C# 4 and .NET 4

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The completion handler OnWorkCompleted() is invoked if the asynchronous method has completed
successfully or if it was canceled. If it was canceled, you cannot access the Result property, because this
throws an InvalidOperationException with the information that the operation has been canceled. So,
you have to check the Cancelled property of RunWorkerCompletedEventArgs and behave accordingly.
private void OnWorkCompleted(object sender,
RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
this.textResult.Text = "Cancelled";
}
else
{
this.textResult.Text = e.Result.ToString();
}
this.buttonCalculate.IsEnabled = true;
this.buttonCancel.IsEnabled = false;
}
Running the application once more, you can cancel the asynchronous progress from the user interface.
enable Progress
To get progress information to the user interface, you must set the BackgroundWorker property
WorkerReportsProgress to true.
With the OnDoWork method, you can report the progress to the BackgroundWorker control with the
ReportProgress() method:
private void OnDoWork(object sender, DoWorkEventArgs e)
{
var t = e.Argument as Tuple;
for (int i = 0; i < 10; i++)
{
Thread.Sleep(500);
backgroundWorker.ReportProgress(i * 10);
if (backgroundWorker.CancellationPending)
{
e.Cancel = true;
return;
}
}
}
e.Result = t.Item1 + t.Item2;
code snippet BackgroundWorkersSample/Window1.xaml.cs
The method ReportProgress() fires the ProgressChanged event of the BackgroundWorker control. This
event changes the control to the UI thread.
Add the method OnProgressChanged() to the ProgressChanged event, and in the implementation
set a new value to the progress bar control that is received from the property ProgressPercentage of
ProgressChangedEventArgs:
private void OnProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.progressBar.Value = e.ProgressPercentage;
}
In the OnWorkCompleted() event handler, the progress bar finally is set to the 100% value:
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