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Maintaining Scroll Position On Postback

When you visit a webpage you have come across a scenario in which vertical dimensions of the web page exceeds those of the browser window. In that case vertical scroll bar appears. When you do some activity on the page that causes the page to post back then the scroll position again resets to the top of the page. To avoid this situation .net has introduced a property called MaintainScrollPositionOnPostback in which the scroll position of browser is maintained in case of post backs.

In this article the main aim is to show you the method by which scroll position is maintained.

When the property MaintainScrollPositionOnPostback is set to true then 2 hidden fields _SCROLLPOSITIONX and _SCROLLPOSITIONY are added on the page. These 2 fields are for maintaining the horizontal and vertical scroll positions during post back.

<input type="hidden" name="__SCROLLPOSITIONX" id="__SCROLLPOSITIONX" value="0" />
<input type="hidden" name="__SCROLLPOSITIONY" id="__SCROLLPOSITIONY" value="0" />

During the post back the property MaintainScrollPositionOnPostback emits a script that invokes the function WebForm_SaveScrollPositionOnSubmit().This function sets current browsers X andY scroll positions to _SCROLLPOSITIONX and _SCROLLPOSITIONY hidden variable before the browser submits the form. When the control returns back to the page a client side method WebForm_RestoreScrollPosition() is called to assign the value of _SCROLLPOSITIONX and _SCROLLPOSITIONY to X and Y.

Posted By -	Karan Gupta

Posted On -	Tuesday, August 10, 2010

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