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Q:
What methods are fired during the page load?
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Init() - when the page is instantiated
Load() - when the page is loaded into server memory
PreRender() - the brief moment before the page is displayed to the user as HTML
Unload() - when page finishes loading.
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Q:
Difference between REsponse.Write() and Response.Output.Write()?
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Response.Output.Write() is capable of writing formatted output.
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Q:
What namespace does the Web page belong in the .NET Framework class hierarchy?
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It is System.Web.UI.Page
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Q:
Where do you store the information about the user’s locale?
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System.Web.UI.Page.Culture
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Q:
What’s a bubbled event?
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When you have a complex control, like DataGrid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid event handler to take care of its constituents.
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Q:
Attach Mouseover event to your ASP .NET control?
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Add an OnMouseOver attribute to the button. Example: btnSubmit.Attributes.Add("onmouseover","someClientCodeHere();");
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Q:
Explain the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe in the page loading process?
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inetinfo.exe is the MS IIS server. All the request are received by the IIS. When an ASP.NET request is received (usually a file with .aspx extension),the ISAPI filter aspnet_isapi.dll takes care of it by passing the request to the actual worker process aspnet_wp.exe.
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Q:
What’s the difference between Response.Write() and Response.Output.Write()?
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Response.Write() is unformatted output where as Response.Output.Write() allows you to write formatted output.
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Q:
What’s the difference between Response.Write() and Response.Output.Write()?
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Response.Write() is unformatted output where as Response.Output.Write() allows you to write formatted output.
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Q:
What are the events which occures during the page load?
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Page Event |
Typical Use |
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PreInit |
Use this event for the following:
· Check the IsPostBack property to determine whether this is the first time the page is being processed.
· Create or re-create dynamic controls.
· Set a master page dynamically.
· Set the Theme property dynamically.
· Read or set profile property values. |
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Init |
Raised after all controls have been initialized and any skin settings have been applied. Use this event to read or initialize control properties. |
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InitComplete |
Raised by the Page object. Use this event for processing tasks that require all initialization be complete. |
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PreLoad |
Use this event if you need to perform processing on your page or control before the Load event.
After the Page raises this event, it loads view state for itself and all controls, and then processes any postback data included with the Request instance. |
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Load |
The Page calls the OnLoad event method on the Page, then recursively does the same for each child control, which does the same for each of its child controls until the page and all controls are loaded.
Use the OnLoad event method to set properties in controls and establish database connections. |
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Control events |
Use these events to handle specific control events, such as a Button control's Click event or a TextBox control's TextChanged event. |
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LoadComplete |
Use this event for tasks that require that all other controls on the page be loaded. |
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PreRender |
Before this event occurs:
· The Page object calls EnsureChildControls for each control and for the page.
· Each data bound control whose DataSourceID property is set calls its DataBind method.
The PreRender event occurs for each control on the page. Use the event to make final changes to the contents of the page or its controls. |
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SaveStateComplete |
Before this event occurs, ViewState has been saved for the page and for all controls. Any changes to the page or controls at this point will be ignored.
Use this event perform tasks that require view state to be saved, but that do not make any changes to controls. |
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Render |
This is not an event; instead, at this stage of processing, the Page object calls this method on each control. All ASP.NET Web server controls have a Render method that writes out the control's markup that is sent to the browser.
If you create a custom control, you typically override this method to output the control's markup. However, if your custom control incorporates only standard ASP.NET Web server controls and no custom markup, you do not need to override the Render method.
A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code. |
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Unload |
This event occurs for each control and then for the page. In controls, use this event to do final cleanup for specific controls, such as closing control-specific database connections.
For the page itself, use this event to do final cleanup work, such as closing open files and database connections, or finishing up logging or other request-specific tasks. |
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Q:
What is the base class of the ASP.NET Page?
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System.Web.UI.Page
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Q:
Where do you store the information about the user’s locale?
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System.Web.UI.Page.Culture
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Q:
What’s a bubbled event?
