ASP.Net Interview Questions - 1

  1. What is the sequence in which ASP.NET events are processed ?

    Following is the sequence in which the events occur (extremely simplified version, for more detailed description see another post):

    • Page_Init.
    • Page_Load.
    • Control events.
    • Page_Unload event.

    Page_Init event only occurs when first time the page is started, but Page_Load occurs in subsequent request of the page

  2. In which event are the controls fully loaded ?

    Page_Load event guarantees that all controls are fully loaded. Controls are also accessed in Page_Init events but you will see that viewstate is not fully loaded during this event

  3. How can we identify that the Page is PostBack?

    Page object has a "IsPostBack" property which can be checked to know that is the page posted back.

  4. How does ASP.NET maintain state in between subsequent request?

  5. What is event bubbling?

    Server controls like Datagrid, DataList, Repeater can have other child controls inside them. Example DataGrid can have combo box inside datagrid. These child controls do not raise there events by themselves, rather they pass the event to the container parent (which can be a DataGrid, DataList, Repeater), which passed to the page as "ItemCommand" event. As the child control send there events to parent this is termed as event bubbling.

  6. How do we assign page specific attributes?

    Page attributes are specified using the @Page directive.

  7. If we want to make sure that no one has tampered with ViewState, how do we ensure it?

    Set the @Page directive EnableViewStateMac to True.

  8. What is the use of @Register directives?

    @Register directive informs the compiler of any custom server control added to the page.

  9. What is SmartNavigation property?

    It’s a feature provided by ASP.NET to prevent flickering and redrawing when the page is posted back. It is supported by Internet Explorer only.

  10. What is AppSetting Section in "Web.Config" file ?

    Web.config file defines configuration for a webproject. Using "AppSetting" section we can define user defined values. For Example we can define "ConnectionString" section which will be used through out the project for database connection.


    <configuration>
    <appSettings>
    <add key="ConnectionString" value="server=xyz;pwd=www;database=testing" />
    </appSettings>

  11. Where is ViewState information stored?

    In HTML Hidden Fields.

  12. What is the use of @OutputCache directive in ASP.NET?

    It is basically used for caching.

  13. How can we create custom controls in ASP.NET ?

    User controls in ASP.NET are created using .ASCX files. After .ASCX file is created you need to two things in order that the ASCX can be used in project:

    • Register the ASCX control in page using the <%@ Register directive. Example <%@ Register tagprefix="Accounting" Tagname="footer" Src="Footer.ascx" %>
    • Now to use the above accounting footer in page you can use the below directive. <Accounting:footer runat="server" />

  14. What types of validation controls are provided by ASP.NET?

    There are six main types of validation controls:

    • RequiredFieldValidator - It checks whether the control have any value. It’s used when you want the control should not be empty.

    • RangeValidator - It checks if the value in validated control is in that specific range. Example txtCustomerCode should not be more than eight length.

    • CompareValidator - It checks that the value in controls should match some specific value. Example Textbox TxtPi should be equal to 3.14.

    • RegularExpressionValidator - When we want the control value should match with a specific regular expression.

    • CustomValidator - It is used to define user-defined validation.

    • ValidationSummary - It displays summary of all current validation errors.

  15. What is "AutoPostBack" feature in ASP.NET ?

    If we want the control to automatically postback in case of any event, we will need to check this attribute as true. Example on a ComboBox change we need to send the event immediately to the server side then set the "AutoPostBack " attribute to true.

  16. How can you enable automatic paging in DataGrid?

    In order to enable paging in Datagrid you need to (very short version):

    • Set the "AllowPaging" property to true.
    • In PageIndexChanged event handler set the current PageIndex clicked.
      Below is an example in C#:

      //Declaring DataGrid
      protected System.Web.UI.WebControls.DataGrid DataGrid1;
      //Binding DataGrid with a Data Source (DataSet in our Case)
      DataGrid1.DataSource = dataSet1;
      DataGrid1.DataBind();
      this.DataGrid1.PageIndexChanged += new System.Web.UI.WebControls.DataGridPageChangedEventHandler(this.GridPageIndexChanged);
      //Implement the EventHandler
      private void GridPageIndexChanged(object source, System.Web.UI.WebControls.DataGridPageChangedEventArgs e)
      {
      DataGrid1.CurrentPageIndex = e.NewPageIndex;
      //Bind the DataGrid again with the Data Source
      DataGrid1.DataSource = dataSet1;
      DataGrid1.DataBind();
      }

  17. What is the use of "GLOBAL.ASAX" file ?

    It allows to handle ASP.NET application level events and setting application-level variables.

  18. What is the difference between "Web.config" and "Machine.Config" ?

    "Web.config" files apply settings to each web application, while "Machine.config" file apply settings to all ASP.NET applications.

