How to do it...

Follow these steps to update the existing project and to have cancellation support during the long running process:

1. Navigate to the MainWindow.xaml file and modify the UI to have a Cancel button in it. Add the following button control inside StackPanel, and label it as Cancel:

<Button x:Name="cancelButton" 
        Content="Cancel" 
        IsEnabled="False" 
        Margin="4" 
        Padding="8 2" 
        Click="OnCancelClicked"/> 

2. Make sure to set its IsEnabled property to False.
3. Now, navigate to the MainWindow.xaml.cs file and add the following member variable inside the class:

private CancellationTokenSource tokenSource = null; 

4. On the Cancel button click, we need to cancel the running operation. Let's modify the OnCancelClicked event to perform the same as the following code snippet:

private void OnCancelClicked(object sender,  
                             RoutedEventArgs e) 
{ 
    if...