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When you have a complex control, like DataGrid, writing an event processing routine for each object (cell, button, row, etc.) is quite tedious. The controls can bubble up their eventhandlers, allowing the main DataGrid event handler to take care of its constituents.
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Q:
If you want a certain ASP.NET function executed on MouseOver over a certain button. Where do you add an event handler?
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It’s the Attributes property, the Add function inside that property. So btnSubmit.Attributes.Add("onMouseOver","someClientCode();")
above line would attach the someClientCode(); method to the mouseover Event. someClientCode() should be written in scripting normally java script.
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Q:
Explain the differences between Server-side and Client-side code?
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Server-side code runs on the server. Client-side code runs in the clients’ browser. Normally client side code is written in JavaScript where as server side code is written in High level progamming language such as C#.
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Q:
Should validation (did the user enter a real date) occur server-side or client-side? Why?
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Data validation should happen at client-side. This reduces an additional request to the server to validate the users input.
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Q:
What does the "EnableViewState" property do? Why would I want it on or off?
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It enables the viewstate on the page. It allows the page to save the users input on a form. So by seeting the EnableViewState= true on page and control, control would persists its value in between vairous page post backs.
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Q:
What is the difference between Server.Transfer and Response.Redirect? Why would I choose one over the other?
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Server.Transfer is used to post a form to another page in the same website. Server.Transfer keep the object of the page alive and can be accessed from the transfered page.
Response.Redirect is used to redirect the user to another page or site.
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Q:
What are the purpose of Application_Start and Session_Start events?
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Application_Start event is used to initialize the objects which are shared among all the request. Where as Session_Start event is used to increase the counter of hit, and initialize object which are valid for a session.
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Q:
If I’m developing an application that must accommodate multiple security levels though secure login and my ASP.NET web application is spanned across three web-servers (using round-robin load balancing) what would be the best approach to maintain login-in state for the users?
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Maintain the login state security through a database. All the web server would be maintaining the login state in the common database.
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Q:
Describe the difference between inline and code behind.
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Inline code written along side the html in a page(.aspx page itself). Code-behind is code written in a separate file and referenced by the .aspx page.
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Q:
In which event of the page are the controls fully loaded ?
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Page_load event guarantees that all controls are fully loaded with view state and the current data of the controls.
Controls are also accessed in Page_Init events but you will see that viewstate is not fully loaded during this event. actually in the end of the Page_PreLoad event viewstate before the postaback and current user entered values are loaded into controls.
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Q:
If we want to make sure that no one has tampered with
ViewState, how do we ensure it?
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Using the @Page directive EnableViewStateMac to True.
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Q:
What is the use of @ Register directives ?
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@Register directive informs the compiler of any custom server control added to the
page.
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Q:
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. Example below defined is “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>
in the appsetting user define the key value pair.
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Q:
Where is ViewState information stored ?
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In HTML Hidden Fields called __VIEWSTATE. Viewstate is encrypted and contains the value of all controls in the control tree if the page.
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Q:
What is the use of @ OutputCache directive in ASP.NET?
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It is basically used for caching.
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Q:
How many types of validation controls are provided by
ASP.NET ?
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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
TxtPie 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 UserDefined validation.
ValidationSummary
It displays summary of all current validation errors.
Note:- It's rare that some one will ask step by step all the validation controls. Rather they
will ask for what type of validation which validator will be used. Example in one of the
interviews i was asked how you display summary of all errors in the validation
control...just uttered one word Validation summary.
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Q:
Can you explain what is “AutoPostBack” feature in
ASP.NET ?
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Somecontrol such as Button postback the web page as it is clicked. But some control does not postback such as ComboBox on selecting any value.
If we want the control to automatically postback in case of any event, we will need to
set autopastback 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.
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Q:
How can you enable automatic paging in DataGrid ?
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Following are the points to be done in order to enable paging in DataGrid :
1. Set the “AllowPaging” to true.
2. In PageIndexChanged event set the current pageindex clicked.
Note:- The answers are very short, if you have implemented practically its just a revision. Ttry to implement this functionality.