  19. What are SESSION and APPLICATION objects?

    In short, Session object stores information between HTTP requests for a particular user, while Application object is global across users.

  20. What is the difference between Server.Transfer and Response.Redirect ?

    Following are the major differences between them:

    • Response.Redirect sends message to the browser saying it to move to some different page, while Server.Transfer does not send any message to the browser but rather redirects the user directly from the server itself. So in Server.Transfer
      there is no round trip while Response.Redirect has a round trip and hence puts a load on server.
    • Using Server.Transfer you can not redirect to a different from the server itself. This cross server redirect is possible only using Response.Redirect.
    • With Server.Transfer you can preserve your information. It has a parameter called as "preserveForm". So the existing query string etc. will be able in the calling page.

  21. What is the difference between authentication and authorization?

    Authentication is verifying the identity of a user and authorization is process where we check does this identity have access rights to the system. In short we can say the following authentication is the process of obtaining some sort of credentials.from the users and using those credentials to verify the user’s identity. Authorization is the process of allowing an authenticated user access to resources. Authentication always proceed to Authorization; even if your application lets anonymous users connect and use the application, it still authenticates them as being anonymous.

  22. What is impersonation in ASP.NET?

    By default, ASP.NET executes in the security context of a restricted user account on the local machine. Sometimes you need to access network resources such as a file on a shared drive, which requires additional permissions. One way to overcome this restriction is to use impersonation. With impersonation, ASP.NET can execute the request using the identity of the client who is making the request, or ASP.NET can impersonate a specific account you specify in web.config.

  23. Explain in brief how the ASP.NET authentication process works.

    ASP.NET does not run by itself, it runs inside the process of IIS. So there are two authentication layers which exist in ASP.NET system. First authentication happens at the IIS level and then at the ASP.NET level depending on the WEB.CONFIG file :

    • IIS first checks to make sure the incoming request comes from an IP address that is allowed access to the domain. If not it denies the request.
    • Next IIS performs its own user authentication if it is configured to do so. By default IIS allows anonymous access, so requests are automatically authenticated, but you can change this default on a per – application basis with in IIS.
    • If the request is passed to ASP.Net with an authenticated user, ASP.Net checks to see whether impersonation is enabled. If impersonation is enabled, ASP.Net acts as though it were the authenticated user. If not ASP.Net acts with its own configured account.
    • Finally the identity from step 3 is used to request resources from the operating system. If ASP.net authentication can obtain all the necessary resources it grants the users request otherwise it is denied. Resources can include much more than just the ASP.net page itself you can also use .Net’s code access security features to extend this authorization step to disk files, registry keys and other resources.

  24. What are the various ways of authentication techniques in ASP.NET?

    Selecting an authentication provider is as simple as making an entry in the web.config file for the application. You can use one of these entries to select the corresponding built in authentication provider:

    • <authentication mode="windows">
    • <authentication mode="passport">
    • <authentication mode="forms">
    • Custom authentication where you might install an ISAPI filter in IIS that compares incoming requests to list of source IP addresses, and considers requests to be authenticated if they come from an acceptable address. In that case, you would set the authentication mode to none to prevent any of the .Net authentication providers from being triggered.

    Windows authentication and IIS

    If you select windows authentication for your ASP.NET application, you also have to configure authentication within IIS. This is because IIS provides Windows authentication. IIS gives you a choice for four different authentication methods: anonymous,basic,digest and windows integrated.

    If you select anonymous authentication, IIS doesn’t perform any authentication, Any one is allowed to access the ASP.NET application.

    If you select basic authentication, users must provide a windows username and password to connect. How ever this information is sent over the network in clear text, which makes basic authentication very much insecure over the internet.

    If you select digest authentication, users must still provide a windows user name and password to connect. However the password is hashed before it is sent across the network. Digest authentication requires that all users be running Internet Explorer 5 or later and that windows accounts to stored in active directory.

    If you select windows integrated authentication, passwords never cross the network.Users must still have a username and password, but the application uses either the Kerberos or challenge/response protocols authenticate the user. Windows-integrated authentication requires that all users be running Internet Explorer 3.01 or later Kerberos is a network
    authentication protocol. It is designed to provide strong authentication for client/server applications by using secret-key cryptography. Kerberos is a solution to network security problems. It provides the tools of authentication and strong cryptography over the network to help to secure information in systems across entire enterprise.

    Passport authentication

    Passport authentication lets you to use Microsoft’s passport service to authenticate users of your application. If your users have signed up with passport, and you configure the authentication mode of the application to the passport authentication, all authentication duties are off-loaded to the passport servers.

    Passport uses an encrypted cookie mechanism to indicate authenticated users. If users have already signed into passport when they visit your site, they’ll be considered authenticated by ASP.NET. Otherwise they’ll be redirected to the passport servers to log in. When they are successfully log in, they’ll be redirected back to your site

    To use passport authentication you have to download the Passport Software Development Kit (SDK) and install it on your server. The SDK can be found at Microsoft website. It includes full details of implementing passport authentication in your own applications.

