Question

Is there any way to redirect from Page_Load (or any other ASP.NET event) when using async–await? Of course Redirect throws ThreadAbortException but even if I catch it with try–catch it ends up with an error page. If I call Response("url", false) it doesn’t crash but I need to stop execution of the page (rendering the page etc.) so it’s not the solution. And as I noticed these two methods act differently:

This ends up with ThreadAbortException (I assume the task ends synchronously):

protected async void Page_Load()
{
    await Task.Run(() => { });
    Response.Redirect("http://www.google.com/");
}

This one continues after Response.Redirect:

protected async void Page_Load()
{
    await Task.Delay(1000);
    Response.Redirect("http://www.google.com/");
}

I must wait for the response but I was experimenting and even if I remove the await keyword (so Task runs in background and the method continues) it ends up the same. Only thing that helps is to remove the async keyword – I thought async ONLY enables await and nothing more?!

Answer 1

OK, I found the answer how to deal with it.

I’ve created a Redirect method wrapper in my base Page class:

protected void Redirect(string url)
{
    this.isRedirecting = true;

    Response.Redirect(url, false);

    if (Context.ApplicationInstance != null)
        Context.ApplicationInstance.CompleteRequest();
}

And override Render and RaisePostBackEvent:

protected override void Render(HtmlTextWriter writer)
{
    if (this.isRedirecting)
        return;
}

protected override void RaisePostBackEvent(IPostBackEventHandler sourceControl, string eventArgument)
{
    if (!this.isRedirecting)
        base.RaisePostBackEvent(sourceControl, eventArgument);
}

That does the trick. ASP.NET 4.5 won’t fire the PreRenderComplete event (= won’t continue in the life-cycle) until all awaited tasks are completed.