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Q:
What’s the use of “GLOBAL.ASAX” file ?
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It allows to executing ASP.NET application level events and setting application-level
variables.
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Q:
What is the difference between “Web.config” and
“Machine.Config” ?
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Configuration files are used to control and manage the behavior of a web application.
1. Machine.config
2. Web.config
Machine.Config One
Machine.config file is shared for all ASP.NET's Application. It is only
one on the machine for each version of .NET Framework. If you apply
anything in machine.config file then it is applied on all ASP.NET
applications. Machine.config file is universal on the machine. It can
be located in the %runtime install path%\Config directory.
1. This is automatically installed when you install .NET Framework or Visual Studio. Net.
2. This is also called machine level configuration file.
3. Only one machine.config file exists on a server/computer.
4. This file is at the highest level in the configuration hierarchy
Web.Config
Web.config
file is only for particular ASP.NET application. each ASP.NET
application has different file. One ASP.NET application can have more
than one web.config file. But only one in one folder.
1. This is automatically created when you create an ASP.Net web application project.
2. This is also called application level configuration file or folder level configuration file.
3. This
file inherits setting from the machine.config. If same setting key is
defined in both Machine.Config and Web.config, the Web.Config setting
is used.
Difference Between Machine.config and Web.config
Machine.config is automatically installed when you install .NET Framework or Visual Studio. Net.
Web.config is automatically created when you create an ASP.Net web application project.
Machine.config is called machine level configuration file. Only one machine.config file exists on a server.
Web.config is called application level configuration file.
Machine.config file is at the highest level in the configuration hierarchy.
Web.Config file inherits setting from the machine.config
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Q:
What is a SESSION and APPLICATION object ?
|
Session object store information between HTTP requests for a particular user for perticular session only, while application object are global across users.
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|
Q:
What is the difference between Authentication and authorization?
|
These two concepts seem altogether similar but there is wide range of difference. 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.
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Q:
What is impersonation in ASP.NET ?
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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.
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|
Q:
Can you explain in brief how the ASP.NET authentication
process works?
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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.
Below is how the whole process works:
1. 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.
2. 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.
3. 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.
4. 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.
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Q:
What are the various ways of authentication techniques
in ASP.NET?
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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:
1. <authentication mode=”windows”>
2. <authentication mode=”passport”>
3. <authentication mode=”forms”>
4. 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.
1. 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
2. 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 http://
msdn.microsoft.com/library/default.asp?url=/downloads/list/websrvpass.aps. It includes
full details of implementing passport authentication in your own applications.
3. 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.
a. 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.
b. 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.
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|
Q:
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 =”true”/>
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=”true” 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.
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|
Q:
What’s difference between Datagrid, Datalist and repeater
?
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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.
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> 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.
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|
Q:
From performance point of view how do they rate ?
|
Repeater is fastest followed by Datalist and finally datagrid. DataGrid is slowest.
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|
Q:
What is the method to customize columns in DataGrid?
|
use template column.
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|
Q:
How can we format data inside DataGrid?
|
Use the DataFormatString property.
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|
Q:
How to decide on the design consideration to take a
Datagrid, datalist or repeater ?
|
Many make a blind choice of choosing datagrid directly, but that's not the right way.
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.
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|
Q:
Difference between ASP and ASP.NET?
|
ASP.NET new feature supports are as follows :-
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 set’s of HTML controls..
√ 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
√ Much has been done with ASP.NET to provide greater 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. No more metabase or registry puzzle.
Easy Deployment
No more server restart to deploy or replace compiled code. ASP.NET simply redirects all
new requests to the new code.
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|
Q:
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.
Applcation_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).
206
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.
Note :- During interview you do not have to really cram all these events. But just keep the
basic events in mind
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Q:
What is the order of events occurred in GLOBAL.ASAX?
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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.
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Q:
Do session use cookies ?
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Twist:- How can we make session to not to use cookies ?
Left to the user, you will enjoy to find this answer.
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Q:
How can we force all the validation control to run ?
