do you enable or disable a ViewState at the page level?
At the page level you can enable or disable ViewState using EnableViewState property of the page.
What is the name of the hidden form field in which ViewState of the page is saved?
__ViewState
What are the performance implications of ViewState?
ViewState is usually good to retain the state of the controls on the webform across postbacks. If you have a huge DataGrid with tons of data being loaded on every page load. It is a good idea to disable the ViewState of the DataGrid for the page to load faster. If the ViewState of a large DataGrid is not disabled, ViewState can easily get very large, on the order of tens of kilobytes. Not only does the __ViewState form field cause slower downloads, but, whenever the user posts back the Web page, the contents of this hidden form field must be posted back in the HTTP request, thereby lengthening the request time, as well.
When does ViewState restoration happens?
During the Page_Init event
What are the disadvantages of using ViewState?
1. On all page visits, during the save view state stage the Page class gathers the collective view state for all of the controls in its control hierarchy and serializes the state to a base-64 encoded string. (This is the string that is emitted in the hidden __ViewState form filed.) Similarly, on postbacks, the load view state stage needs to deserialize the persisted view state data, and update the pertinent controls in the control hierarchy.
2. The __ViewState hidden form field adds extra size to the Web page that the client must download. For some view state-heavy pages, this can be tens of kilobytes of data, which can require several extra seconds (or minutes!) for modem users to download. Also, when posting back, the __ViewState form field must be sent back to the Web server in the HTTP POST headers, thereby increasing the postback request time.
Is ViewState encoded?
Yes, ViewState is base-64 encoded.Can you encrypt ViewState of Page?Yes, we can use the LosFormatter class to encrypt ViewState of Page
Can the HTML controls retian State accross postbacks?
Can you make HTML controls retain State accross postbacks?
Yes, HTML controls can retain State accross postbacks, if you convert HTML controls to Server Controls. There are 2 ways to convert HTML control to Server Controls.
1. Right click on the HTML Control and then click "Run As Server Control"
Or
2. Set runat="server" attribute for the Control.
Is ViewState supported in classic ASP?
No,ViewState is introduced in asp.net, it was not in classic asp.
When a form is submitted in classic ASP, all form values are cleared. Suppose you have submitted a form with a lot of information and the server comes back with an error. You will have to go back to the form and correct the information. You click the back button, and what happens.......ALL form values are CLEARED, and you will have to start all over again! The site did not maintain your ViewState.
When a form is submitted in ASP .NET, the form reappears in the browser window together with all form values. How come? This is because ASP .NET maintains your ViewState. The ViewState indicates the status of the page when submitted to the server.Is ViewState of one page available to another page?No, ViewState of a Page is available only in that page. You cannot access ViewState of one page from another page.
Can you programatically store and retrieve data from ViewState?
Yes. In ASP.NET you can programatically store and retrieve data from ViewState.See the example below
//Save the value in ViewState objectViewState("SomeVar") = txtFirstName.text;
//Retrieve the value from ViewState objectString strFirstName = ViewState("SomeVar").ToString();
Can someone view the Page HTML source and read ViewState?
No. ViewState is base-64 encoded. Hence you cannot read ViewState. If you right click on the Page and View Source you will find __ViewState is base-64 encoded.
What happens during the Page_Init event?
The server controls are loaded and initialized from the Web form’s view state. This is the first step in a Web form’s life cycle.
Interview Questions on ASP.NET Validation controls
What are ASP.NET Validation controls?
ASP.NET provides validation controls to help you check Web form data entries before the data is accepted and saved in the Database. Validation controls can be used to address the following questions.
1. Did the user enter anything?
2. Is the entry the appropriate kind of data (For example, Date of Birth should be a valid Date, Name should be a string etc.)?
3. Is the data within a required range?(For example age cannot be greater than 100 years)
The validation controls check the validity of data entered in associated server controls on the client before the page is posted back to the server.Most validity problems can be caught and corrected by the user without a round-trip to the server.
Where do the ASP.NET validation controls validate data, on the Client or on the Web Server?
ASP.NET validation controls validate data first on the client and then on the web server. If a client disables javascript on the browser then, client side validations are bypassed and validations are performed on the web server.
Client-side validation is provided by a JScript library named WebUIValidation.js, which is downloaded separately to the client. Validation controls also automatically provide server-side validation. Server-side validation is always performed, whether or not client-side validation has occurred. This double-checking ensures that custom validations are performed correctly and that client-side validation has not been circumvented.
