在等待委托完成时让UI线程继续运行吗？

Question

In my code I use BeginInvoke to fire off a delegate (to load some config from a file). I want my UI to keep responsive, so I thought doing something like this would work:

  LoadConfig lc = new LoadConfig(doLoadConfig);
  IAsyncResult asyncResult = lc.BeginInvoke(null, null);
  while (!asyncResult.IsCompleted)
  {
    asyncResult.AsyncWaitHandle.WaitOne(500, false);
  }
  asyncResult.AsyncWaitHandle.Close();
  bool bLoadResult = lc.EndInvoke(asyncResult);

Problem is it hangs on the waiting bit. Is there any way for me to wait for my delegate to finish while keeping the UI thread alive (kind of like using async / await in .NET 4.5)?

I'm using .NET 3.5 BTW.

Answer 1

So are callbacks my only option then?

I know it's tempting to use polling with DoEvents , but that'd be wrong. To keep the UI responsive, you need to yield back to the UI thread message loop. Ie, you have to return from current method, and handle the completion event asynchronously (via the callback), when it's fired in the future.

In C# 5.0, there's async/await to solve the callback hell problem. In earlier versions, you could exploit yield keyword, like this .