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06.05.2008 at 10:17AM PDT, ID: 23461093
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9.0

How can I load/remove a control during postback without running into "Failed to load viewstate" error?

Asked by bemara57 in Programming for ASP.NET, C# Programming Language, .NET Framework 3.x versions

In the Init of one of my pages, I have a condition that either loads one control or another, depending on what the user posted back. The problem is that if a page starts out with one control, then the postback wants to remove that control and add a different control instead, I get the dreaded error of:

"Failed to load viewstate.
The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request."

So my question is how do I change the control tree during postback? I tried doing a ViewState.Remove(controlID) during the Init, but that didn't work. Below is an example that I'm trying to do. Basically I have a dropdown menu full of file paths. If the file path is a user control (ends in .ascx), then I load it to the page. Otherwise I load the contents of the chosen file to a custom editor control and add that. But the problem is someone can go from user control to plain file and vice-versa during a postback- which causes the failed viewstate error. Anyone know a way to solve this scenario?Start Free Trial 
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protected void Page_Init(object sender, EventArgs e)
{
    if (!Request.Form["__EVENTTARGET"].IsNullOrEmpty())
    {
        if (Request.Form["__EVENTTARGET"] == Globals.FileDropDown.UniqueID)
        {
            Session["file"] = Helpers.GetFormValue(
                Request.Form["__EVENTTARGET"]);                        
        }
    }
 
    if (Path.GetExtension(Session["file"]) == ".ascx")
    {
        Control dynamicContent = LoadControl(Session["file"]);
        dynamicContent.ID = "dynamic_control";
        this.Controls.Add(dynamicContent);
    }
    else
    {
        ContentEditor.Value = Helpers.GetContents(Session["file"]);
        this.Controls.Add(ContentEditor);
    }
}
[+][-]06.05.2008 at 10:28AM PDT, ID: 21721905

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About this solution

Zones: Programming for ASP.NET, C# Programming Language, .NET Framework 3.x versions
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Solution Provided By: SystemExpert
Participating Experts: 2
Solution Grade: A
 
 
[+][-]06.05.2008 at 10:32AM PDT, ID: 21721943

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