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Page.Validate
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Q:
How can we check if all the validation control are valid and proper ?
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Using the Page.IsValid() property you can check whether all the validation are done.
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Q:
(A)If client side validation is enabled in your Web page, does
that mean server side code is not run?
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When client side validation is enabled server emit’s JavaScript code for the custom
validators. But note that does not mean that server side checks on custom validators do
not execute. It does this redundant check two times as some of the validators do not
support client side scripting.
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Q:
Which JavaScript file is referenced for validating the
validators at the client side ?
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WebUIValidation.js javascript file installed at “aspnet_client” root IIS directory is used
to validate the validation controls at the client side
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Q:
How to disable client side script in validators?
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Set EnableClientScript to false of the validator control.
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Q:
How can I show the entire validation error message in a
message box on the client side?
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In validation summary set “ShowMessageBox” to true.
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Q:
You find that one of your validation is very complicated
and does not fit in any of the validators, what will you do ?
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Best is to go for CustomValidators. Below is a sample code for a custom validator which
checks that a textbox should not have zero value
<asp:CustomValidator id="CustomValidator1" runat="server"
ErrorMessage="Number not divisible by Zero"
ControlToValidate="txtNumber"
OnServerValidate="ServerValidate"
ClientValidationFunction="CheckZero" /><br>
Input:
<asp:TextBox id="txtNumber" runat="server" />
<script language="javascript">
<!--
function CheckZero(source, args) {
int val = parseInt(args.Value, 10);
if (value==0) {
args.IsValid = false;
}
209
else {
args.IsValid = true;
}
}
// -->
</script>
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Q:
What is Tracing in ASP.NET ?
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Tracing allows us to view how the code was executed in detail.
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Q:
How do we enable tracing ?
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In the @Page directive set Trace property to true.
<%@ Page Trace="true" %>
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Q:
What exactly happens when ASPX page is requested from
Browser?
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Note: - Here the interviewer is expecting complete flow of how an ASPX page is processed
with respect to IIS and ASP.NET engine.
Following are the steps which occur when we request a ASPX page :-
√ The browser sends the request to the webserver. Let us assume that the
webserver at the other end is IIS.
√ Once IIS receives the request he looks on which engine can serve this request.
When I mean engine means the DLL who can parse this page or compile and
send a response back to browser. Which request to map to is decided by file
extension of the page requested.
Depending on file extension following are some mapping
√ .aspx, for ASP.NET Web pages,
√ .asmx, for ASP.NET Web services,
√ .config, for ASP.NET configuration files,
√ .ashx, for custom ASP.NET HTTP handlers,
√ .rem, for remoting resources
√ Etc
You can also configure the extension mapping to which engine can route by using the IIS
engine.
Figure: - 7.1 Following screen shows some IIS mappings
Example an ASP page will be sent to old classic ASP.DLL to compile. While .ASPX
pages will be routed to ASP.NET engine for compilation.
√ As this book mainly will target ASP.NET we will look in to how ASP.NET
pages that is ASPX pages generation sequence occurs. Once IIS passes the
request to ASP.NET engine page has to go through two section HTTP module
section and HTTP handler section. Both these section have there own work
to be done in order that the page is properly compiled and sent to the IIS.
HTTP modules inspect the incoming request and depending on that they can
change the internal workflow of the request. HTTP handler actually compiles
the page and generates output. If you see your machine.config file you will see
following section of HTTP modules
<httpModules>
<add name="OutputCache" type="System.Web.Caching.OutputCacheModule" />
<add name="Session" type="System.Web.SessionState.SessionStateModule" />
<add name="WindowsAuthentication"
type="System.Web.Security.WindowsAuthenticationModule" />
<add name="FormsAuthentication"
type="System.Web.Security.FormsAuthenticationModule" />
<add name="PassportAuthentication"
type="System.Web.Security.PassportAuthenticationModule" />
<add name="UrlAuthorization"
type="System.Web.Security.UrlAuthorizationModule" />
<add name="FileAuthorization"
type="System.Web.Security.FileAuthorizationModule" />
<add name="ErrorHandlerModule" type="System.Web.Mobile.ErrorHandlerModule,
System.Web.Mobile, Version=1.0.5000.0,
Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" /
>
</httpModules>
The above mapping will show which functionality is handled by which Namespace.