What are the 6 different validation controls provided by ASP.NET?
RequiredFieldValidator:Checks whether a control contains data
CompareValidator:Checks whether an entered item matches an entry in another control
RangeValidator:Checks whether an entered item is between two values
RegularExpressionValidator:Checks whether an entered item matches a specified format
CustomValidator:Checks the validity of an entered item using a client-side script or a server-side code, or both
ValidationSummary:Displays validation errors in a central location or display a general validation error description
What property of the validation control is used to specify which control to validate?ControlToValidate property.
Explain in simple steps how to use validation controls?
1.Draw a validation control on a Web form and set its ControlToValidate property to the control you want to validate.
2.If you’re using the CompareValidator control, you also need to specify the ControlToCompare property.
3.Set the validation control’s ErrorMessage property to the error message you want displayed if the control’s data is not valid.
4.Set the validation control’s Text property if you want the validation control to display a message other than the message in the ErrorMessage property when an error occurs. Setting the Text property lets you briefly indicate where the error occurred on the form and display the longer ErrorMessage property in a ValidationSummary control.
5.Draw a ValidationSummary control on the Web form to display the error messages from the validation controls in one place.
6.Provide a control that triggers a postback event. Although validation occurs on the client side, validation doesn’t start until a postback is requested.
Are the validation controls fired on the client side if javascript is disabled on the client browser?
No, validation controls are not fired on the client side if javascript is disabled on the client browser.
What is the use of CausesValidation property of an ASP.NET button control?
CausesValidation property of an ASP.NET button control is used to determine if the validation controls should be fired when the button is clicked. If CausesValidation property is set to true, then validation is performed and if the CausesValidation property is set to false then validation is not done.
Give an example of real time scenario where you might use CausesValidation property of an ASP.NET button control?
Let us assume we have a Page that collects user information like name, age, date of birth, gender with a submit and reset buttons. When I click the submit button the information filled on the form should be validated and saved to the database. If I click the reset button then all the controls on the webform should default to their initial values without validation happening.So you have to set the CausesValidation property of the reset button to false for the validation to be bypassed. Other wise you will not be able to post back the page to the server.
What is ASP.NET Custom Validator used for?
ASP.NET Custom Validator is used to perform complex types of validation not provided by the standard validation control, use a CustomValidator control and write code to perform the validation on the server side and optionally on the client side.
How do you programatically check, if the client side validation is not bypassed by disabling the javascript on the client browser?
We use Page.IsValid property to determine if all the validations have succeeded. For this property to return true, all validation server controls in the current validation group must validate successfully.
How do you programatically invoke all validation controls on a page?
Call Page.Validate() method. When this method is invoked, it iterates through the validation controls contained in the ValidatorCollection object associated with the Page.Validators property and invokes the validation logic for each validation control in the current validation group.
What is a validation group?
Validation groups allow you to group validation controls on a page as a set. Each validation group can perform validation independently from other validation groups on the page.
How do you create a validation group?
You create a validation group by setting the ValidationGroup property to the same name for all the controls you want to group. You can assign any name to a validation group, but you must use the same name for all members of the group.
Explain how a validation group works when the Page is posted by clicking a button?
During postback, the Page class's IsValid property is set based only on the validation controls in the current validation group. The current validation group is determined by the control that caused validation to occur. For example, if a button control with a validation group of LoginGroup is clicked, then the IsValid property will return true if all validation controls whose ValidationGroup property is set to LoginGroup are valid.
Can a DropDownList fire validation controls?
Yes, DropDownList control can also fire validation if the control's CausesValidation property is set to true and the AutoPostBack property is set to true.
How do you programatically force all validation controls in a particular validation group to be fired?
Call the Page.Validate(string GroupName) method and pass the name of the validation group. This will fire only the validation controls in that validation group.
What is SetFocusOnError property of a validation control used for?
Use the SetFocusOnError property to specify whether focus is automatically set to the control specified by the ControlToValidate property when this validation control fails. This allows the user to quickly update the appropriate control.
If multiple validation controls fail and this property is set to true, the control specified in the ControlToValidate property for the first validation control receives focus.
What is InitialValue property of a RequiredFieldValidator?
Use this property to specify the initial value of the input control.Validation fails only if the value of the associated input control matches this InitialValue upon losing focus.
1. Did the user enter anything?
2. Is the entry the appropriate kind of data (For example, Date of Birth should be a valid Date, Name should be a string etc.)?
