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New Message on MumbaiUserGroup
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From: Swapnil_B1
Message 1 in Discussion
Cross Page PostBack
By default, button controls in ASP.NET pages post back to the same page that
contains the button, where you can write an event handler for the post. In most
cases this is the desired behavior, but occassionaly you will also want to be
able to post to another page in your application. The Server.Transfer method
can be used to move between pages, however the URL doesn't change. Instead, the
cross page posting feature in ASP.NET 2.0 allows you to fire a normal postback
to a different page in the application. In the target page, you can then access
the values of server controls in the source page that initiated the post back.
To use cross page posting, you can set the PostBackUrl property of a Button,
LinkButton or ImageButton control, which specifies the target page. In the
target page, you can then access the PreviousPage property to retrieve values
from the source page. By default, the PreviousPage property is of type Page, so
you must access controls using the FindControl method. You can also enable
strongly-typed access to the source page by setting the @PreviousPageType
directive in the target page to the virtual path or Type name of the source
page. Note that if you intend for multiple pages to post to a single target
page, you cannot use the strongly-typed accessor (leave the PreviousPage
directive unset).
Cross page posting works by the following technique:
Cross page posting sets action of the form in Page 1
When the Button is clicked, the post goes from Page 1 to Page 2
Page 2 retains viewstate from Page 1
When PreviousPage accessed, viewstate is re-populated to an instance of Page 1
Page 1 then executes up to its LoadComplete phase (excludes rendering)
At this point, Page 2 may access the values of controls in Page 1
Because Page 1 will execute (up to LoadComplete) in response to a cross-page
post, it is sometimes necessary to special-case code in the page to only
execute when the request is not a cross-page post, but a normal request to Page
1 instead. You may use the IsCrossPagePostBack property in Page 1 to handle
this situation.
If Not Page.IsCrossPagePostBack Then
' handle a normal request
End If
You can also post back to another application, however the PreviousPage
property is null in this case. You can also transfer in code, while still
preserving viewstate through the PreviousPage property using
Server.Transfer(IHttpHandler, preserveViewState).
Swapnil (Swaps)
http://swapsnet.spaces.live.com/
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