C# Cookbook

7.4. Converting a Synchronous Delegate to an Asynchronous Delegate

Problem

You have determined that one or more delegates invoked synchronously within your application are taking a long time to execute. This delay is making the user interface less responsive to the user. These delegates should be converted to asynchronous delegates.

Solution

A typical synchronous delegate is created in the following manner:

using System;

// The delegate declaration
public delegate void SyncInvoke( );

// The class and method that is invoked through the SyncInvoke delegate
public class TestSyncInvoke
{
    public static void Method1( )
    {
        Console.WriteLine("Invoked Method1");
    }
}

The code to use this delegate is:

public class DelegateUtilities
{
    public void TestSimpleSyncDelegate( )
    {
        SyncInvoke SI = new SyncInvoke(TestSyncInvoke.Method1);
        SI( );
    }
}

This delegate can be called asynchronously on a thread obtained from the thread pool by modifying the code as follows:

public class DelegateUtilities { public void TestSimpleAsyncDelegate( ) { AsyncCallback CB = new AsyncCallback(DelegateCallback); SyncInvoke ASI = new SyncInvoke(TestSyncInvoke.Method1); IAsyncResult AR = ASI.BeginInvoke(CB, null); } // The callback that gets called when Method1 is finished processing private static void DelegateCallback(IAsyncResult iresult) { AsyncResult result = (AsyncResult)iresult; AsyncInvoke ASI = (AsyncInvoke)result.AsyncDelegate; int retVal = ASI.EndInvoke(result); Console.WriteLine("retVal (Callback): " + retVal); } ...