3. Is the data within a required range?(For example age cannot be greater than 100 years)
The validation controls check the validity of data entered in associated server controls on the client before the page is posted back to the server.Most validity problems can be caught and corrected by the user without a round-trip to the server.
Where do the ASP.NET validation controls validate data, on the Client or on the Web Server?
ASP.NET validation controls validate data first on the client and then on the web server. If a client disables javascript on the browser then, client side validations are bypassed and validations are performed on the web server.
Client-side validation is provided by a JScript library named WebUIValidation.js, which is downloaded separately to the client. Validation controls also automatically provide server-side validation. Server-side validation is always performed, whether or not client-side validation has occurred. This double-checking ensures that custom validations are performed correctly and that client-side validation has not been circumvented.
What are the 6 different validation controls provided by ASP.NET?
RequiredFieldValidator:Checks whether a control contains data
CompareValidator:Checks whether an entered item matches an entry in another control
RangeValidator:Checks whether an entered item is between two values
RegularExpressionValidator:Checks whether an entered item matches a specified format
CustomValidator:Checks the validity of an entered item using a client-side script or a server-side code, or both
ValidationSummary:Displays validation errors in a central location or display a general validation error description
What property of the validation control is used to specify which control to validate?ControlToValidate property.
Explain in simple steps how to use validation controls?
1.Draw a validation control on a Web form and set its ControlToValidate property to the control you want to validate.
2.If you’re using the CompareValidator control, you also need to specify the ControlToCompare property.
3.Set the validation control’s ErrorMessage property to the error message you want displayed if the control’s data is not valid.
4.Set the validation control’s Text property if you want the validation control to display a message other than the message in the ErrorMessage property when an error occurs. Setting the Text property lets you briefly indicate where the error occurred on the form and display the longer ErrorMessage property in a ValidationSummary control.
5.Draw a ValidationSummary control on the Web form to display the error messages from the validation controls in one place.
6.Provide a control that triggers a postback event. Although validation occurs on the client side, validation doesn’t start until a postback is requested.
Are the validation controls fired on the client side if javascript is disabled on the client browser?
No, validation controls are not fired on the client side if javascript is disabled on the client browser.
What is the use of CausesValidation property of an ASP.NET button control?
CausesValidation property of an ASP.NET button control is used to determine if the validation controls should be fired when the button is clicked. If CausesValidation property is set to true, then validation is performed and if the CausesValidation property is set to false then validation is not done.
Give an example of real time scenario where you might use CausesValidation property of an ASP.NET button control?
What is ASP.NET Custom Validator used for?
ASP.NET Custom Validator is used to perform complex types of validation not provided by the standard validation control, use a CustomValidator control and write code to perform the validation on the server side and optionally on the client side.
How do you programatically check, if the client side validation is not bypassed by disabling the javascript on the client browser?
We use Page.IsValid property to determine if all the validations have succeeded. For this property to return true, all validation server controls in the current validation group must validate successfully.
How do you programatically invoke all validation controls on a page?
Call Page.Validate() method. When this method is invoked, it iterates through the validation controls contained in the ValidatorCollection object associated with the Page.Validators property and invokes the validation logic for each validation control in the current validation group.
What is a validation group?
Validation groups allow you to group validation controls on a page as a set. Each validation group can perform validation independently from other validation groups on the page.
How do you create a validation group?
You create a validation group by setting the ValidationGroup property to the same name for all the controls you want to group. You can assign any name to a validation group, but you must use the same name for all members of the group.
Explain how a validation group works when the Page is posted by clicking a button?
During postback, the Page class's IsValid property is set based only on the validation controls in the current validation group. The current validation group is determined by the control that caused validation to occur. For example, if a button control with a validation group of LoginGroup is clicked, then the IsValid property will return true if all validation controls whose ValidationGroup property is set to LoginGroup are valid.
Can a DropDownList fire validation controls?
Yes, DropDownList control can also fire validation if the control's CausesValidation property is set to true and the AutoPostBack property is set to true.
How do you programatically force all validation controls in a particular validation group to be fired?
Call the Page.Validate(string GroupName) method and pass the name of the validation group. This will fire only the validation controls in that validation group.
What is SetFocusOnError property of a validation control used for?
Use the SetFocusOnError property to specify whether focus is automatically set to the control specified by the ControlToValidate property when this validation control fails. This allows the user to quickly update the appropriate control.
If multiple validation controls fail and this property is set to true, the control specified in the ControlToValidate property for the first validation control receives focus.
