AsyncFileUpload postback causes double upload

Question

I implemented the AsyncFileUpload control on a web page. This web page requires uploaded files to appear in a GridView.
The GridView contains the following columns: "File Name", "Confidential" Check Box, and a "Remove" button to remove the uploaded file.

Since the AsyncFileUpload postback does not do a full page postback, I need to "force" a postback on the OnClientUploadComplete event of the AsyncFileUpload control in order to render the gridview after uploading a file.
In the OnClientUploadCompleteEvent, I use javascript to call __doPostBack. In this postback, I only bind my GridView and display the file information (I don’t re-save the file).

The problem: On the AsyncFileUpload’s first “partial” postback, the file is successfully uploaded, as expected. On the second postback that I force with __doPostBack, the file is re-uploaded.
You can verify this by using Google Chrome, which displays the upload progress. The behaviour is as follows:
- After selecting the file, the progress increments from 0% to 100% and the file is uploaded.
- After this, the __doPostBack executes, and you can see the upload progress increment again from 0% to 100%.

How can I make sure the Gridview is properly populated, but that the file is not uploaded twice?

I attached a sample solution which contains the issue: https://www.yousendit.com/download/MzZFc2ZBNDRrYUN4dnc9PQ

Answer 1

Maybe ugly, but works:

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1) Add a css-hidden asp:Button bellow the asp:AsyncFileUpload AsyncFileUpload1 control.

<asp:Button runat="server" ID="btnClick" Text="Update grid" style="display:none"/>

2) On the Page_Load method, remove the if (Request.Params.Get("__EVENTTARGET") == "UploadPostback") and put its block in a simple else to the previous if.

3) On the AsyncFileUpload1_UploadedComplete function, also remove the if (Request.Params.Get("__EVENTTARGET") != "UploadPostback") line, but leave intact everything that was inside it.

4) Back to the aspx. Put a asp:UpdatePanel outside the grid GridView1.

<asp:UpdatePanel runat="server" UpdateMode="Conditional">
     <Triggers>
         <asp:AsyncPostBackTrigger ControlID="btnClick" EventName="Click" />
     </Triggers>
     <ContentTemplate>

     <asp:GridView ID="GridView1" ...
     YOUR GRID CODE REMAINS THE SAME
     </asp:GridView>

    </ContentTemplate>
</asp:UpdatePanel>

5) The last step is to change the AjaxUploadComplete client-side javascript function to make it trigger the postback. Replace it with the following:

function AjaxUploadComplete() {
    var btnClick = document.getElementById("btnClick");
    btnClick.click();
}

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Any file the user selects is uploaded only once.
All changes here are meant to be made in AjaxUpload.aspx & AjaxUpload.aspx.cs of your AjaxUpload.zip.