ASP.NET Question/Answer Set-1

ASP.NET
1.1 Whats the difference between Classic ASP and ASP.NET? 

Major difference: Classic ASP is Interpreted. ASP.NET is Compiled. If code is changed, ASP.NET recompiles, otherwise does'nt.
Other differences: ASP works with VB as the language. ASP.NET works with VB.NET & C# as the languages (Also supported by other languages that run on the .NET Framework). 
ASP.NET is the web technology that comes with the Microsoft .NET Framework. The main process in ASP.NET is called aspnet_wp.exe that accesses system resources. ASP.NET was launched in 2002 with version 1.0. Subsequent versions are 1.1 and version 2.0. ASP.NET is built up using thousands of objects, ordered in the System namespace. When an ASP.NET class is compiled, its called an assembly. 
In Classic ASP, complex functionalities are achieved using COM components, that are nothing but component objects created using VB 6, C++ etc, and are usually in a DLL format. These components provide an exposed interface to methods in them, to the objects that reference these components. Last version of classic ASP is version 3.0. ASP has 7 main objects - Application, ASPError, ObjectContext, Request, Response, Server, Session. 

1.2 How to redirect a page to another page? 

The Response object has a famous Redirect method that is used most widely to transfer a web page visitor from one page to another page. 
Syntax of Response.Redirect ...

Response.Redirect("DestinationPage.aspx") 
There is another famous method called Transfer method of the Server object. 
Syntax of Server.Transfer ...

Server.Transfer("DestinationPage.aspx") 

1.3 How to pass values between pages? 

There are several methods to pass values from one page to another page. Described below are few methods to pass values between pages:

QueryString - The QueryString method of passing values between web pages is one of the oldest methods of passing values between pages. A variable value is properly encoded before it is placed on a querystring. This is to make sure that characters that cause problems (like symbols and spaces) are encoded correctly. See the code below to see how QueryString functionality works.
//Code in InitialPage.aspx
String sString;
sString = Server.UrlEncode("string in InitialPage.aspx");
Response.Redirect("DestinationPage.aspx?Value=" & sString);

//Code in DestinationPage.aspx reads the QueryString
String sString;
sString = Request.QueryString("Value");
Response.Write("Your name is " & sString);

The data in the DestinationPage.aspx in the URL looks like this...

http://www.dotnetuncle.com/DestinationPage.aspx?Value=dotnetUncle 
Context - The context object is used to send values between pages. Its similar to the session object, the difference being that, the Context object goes out of scope when the page is sent to a browser. Example code below shows how to use Context object. 
'InitialPage.aspx stores value in context before sending it
Context.Items("MyData") = "dotnetuncle";
Server.Transfer("DestinationPage.aspx");

'DestinationPage.aspx retrieves the value from InitialPage.aspx's context
String sString;
sString = Context.Items("MyDate").ToString;
Response.Write("The data is as follows: " & sString);
Session - The session object is used to persist data across a user session during the user's visit to a website. It is almost same as the Context object. When we use Response.Redirect, it causes the Context object to go away, so rather the Session object is used in such a scenario. Session object uses more of server memory than a context object. Example code below shows how to use Session object. 
'InitialPage.aspx stores value in session before sending it
Session.Items("MyData") = "dotnetuncle";
Response.Redirect("DestinationPage.aspx");

'DestinationPage.aspx retrieves the value from InitialPage.aspx's session
String sString;
sString = Session.Items("MyDate").ToString;
Response.Write("The data is as follows: " & sString);
You may notice above, I have used Response.Redirect with session object, and server.transfer with a context object.

How do you turn off SessionState in the web.config file? 
In the system.web section of web.config, you should locate the httpmodule tag and you simply disable session by doing a remove tag with attribute name set to session.






1.4 How to sort the contents of a GridView control? 

The ASP.NET 2.0 GridView control is a powerful control, the enables sorting of the rows based on a column, all this possible, without writing code. Well thats what we call power! 

The GridView control relies on the underlying data source control to whom this is bound for the sorting capability. The GridView needs to have an AccessDataSource or an SQlDataSource or an ObjectDataSource (if the SortParameterName property is set to a value allowed. 

The AllowSorting property of the GridView control, when set to true, enables sorting of the GridView. A sortable GridView has the Header column represented as a LinkButton control. When this Link Button is clicked, the Sorting event of the GridView is raised server-side, which causes a postback and in turn, sorts the GridView control's records. 

1.29 What does the Hotspot class in .NET do? What is an ImageMap in ASP.NET?

An ImageMap is an ASP.NET control that allows clicks inside a polygon like (called Hotspot) region in a webpage. Well, that actually means you may create a star-shaped or diamond shaped button. Wow! 

There are several pre-defined shapes allowed inside an ImageMap for which templates may be used. For example, for a rectangle, an asp:RectangularHotSpot may be used. For a circle, an asp:CircleHotSpot may be used. And for creating stars & diamonds, an asp:PolygonHotSpot may be used. An image may also be put in an ImageMap which may be specified by its ImageUrl property. 

In order to invoke an event, the HotSpotMode property needs to be set to PostBack. Further, if several HotSpots are placed inside an ImageMap, the event of the ImageMap may be passed a value using the PostBackValue property. 
Code below shows how to create a Polygon HotSpot using an ImageMap.


ImageUrl="Photo.gif" OnClick="SomeEvent"
AlternateText="Click Here"
HotSpotMode="Navigate">


AlternateText="Click Here Too!"
Coordinates="100,150, 250,350, 210,290, 90,350, 60,240"
NavigateUrl="http://www.asp.net"
Target="_blank"/>

1.30 How do we update and delete data in a gridview? Datakeynames property in .NET? 
The best way to Update or Delete a record in a GridView control is to include a CheckBox column and a Submit Button. 

The GridView has its own Delete and Edit functionality. If the GridView is populated with data using an SqlDataSource, checkout the wizard that comes along with the SqlDataSource. It may be used to automatically create an SQL Delete command and specify the delete parameters. 

The DataKeyNames property of the GridView is set to a field name of the Table. 
1.31 How to add gridview/datagrid columns manually? Autogenerate in .NET? 
The datagrid (of ASP.NET 1.1) and gridview (of ASP.NET 2.0) has a property called AutoGenerateColumns. This property is set to false. After this, columns may be set manually. Sample source below... 

SelectCommand="SELECT [au_id], [au_lname], [au_fname], [phone], [address] FROM [authors]"
ConnectionString="" />