What is InitialValue property of a RequiredFieldValidator?
Use this property to specify the initial value of the input control.Validation fails only if the value of the associated input control matches this InitialValue upon losing focus.
Transactions related ASP.NET Interview Questions
What is a transaction?
A transaction is a group of commands that change the data stored in a database. The transaction, which is treated as a single unit, assures that the commands are handled in an all-or-nothing fashion. if one of the commands fails, all of the commands fail, and any data that was written to the database by the commands is backed out. In this way, transactions maintain the integrity of data in a database. ADO.NET lets you group database operations into transactions.
What is the main purpose of database transactions?
The main purpose of database transactions is to maintain the integrity of data in a database.
How do you determine which SQL commands are part of a transaction?
You can determine what database commands belong in a transaction by using the ACID test. Commands must be atomic, consistent, isolated, and durable.
Commands belong in a transaction if they are:
Atomic:In other words, they make up a single unit of work. For example, if a customer moves, you want your data entry operator to change all of the customer’s address fields as a single unit, rather than changing street, then city, then state, and so on.
Consistent:All the relationships between data in a database are maintained correctly. For example, if customer information uses a tax rate from a state tax table, the state entered for the customer must exist in the state tax table.
Isolated:Changes made by other clients can’t affect the current changes. For example, if two data entry operators try to make a change to the same customer at the same time, one of two things occurs: either one operator’s changes are accepted and the other is notified that the changes weren’t made, or both operators are notified that their changes were not made. In either case, the customer data is not left in an indeterminate state.
Durable:Once a change is made, it is permanent. If a system error or power failure occurs before a set of commands is complete, those commands are undone and the data is restored to its original state once the system begins running again.
Why is transaction processing very important for web applications?
Transaction processing is very important for Web applications that use data access, because Web applications are distributed among many different clients. In a Web application, databases are a shared resource, and having many different clients distributed over a wide area can present the below key problems.
Contention for resources:Several clients might try to change the same record at the same time. This problem gets worse the more clients you have.
Unexpected failures:The Internet is not the most reliable network around, even if your Web application and Web server are 100 percent reliable. Clients can be unexpectedly disconnected by their service providers, by their modems, or by power failures.
Web application life cycle:Web applications don’t follow the same life cycle as Windows applications—Web forms live for only an instant, and a client can leave your application at any point by simply typing a new address in his or her browser.
List the steps in order to process a transaction?
1.Begin a transaction.
2.Process database commands.
3.Check for errors.
4.If errors occurred, restore the database to its state at the beginning of the transaction. If no errors occurred, commit the transaction to the database.
Explain how a DataSet provides transaction processing?
DataSet provide transaction processing through the RejectChanges and Update methods. DataSet also provide an AcceptChanges method that resets the state of records in a data set to Unchanged. Data sets provide implicit transaction processing, because changes to a data set are not made in the database until you invoke the Update method on the data adapter object. This lets you perform a set of commands on the data and then choose a point at which to make the changes permanent in the database.
If an error occurs during the Update method, none of the changes from the data set is made in the database. At that point, you can either attempt to correct the error and try the Update method again or undo the changes pending in the data set using the data set’s RejectChanges method.
Give an example to show how DataSets provide transaction processing?
Let us assume we have a DataGrid that displays employee information. Every row also has a delete button, which when you click will delete that row. On this page we also have a Restore and Commit buttons. When you click the Restore button you should be able to restore the data to its previous state. When you click the Commit button you should be able to update the database with the deletions made in the DataSet.
The code for Commit and Restore buttons is shown below.private void butRestore_Click(object sender, System.EventArgs e)
{
// Restore the data set to its original state.
dsContacts.RejectChanges();
// Refresh the data grid.
grdContacts.DataBind();
}
private void butCommit_Click(object sender, System.EventArgs e)
{
int intRows;
// Update the database from the data set.
intRows = adptContacts.Update(dsContacts);
// Save changes to state variable.
Session["dsContacts"] = dsContacts;
// Refresh the data grid.
grdContacts.DataBind();
}The RejectChanges method in the preceding butRestore_Click event procedure returns the data set to its state before the row was deleted. The data set’s AcceptChanges method is the inverse of RejectChanges—it resets the DataRowState property for all the changed rows in a data set to Unchanged and removes any deleted rows.
