Having an IAsyncResult fire a "completed" event

Question

I'm using Remoting to perform some IPC communication, and have the following question:

When I invoke delegates to gather data server-side, it is possible to have an event fired on the client when an IAsyncResult is gathered?

The following code is in VC++, but .net code is .net code.

  GetFileTextDelegate ^svd = gcnew GetFileTextDelegate(obj, &BaseRemoteObject::GetFileText);
  IAsyncResult        ^arValSet = svd->BeginInvoke(nullptr, nullptr);
  String ^result = svd->EndInvoke(arValSet);

In this example, the last line of code will just lock the current thread until the Invoke is completed. Is it possible to just subsbribe to a "IAsyncResult_Completed" event, or something similar?

Thanks

Answer 1

Yes, there's a good example on MSDN of using the AsyncCallback delegate to do this.

The easiest way to do this, is that use BeginInvoke on a delegate and pass it an instance of an AsynCallback delegate to invoke when the operation completes.

In C# (which I'm more familiar with than managed C++) you would basically write:

// when the async operation completes, YourCallBackMethod will be run
AsyncCallback callback = new AsynCallback( YourCallBackMethod );
callAsynchronously.BeginInvoke( callback, null );

In your callback method you must call EndInvoke() on the delegate which you ran asynchronously. The easiest way to do this is to use the supplied IAsyncResult.

Answer 2

You should be able to pass a delegate (AsyncCallBack) to your BeginInvoke, which will execute when the async method has finished executing.

Here is a simple, but straightforward example:

using System;
using System.Threading;
using System.Runtime.Remoting.Messaging;

class MainClass
{
  delegate int MyDelegate(string s);

  static void Main(string[] args)
  {
    MyDelegate X = new MyDelegate(DoSomething);
    AsyncCallback cb = new AsyncCallback(DoSomething2);
    IAsyncResult ar = X.BeginInvoke("Hello", cb, null);

    Console.WriteLine("Press any key to continue");
    Console.ReadLine();
  }
  static int DoSomething(string s)
  {
    Console.WriteLine("doooooooooooooooo");
    return 0;
  }

  static void DoSomething2(IAsyncResult ar)
  {
    MyDelegate X = (MyDelegate)((AsyncResult)ar).AsyncDelegate;
    X.EndInvoke(ar);
  }
}