    Forms authentication

    Forms authentication provides you with a way to handle authentication using your own custom logic with in an ASP.NET application. The following applies if you choose forms authentication.

    When a user requests a page for the application, ASP.NET checks for the presence of a special session cookie. If the cookie is present, ASP.NET assumes the user is authenticated and processes the request.

    If the cookie isn’t present, ASP.NET redirects the user to a web form you provide.

    You can carry out whatever authentication, it check’s you like it checks your form. When the user is authenticated, you indicate this to ASP.NET by setting a property, which creates the special cookie to handle subsequent requests.

  25. How does authorization work in ASP.NET?

    ASP.NET impersonation is controlled by entries in the applications web.config file. The default setting is "no impersonation". You can explicitly specify that ASP.NET shouldn’t use impersonation by including the following code in the file
    <identity impersonate="false"/>

    It means that ASP.NET will not perform any authentication and runs with its own privileges. By default ASP.NET runs as an unprivileged account named ASPNET. You can change this by making a setting in the processModel section of the machine.config file. When you make this setting, it automatically applies to every site on the server. To user a high-privileged system account instead of a low-privileged set the userName attribute of the processModel element to SYSTEM. Using this setting is a definite security risk, as it elevates the privileges of the ASP.NET process to a point where it can do bad things to
    the operating system.

    When you disable impersonation, all the request will run in the context of the account running ASP.NET: either the ASPNET account or the system account. This is true when you are using anonymous access or authenticating users in some fashion. After the user has been authenticated, ASP.NET uses its own identity to request access to resources.

    The second possible setting is to turn on impersonation. <identity impersonate="false"/>.

    In this case, ASP.NET takes on the identity IIS passes to it. If you are allowing anonymous access in IIS, this means ASP.NET will impersonate the IUSR_ComputerName account that IIS itself uses. If you aren’t allowing anonymous access, ASP.NET will take on the credentials of the authenticated user and make requests for resources as if it were that user. Thus by turning impersonation on and using a non-anonymous method of authentication in IIS, you can let users log on and use their identities within your ASP.NET application.

    Finally, you can specify a particular identity to use for all authenticated requests : <identity impersonate="false" username="DOMAIN\username" password="password"/>.

    With this setting, all the requests are made as the specified user (Assuming the password it correct in the configuration file). So, for example you could designate a user for a single application, and use that user’s identity every time someone authenticates to the application. The drawback to this technique is that you must embed the user’s password in the web.config file in plain text. Although ASP.NET won’t allow anyone to download this file, this is still a security risk if anyone can get the file by other means.

  26. What is the difference between Datagrid, Datalist and Repeater?

    A Datagrid, Datalist and Repeater are all ASP.NET data Web controls. They have many things in common like DataSource Property, DataBind Method, ItemDataBound and ItemCreated events.

    When you assign the DataSource Property of a DataGrid to a DataSet then each DataRow present in the DataRow Collection of DataTable is assigned to a corresponding DataGridItem and this is same for the rest of the two controls also. But The HTML code generated for a DataGrid has an HTML TABLE ROW (TR) element created for the particular DataRow and its a Table form representation with Columns and Rows.

    For a Datalist its an Array of Rows and based on the Template Selected and the RepeatColumn Property value We can specify how many DataSource records should appear per HTML <table> row. In short in DataGrid we have one record per row, but in DataList we can have five or six rows per row.

    For a Repeater Control, the DataRecords to be displayed depends upon the Templates specified and the only HTML generated is the due to the Templates.

    In addition to these, DataGrid has a in-built support for Sort, Filter and paging the data, which is not possible when using a DataList and for a Repeater Control we would require to write an explicit code to do paging.

  27. From performance point of view how do Datagrid, Datalist and Repeater rate ?

    Repeater is fastest, followed by DataList and finally DataGrid.

  28. What is the method to customize columns in DataGrid?

    Use the TemplateColumn.

  29. How can we format data inside DataGrid?

    Use the DataFormatString property.

  30. How to decide should you use a DataGrid, DataList or Repeater ?

    DataGrid provides ability to allow the end-user to sort, page, and edit its data. But it comes at a cost of speed. Second the display format is simple that is in row and columns. Real life scenarios can be more demanding that.

    With its templates, the DataList provides more control over the look and feel of the displayed data than the DataGrid. It offers better performance than DataGrid.

    Repeater control allows for complete and total control. With the Repeater, the only HTML emitted are the values of the databinding statements in the templates along with the HTML markup specified in the templates—no "extra" HTML is emitted, as with the DataGrid and DataList. By requiring the developer to specify the complete generated HTML markup, the Repeater often requires the longest development time. But repeater does not provide editing features like datagrid so everything has to be coded by programmer. However, the Repeater does boast the best performance of the three data Web controls. Repeater is fastest followed by DataList and finally DataGrid.