The AcceptChanges method prevents the Update method from making those changes in the database, however, because Update uses the rows’ DataRowState property to determine which rows to modify in the database. For this reason, the AcceptChanges method is useful only when you do not intend to update a database from the data set.
What are the 3 types of transaction objects available in ADO.NET?
As we have 3 types of database connections in ADO.NET, there are also 3 types of transaction objects:
SqlTransaction
OracleTransaction
OleDbTransaction
What are the steps involved in using a transaction object in ADO.NET?
1.Open a database connection.
2.Create the transaction object using the database connection object’s BeginTransaction method.
3.Create command objects to track with this transaction, assigning the Transaction property of each command object to the name of the transaction object created in step 2.
4.Execute the commands. Because the purpose of transaction processing is to detect and correct errors before data is written to the database, this is usually done as part of an error-handling structure.
5.Commit the changes to the database or restore the database state, depending on the success of the commands.
Close the database connection.
What property of a transaction object determines how concurrent changes to a database are handled?
IsolationLevel property of the transaction object is used to determine how concurrent changes to a database are handled.
What are different isolation levels of a transaction object in ADO.NET?
ReadUncommitted:Does not lock the records being read. This means that an uncommitted change can be read and then rolled back by another client, resulting in a local copy of a record that is not consistent with what is stored in the database. This is called a dirty read because the data is inconsistent.
Chaos:Behaves the same way as ReadUncommitted, but checks the isolation level of other pending transactions during a write operation so that transactions with more restrictive isolation levels are not overwritten.
ReadCommitted:Locks the records being read and immediately frees the lock as soon as the records have been read. This prevents any changes from being read before they are committed, but it does not prevent records from being added, deleted, or changed by other clients during the transaction. This is the default isolation level.
RepeatableRead:Locks the records being read and keeps the lock until the transaction completes. This ensures that the data being read does not change during the transaction.
Serializable:Locks the entire data set being read and keeps the lock until the transaction completes. This ensures that the data and its order within the database do not change during the transaction.
What is the default isolation level in a transaction?
ReadCommitted
What is a Save Point in a transaction in ADO.NET?
SqlConnection object provide one transaction capability that is unavailable for OLE database connections: the ability to create save points within a transaction. Save points let you restore the database state to a specific position within the current transaction. To set a save point within a SQL transaction, use the Save method as shown below.TransactionObject.Save("FirstStep");
How do you restore a SQL transaction to a specific save point?
To restore a SQL transaction to a save point, specify the name of the save point in the Rollback method as shown below.
TransactionObject.Rollback("FirstStep");
A transaction is a group of commands that change the data stored in a database. The transaction, which is treated as a single unit, assures that the commands are handled in an all-or-nothing fashion. if one of the commands fails, all of the commands fail, and any data that was written to the database by the commands is backed out. In this way, transactions maintain the integrity of data in a database. ADO.NET lets you group database operations into transactions.
What is the main purpose of database transactions?
The main purpose of database transactions is to maintain the integrity of data in a database.
How do you determine which SQL commands are part of a transaction?
Commands belong in a transaction if they are:
Atomic:In other words, they make up a single unit of work. For example, if a customer moves, you want your data entry operator to change all of the customer’s address fields as a single unit, rather than changing street, then city, then state, and so on.
Consistent:All the relationships between data in a database are maintained correctly. For example, if customer information uses a tax rate from a state tax table, the state entered for the customer must exist in the state tax table.
Isolated:Changes made by other clients can’t affect the current changes. For example, if two data entry operators try to make a change to the same customer at the same time, one of two things occurs: either one operator’s changes are accepted and the other is notified that the changes weren’t made, or both operators are notified that their changes were not made. In either case, the customer data is not left in an indeterminate state.
Durable:Once a change is made, it is permanent. If a system error or power failure occurs before a set of commands is complete, those commands are undone and the data is restored to its original state once the system begins running again.
Why is transaction processing very important for web applications?
Transaction processing is very important for Web applications that use data access, because Web applications are distributed among many different clients. In a Web application, databases are a shared resource, and having many different clients distributed over a wide area can present the below key problems.
Contention for resources:Several clients might try to change the same record at the same time. This problem gets worse the more clients you have.
Unexpected failures:The Internet is not the most reliable network around, even if your Web application and Web server are 100 percent reliable. Clients can be unexpectedly disconnected by their service providers, by their modems, or by power failures.
Web application life cycle:Web applications don’t follow the same life cycle as Windows applications—Web forms live for only an instant, and a client can leave your application at any point by simply typing a new address in his or her browser.
