The cleanest example I have seen for this feature is by Sergey Akopov.

Sergey implement a jQuery example that works wonderfully! Here is the link to the article. I attached the ZIP file same code, which is on Sergey's site as well.

MaintainScroll.zip (3.01 kb)

Here is a link to a pure JavaScript example (older 2006). I have not tried it out but wanted to save the link as another example.

I had a user control embedded in an ASPX (parent) page as a hidden layer. The control was placed inside of a panel control that was hidden. The parent page would load an show the user control

Once the user completed the work they clicked "Close Window" that would raise an event on the parent page, and  the parent page would hide the hidden layer.

1. User Control (ASCX): Add the following delegates and events

// Delegate declaration  
public delegate void OnButtonClick(string strValue);          
// Event declaration  
public event OnButtonClick btnHandlerEditAccount;

2. User Control (ASCX): Button close event will raise btnHandlerEditAccount causing the parent page to hide the panel with the user control.  

protected void BtnCloseWindow_Click(object sender, EventArgs e)
{
   //Make the parent close the window
   if (btnHandlerEditAccount != null) btnHandlerEditAccount(string.Empty);
            
}

3. Parent Page: Handles btnHandlerEditAccount from the user control.

//Event Handlers to close windows from user controls (place in Page_Load)
UCEditAccountInfo.btnHandlerEditAccount += new EditAccountInfo.OnButtonClick(UCEditAccount_btnHandler);

//Syntax of item above: UserControlName dropped on the page += new Class.NameOfActualUserControl.OnButtonClick(handler created in step 1)

/// 

/// Handle the Window Close on the Edit Account User Control
/// 
protected void UCEditAccount_btnHandler(string strValue)
{
     PnlGrid.Enabled = true;
     PnlAccountEdit.Visible = false;
     ReloadGrid(false);
}

To get the full application path (for example to a folder named Documents) in ASP.NET do the following.

1. If you are on a webpage you can use the request object.

string DocPath = Request.MapPath(@"/Documents/");

2. If you are in a class you can use HTTPContext

string DocPath = HttpContext.Current.Request.MapPath(@"/Documents/");

Result: E:\Development\VS2010\MailMerge\MailMerge\Documents\