  31. Explain main differences between ASP and ASP.NET?

    ASP.NET supports new features:

    Better Language Support

    • New ADO.NET Concepts have been implemented.
    • ASP.NET supports full language (C#, VB.NET, C++) and not simple scripting like Vbscript.

    Better controls than ASP

    • ASP.NET covers large sets of HTML controls.
    • Better Display grid like Datagrid, Repeater and DataList. Many of the display grids have paging support.

    Compiled Code

    • The first request for an ASP.NET page on the server will compile the ASP.NET code and keep a cached copy in memory. The result of this is greatly increased performance.
    • Better Display grid like Datagrid, Repeater and DataList. Many of the display grids have paging support.

    Controls have events support

    • All ASP.NET controls support events.
    • Load, Click and Change events handled by code makes coding much simpler and much better organized.

    Compiled Code

    • The first request for an ASP.NET page on the server will compile the ASP.NET code and keep a cached copy in memory. The result of this is greatly increased performance.

    Better Authentication Support

    • ASP.NET supports forms-based user authentication, including cookie management and automatic redirecting of unauthorized logins. (You can still do your custom login page and custom user checking).

    User Accounts and Roles

    • ASP.NET allows for user accounts and roles, to give each user (with a given role) access to different server code and executables.

    High Scalability

    • Server to server communication has been greatly enhanced, making it possible to scale an application over several servers. One example of this is the ability to run XML parsers, XSL transformations and even resource hungry session objects on other servers.

    Easy Configuration

    • Configuration of ASP.NET is done with plain text files.
    • Configuration files can be uploaded or changed while the application is running. No need to restart the server, deal with metabase or registry.

    Easy Deployment

    • No more server restart to deploy or replace compiled code. ASP.NET simply redirects all new requests to the new code.

  32. What are major events in GLOBAL.ASAX file ?

    The Global.asax file, which is derived from the HttpApplication class, maintains a pool of HttpApplication objects, and assigns them to applications as needed. The Global.asax file contains the following events

    Application_Init: Fired when an application initializes or is first called. It is invoked for all HttpApplication object instances.

    Application_Disposed: Fired just before an application is destroyed. This is the ideal
    location for cleaning up previously used resources.

    Application_Error: Fired when an unhandled exception is encountered within the application.

    Application_Start: Fired when the first instance of the HttpApplication class is created. It allows you to create objects that are accessible by all HttpApplication instances.

    Application_End: Fired when the last instance of an HttpApplication class is destroyed. It is fired only once during an application’s lifetime.

    Application_BeginRequest: Fired when an application request is received. It is the first event fired for a request, which is often a page request (URL) that a user enters.

    Application_EndRequest: The last event fired for an application request.

    Application_PreRequestHandlerExecute: Fired before the ASP.NET page framework begins executing an event handler like a page or Web service.

    Application_PostRequestHandlerExecute: Fired when the ASP.NET page framework has finished executing an event handler.

    Application_PreSendRequestHeaders: Fired before the ASP.NET page framework sends HTTP headers to a requesting client (browser).

    Application_PreSendContent: Fired before the ASP.NET page framework send content to a requesting client (browser).(browser).

    Application_AcquireRequestState:Fired when the ASP.NET page framework gets the current state (Session state) related to the current request.

    Application_ReleaseRequestState:Fired when the ASP.NET page framework completes execution of all event handlers. This results in all state modules to save their current state data.

    Application_ResolveRequestCache: Fired when the ASP.NET page framework completes an authorization request. It allows caching modules to serve the request from the cache, thus bypassing handler execution.

    Application_UpdateRequestCache:Fired when the ASP.NET page framework completes handler execution to allow caching modules to store responses to be used to handle subsequent requests.

    Application_AuthenticateRequest: Fired when the security module has established the current user’s identity as valid. At this point, the user’s credentials have been validated.

    Application_AuthorizeRequest: Fired when the security module has verified that a user can access resources.

    Session_Start: Fired when a new user visits the application Web site.

    Session_End:Fired when a user’s session times out, ends, or they leave the application Web site.

  33. What order they are triggered?

    They’re triggered in the following order:

    • Application_BeginRequest
    • Application_AuthenticateRequest
    • Application_AuthorizeRequest
    • Application_ResolveRequestCache
    • Application_AcquireRequestState
    • Application_PreRequestHandlerExecute
    • Application_PreSendRequestHeaders
    • Application_PreSendRequestContent
    • ..code is executed..
    • Application_PostRequestHandlerExecute
    • Application_ReleaseRequestState
    • Application_UpdateRequestCache
    • Application_EndRequest
February 8, 2008 | Posted Under ASP.Net Interview Questions, Interview Questions 

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