C# 4 and .NET 4

event-Based asynchronous Pattern ❘ 539
private void OnWorkCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
this.textBoxResult.Text = "Canceled";
}
else
{
this.textBoxResult.Text = e.Result.ToString();
}
this.buttonCalculate.Enabled = true;
this.buttonCancel.Enabled = false;
this.progressBar.Value = 100;
}
Creating an event-based asynchronous Component
To create a custom component that supports the event-based asynchronous pattern, more work needs to be
done. To demonstrate this with a simple scenario, the class AsyncComponent just returns a converted input
string after a time span, as you can see with the synchronous method LongTask(). To offer asynchronous
support, the public interface provides the asynchronous method LongTaskAsync() and the event
LongTaskCompleted. This event is of type EventHandler, which defines
the parameter types object and LongTaskCompletedEventArgs. LongTaskCompletedEventArgs is a type
created later where the caller can read the result of the asynchronous operation.
In addition, some helper methods such as DoLongTask and CompletionMethod are needed; these are
discussed next.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Threading;
namespace Wrox.ProCSharp.Threading
{
public delegate void LongTaskCompletedEventHandler(object sender,
LongTaskCompletedEventArgs e);
public partial class AsyncComponent: Component
{
private Dictionary userStateDictionary =
new Dictionary();
private SendOrPostCallback onCompletedDelegate;
public event EventHandler LongTaskCompleted;
public AsyncComponent()
{
InitializeComponent();
InitializeDelegates();
}
public AsyncComponent(IContainer container)
{
container.Add(this);
}
InitializeComponent();
InitializeDelegates();
private void InitializeDelegates()
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