Example FormsAthuentication is handled by “System.Web.
Security.FormsAuthenticationModule”. If you look at the web.config section HTTP module
is where authentication and authorization happens.
Ok now the HTTP handler is where the actual compilation takes place and the output is
generated. Following is a paste from HTTP handler section of WEB.CONFIG file.
<httpHandlers>
<add verb="*" path="*.vjsproj" type="System.Web.HttpForbiddenHandler" />
<add verb="*" path="*.java" type="System.Web.HttpForbiddenHandler" />
<add verb="*" path="*.jsl" type="System.Web.HttpForbiddenHandler" />
<add verb="*" path="trace.axd" type="System.Web.Handlers.TraceHandler" />
<add verb="*" path="*.aspx" type="System.Web.UI.PageHandlerFactory" />
<add verb="*" path="*.ashx" type="System.Web.UI.SimpleHandlerFactory" />
...
</httpHandlers>
√ Depending on the File extension handler decides which Namespace will
generate the output. Example all .ASPX extension files will be compiled by
System.Web.UI.PageHandlerFactory
√ Once the file is compiled it will be send back again to the HTTP modules and
from there to IIS and then to the browser.
Figure :- 7.2 IIS flow from various sections.
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Q:
How can we kill a user session ?
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Session.abandon
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Q:
How do you upload a file in ASP.NET ?
|
Just a hint we have to use System.Web.HttpPostedFile class. Please explore more about it.
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Q:
How do I send email message from ASP.NET ?
|
ASP.NET provides two namespaces System.WEB.mailmessage class and System.Web.Mail.Smtpmail class. Just a small homework create a Asp.NET project and
send a email to your self.
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Q:
What are different IIS isolation levels?
|
IIS has three level of isolation:-
LOW (IIS process):- In this main IIS process and ASP.NET application run in same process.
So if any one crashes the other is also affected. Example let’s say (well this is not possible)
I have hosted yahoo, hotmail .amazon and google on a single PC. So all application and
the IIS process runs on the same process. In case any website crashes it affects every one.
Figure: - 7.3 LOW IIS process scenario
Medium (Pooled):- In Medium pooled scenario the IIS and web application run in different
process. So in this case there are two processes process1 and process2. In process1 the IIS
process is running and in process2 we have all Web application running.
Figure: - 7.4 Medium pooled scenario
High (Isolated):-In high isolated scenario every process is running is there own process. In
below figure there are five processes and every one handling individual application. This
consumes heavy memory but has highest reliability.
Figure: - 7.5 High isolation scenario
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Q:
ASP used STA threading model, what is the threading
model used for ASP.NET ?
|
ASP.NET uses MTA threading model.
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|
Q:
What is the use of <%@ page aspcompat=true %>
attribute ?
|
This attribute works like a compatibility option. As mentioned before ASP worked in
STA model and ASP.NET works in MTA model, but what if your ASP.NET application
is using a VB COM component. In order that VB COM runs properly in ASP.NET threading
model we have to set attribute. After defining the ASPCOMPAT directive attribute
ASP.NET pages runs in STA model thus building the compatibility between ASP.NET
and old COM components that does not support MTA model.
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Q:
Explain the differences between Server-side and Clientside
code?
|
Server side code is executed at the server side on IIS in ASP.NET framework, while
client side code is executed on the browser.
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|
Q:
Can you explain Forms authentication in detail ?
|
In old ASP if you where said to create a login page and do authentication you have to do
hell lot of custom coding. But now in ASP.NET that’s made easy by introducing Forms
authentication. So let’s see in detail what form authentication is.
Forms authentication uses a ticket cookie to see that user is authenticated or not. That
means when user is authenticated first time a cookie is set to tell that this user is
authenticated. If the cookies expire then Forms authentication mechanism sends the user
to the login page.
