Using Delegates in C# Asynchronously

Question

I have the following delegate

delegate void UpdateFileDelegate(long maxFileID);

That I am calling from a WinForms app like so

UpdateFileDelegate FD = new UpdateFileDelegate(ClassInstance.UpdateFile);
FD.BeginInvoke(longIDNumber,null,null);

It runs asynchronously but the question I have is how can I tell when the Method is done executing so I can let the end user know?

Update: Thanks to the recommendations below the following code does the trick. Also this article was helpful in getting me to understand what my code is actually doing.

delegate void UpdateFileDelegate(long maxFileID);
UpdateFileDelegate FB = new UpdateFileDelegate(ClassInstance.UpdateFile);
AsyncCallback callback = new AsyncCallback(this.CallBackMethod);
IAsyncResult result = FB.BeginInvoke(longIDNumber);

private void CallBackMethod(IAsyncResult result)
    {
     AsyncResult delegateResult = (AsyncResult)result;

     UpdateFileDelegate fd = (UpdateFileDelegate)delegateResult.AsyncDelegate;
     fd.EndInvoke(result);
     MessageBox.Show("All Done!");
    }

Answer 1

See Calling Synchronous Methods Asynchronously

The BeginInvoke will return an IAsyncResult, which enables a number of different ways to be aware of when it is done, such as using its AsyncWaitHandle.WaitOne() method. It depends on what you are doing in the meantime.

Or you can pass a delegate for a callback method to BeginInvoke. This is arguably the most powerful strategy, but sometimes is overkill.