List the steps in order to process a transaction?
1.Begin a transaction.
2.Process database commands.
3.Check for errors.
4.If errors occurred, restore the database to its state at the beginning of the transaction. If no errors occurred, commit the transaction to the database.
Explain how a DataSet provides transaction processing?
DataSet provide transaction processing through the RejectChanges and Update methods. DataSet also provide an AcceptChanges method that resets the state of records in a data set to Unchanged. Data sets provide implicit transaction processing, because changes to a data set are not made in the database until you invoke the Update method on the data adapter object. This lets you perform a set of commands on the data and then choose a point at which to make the changes permanent in the database.
If an error occurs during the Update method, none of the changes from the data set is made in the database. At that point, you can either attempt to correct the error and try the Update method again or undo the changes pending in the data set using the data set’s RejectChanges method.
Give an example to show how DataSets provide transaction processing?
Let us assume we have a DataGrid that displays employee information. Every row also has a delete button, which when you click will delete that row. On this page we also have a Restore and Commit buttons. When you click the Restore button you should be able to restore the data to its previous state. When you click the Commit button you should be able to update the database with the deletions made in the DataSet.
The code for Commit and Restore buttons is shown below.private void butRestore_Click(object sender, System.EventArgs e)
{
// Restore the data set to its original state.
dsContacts.RejectChanges();
// Refresh the data grid.
grdContacts.DataBind();
}
private void butCommit_Click(object sender, System.EventArgs e)
{
int intRows;
// Update the database from the data set.
intRows = adptContacts.Update(dsContacts);
// Save changes to state variable.
Session["dsContacts"] = dsContacts;
// Refresh the data grid.
grdContacts.DataBind();
}The RejectChanges method in the preceding butRestore_Click event procedure returns the data set to its state before the row was deleted. The data set’s AcceptChanges method is the inverse of RejectChanges—it resets the DataRowState property for all the changed rows in a data set to Unchanged and removes any deleted rows.
The AcceptChanges method prevents the Update method from making those changes in the database, however, because Update uses the rows’ DataRowState property to determine which rows to modify in the database. For this reason, the AcceptChanges method is useful only when you do not intend to update a database from the data set.
What are the 3 types of transaction objects available in ADO.NET?
SqlTransaction
OracleTransaction
OleDbTransaction
What are the steps involved in using a transaction object in ADO.NET?
1.Open a database connection.
2.Create the transaction object using the database connection object’s BeginTransaction method.
3.Create command objects to track with this transaction, assigning the Transaction property of each command object to the name of the transaction object created in step 2.
4.Execute the commands. Because the purpose of transaction processing is to detect and correct errors before data is written to the database, this is usually done as part of an error-handling structure.
5.Commit the changes to the database or restore the database state, depending on the success of the commands.
Close the database connection.
What property of a transaction object determines how concurrent changes to a database are handled?
IsolationLevel property of the transaction object is used to determine how concurrent changes to a database are handled.
What are different isolation levels of a transaction object in ADO.NET?
ReadUncommitted:Does not lock the records being read. This means that an uncommitted change can be read and then rolled back by another client, resulting in a local copy of a record that is not consistent with what is stored in the database. This is called a dirty read because the data is inconsistent.
Chaos:Behaves the same way as ReadUncommitted, but checks the isolation level of other pending transactions during a write operation so that transactions with more restrictive isolation levels are not overwritten.
ReadCommitted:Locks the records being read and immediately frees the lock as soon as the records have been read. This prevents any changes from being read before they are committed, but it does not prevent records from being added, deleted, or changed by other clients during the transaction. This is the default isolation level.
RepeatableRead:Locks the records being read and keeps the lock until the transaction completes. This ensures that the data being read does not change during the transaction.
Serializable:Locks the entire data set being read and keeps the lock until the transaction completes. This ensures that the data and its order within the database do not change during the transaction.
What is the default isolation level in a transaction?
ReadCommitted
What is a Save Point in a transaction in ADO.NET?
SqlConnection object provide one transaction capability that is unavailable for OLE database connections: the ability to create save points within a transaction. Save points let you restore the database state to a specific position within the current transaction. To set a save point within a SQL transaction, use the Save method as shown below.TransactionObject.Save("FirstStep");
How do you restore a SQL transaction to a specific save point?
To restore a SQL transaction to a save point, specify the name of the save point in the Rollback method as shown below.
TransactionObject.Rollback("FirstStep");
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