Following are the steps which defines steps for Forms authentication :-
√ Configure Web.config file with forms authentication. As shown below in the
config file you can see we have give the cookie name and loginurl page.
<configuration>
<system.web>
<!-- Other settings omitted. -->
<authentication mode="Forms">
<forms name="logincookies"
loginUrl="login.aspx"
protection="All"
timeout="30"
path="/" />
</authentication>
</system.web>
</configuration>
√ Remove anonymous access to the IIS web application, following are changes
done to web.config file.
<configuration>
<system.web>
<!-- Other settings omitted. -->
<authorization>
<deny users="?" />
</authorization>
</system.web>
</configuration>
√ Create the login page which will accept user information. You will have create
your login page that is the Login.aspx which will actually take the user data.
√ Finally a Small coding in the login button.
Let us assume that the login page has two textboxes Txtname and txtapssword.
Also import System.Web.Security and put the following code in login button
of the page.
If Page.IsValid Then
If FormsAuthentication.Authenticate(txtName.Text, txtPassword.Text) Then
FormsAuthentication.RedirectFromLoginPage(txtName.Text, False)
Else
lblStatus.Text = "Error not proper user"
End If
End If
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|
Q:
How do I sign out in forms authentication ?
|
FormsAuthentication.
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|
Q:
If cookies are not enabled at browser end does form
Authentication work?
|
No, it does not work.
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|
Q:
How to use a checkbox in a datagrid?
|
Twist :- How can I track event in checkbox which is one of the columns of a datagrid ?
Note: - This is normally asked when the interviewer want to see that have you really
worked practically on a project.
Following are the steps to be done :-
√ In ASPX page you have to add Itemtemplate tag in datagrid.
<ItemTemplate>
<asp:CheckBox id="CheckBox1" runat="server" AutoPostBack="True"
OnCheckedChanged="Check_Clicked"></asp:CheckBox>
</ItemTemplate>
√ If you look at the Itemtemplate we have “OnCheckChanged” event. This
“OnCheckChanged” event has “Check_Clicked” subroutine is actually in
behind code. Note this method which is in behind code should either be
“protected” or “public”
√ Following below is the subroutine which defines the method
Protected Sub Check_Clicked(ByVal sender As Object, ByVal e As EventArgs)
‘ do something
End Sub
The above steps should be defined in short to the interviewer which will give a quick
feeling of your practical experience with ASP.NET
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|
Q:
What is the difference between “Web farms” and “Web garden”?
|
“Web farms” are used to have some redundancy to minimize failures. It consists of two or
more web server of the same configuration and they stream the same kind of contents.
When any request comes there is switching / routing logic which decides which web
server from the farm handles the request. For instance we have two servers “Server1”
and “Server2” which have the same configuration and content. So there is a special switch
which stands in between these two servers and the users and routes the request accordingly.
Figure 7.7 : - Web Farm in action
Above figure explains in detail how web farm work. You can see there is a router in
between which takes a request and sees which one of the server is least loaded and
forwards the request to that server. So for request1 it route’s server1, for request2 it
routes server2, for request3 it routes to server3 and final request4 is routed to server4. So
you can see because we have web farm at place server1 and server2 are loaded with two
request each rather than one server loading to full. One more advantage of using this
kind of architecture is if one of the servers goes down we can still run with the other
server thus having 24x7 uptime.
The routing logic can be a number of different options:-
√ Round-robin: Each node gets a request sent to it “in turn”. So, server1 gets a request,
then server2 again, then server1, then server2 again. As shown in the above figure.
√ Least Active: Whichever node show to have the lowest number of current connects
gets new connects sent to it. This is good to help keep the load balanced between
the server nodes.
√ Fastest Reply: Whichever node replies faster is the one that gets new requests. This
is also a good option - especially if there are nodes that might not be “equal” in
performance. If one performs better than the other, then send more requests
there rather than which is moving slowly?
