How to use SPLongOperation in Page_Load for Visual WebPart

 I am using the Following Code

SPLongOperation.Begin(
    delegate(SPLongOperation longOperation)
    {
        // Do something that takes a long time to complete.

         // Inform the server that the work is done
        // and that the page used to indicate progress
        // is no longer needed.
        longOperation.End("EndPage.aspx");
        //longOperation.Dispose();
       
    }
);

I Dont have "EndPage.aspx" I want to use this Code in the Page Load

if I remove the code  longOperation.End("EndPage.aspx");

its work fine except the loading window still there its never disappear even if I use longOperation.Dispose();

any help please

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