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pages enableEventValidation="true" — Possible Solutions

Debugging an invalid postback error in a SharePoint visual web part with an asp:Repeater and FileUpload inside an UpdatePanel.

#sharepoint#debugging#csharp
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Today I had an error (one of many if you are a developer) and it threw me off a bit.

I’m using a visual web part (VS 2010 with SP 2010) and it has an asp:Repeater with buttons. Testing the buttons gave me:

Invalid postback or callback argument. Event validation is enabled using <pages enableEventValidation="true"/> in configuration or <%@ Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation.

Things That DON’T Work

After a lot of searching, you’ll find the following suggestions — all of which are wrong:

  • Add <pages enableEventValidation="true"/> in the ASCX file — wrong
  • Add <%pages enableEventValidation="true"/%> in the ASCX — wrong
  • Add public void Page_PreInit(...) { Page.EnableEventValidation = false; } — wrong
  • Replace all true with false — wrong

Quick Fix

The only thing you need to do is set EnableViewState="false". 🙂

The More Complex Case

Edit: The above “solution” does fix things, but I discovered later that it won’t help when you want to do special things.

I had an UpdatePanel, inside of it an asp:Repeater, and inside the repeater a FileUpload. That’s a quite different story altogether.

Here’s what worked for me:

  1. Add triggers to the UpdatePanel:
<Triggers>
    <asp:PostBackTrigger ControlID="nameOfYourRepeater" />
</Triggers>

  1. Set EnableViewState="true"

  2. Because I have multiple controls, the ID cannot be the same. Add an ItemDataBound event to your repeater in the code-behind:

var item = (DataRowView)e.Item.DataItem;
var button = (Button)e.Item.FindControl("ID_NAME");
button.CommandArgument = e.Item.ItemIndex.ToString();
button.ID = "ID_NAME" + e.Item.ItemIndex.ToString();

Every control is unique because the ID is controlName + ItemIndex. There are other ways, but remember — you may also need to retrieve the unique control later, so ItemIndex is the easiest approach.

Hope it helps someone!