Before we try to understand what a web garden is let’s try to understand how IIS handles
processes. All requests to IIS are routed to “aspnet_wp.exe” for IIS 5.0 and “w3wp.exe”
for IIS 6.0. In normal case i.e. with out web garden we have one worker process instance
(“aspnet_wp.exe” / “w3wp.exe”) across all requests. This one instance of worker process
uses the CPU processor as directed by the operating system.
Figure 7.8 : - With out Web Garden
But when we enable web garden for a web server it creates different instances of the
worker process and each of these worker process runs on different CPU. You can see in
the below diagram we have different worker process instances created which run on
different CPU’s.
Figure 7.9 : - With Web Garden
In short we can define a model in which multiple processes run on multiple CPUs in a
single server machine are known as a Web garden.
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|
Q:
How do we configure “WebGarden”?
|
“Web garden” can be configured by using process model settings in “machine.config” or
“Web.config” file. The configuration section is named <processModel> and is shown in
the following example. The process model is enabled by default (enable=”true”). Below
is the snippet from config file.
<processModel
enable=”true”
timeout=”infinite”
idleTimeout=”infinite”
shutdownTimeout=”0:00:05"
requestLimit=”infinite”
requestQueueLimit=”5000"
memoryLimit=”80"
webGarden=”false”
cpuMask=”12"
userName=””
password=””
logLevel=”errors”
clientConnectedCheck=”0:00:05"
/>
From the above processmodel section for web garden we are concerned with only two
attributes “webgarden” and “cpuMask”.
webGarden :- Controls CPU affinity. True indicates that processes should be affinitized
to the corresponding CPU. The default is False.
cpuMask:- Specifies which processors on a multiprocessor server are eligible to run
ASP.NET processes. The cpuMask value specifies a bit pattern that indicates the CPUs
eligible to run ASP.NET threads. ASP.NET launches one worker process for each eligible
CPU. If webGarden is set to false, cpuMask is ignored and only one worker process will
run regardless of the number of processors in the machine. If webGarden is set to true,
ASP.NET launches one worker process for each CPU that corresponds to a set bit in
cpuMask. The default value of cpuMask is 0xffffffff.
Below are detail steps of how to implement web garden
√ click Start and then click Run.
√ type calc.exe and then click OK.
√ Goto View menu, click Scientific.
√ Goto View menu, click Binary.
√ Use 0 and 1 to specify the processors ASP.NET can or cannot use.
Use 1 for the processor that you want to use for ASP.NET. Use 0 for the processor that
you do not want to use for ASP.NET. For example, if you want to use the first two
processors for ASP.NET of a four-processor computer, type 1100.
√ On the View menu, click Decimal. Note the decimal number.
√ Open the Web.config or machine.config file in a text editor such as Notepad. The
Web.config file is located in the folder where the application is saved.
√ In the Web.config file, add the processModel configuration element under the
System.web element. Before adding <processModel> to Web.config file, the user
has to make sure that the allowDefinition attribute in the <processModel> section o f
the Web.config file is set to everywhere.
√ Add and then set the webGarden attribute of the processModel element to True.
√ Add and then set the cpuMask attribute of the processModel element to the result
that is determined in your calculation.
Do not preface the number with 0x because the result of the calculation is a decimal
number. The following example demonstrates the processModel element that is configured
to enable only the first two processors of a four-processor computer.
<processModel
enable=”true”
webGarden=”true”
cpuMask=”12" />
Save the Web.config file.
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|
Q:
What is the main difference between Gridlayout and
FlowLayout ?
|
GridLayout provides absolute positioning for controls placed on the page. Developers
that have their roots in rich-client development environments like Visual Basic will find
it easier to develop their pages using absolute positioning, because they can place items
exactly where they want them. On the other hand, FlowLayout positions items down the
page like traditional HTML. Experienced Web developers favor this approach because it
results in pages that are compatible with a wider range of browsers.
If you look in to the HTML code created by absolute positioning you can notice lot of
DIV tags. While in Flow layout you can see more of using HTML table to position elements
which is compatible with wide range of browsers.
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