BackgroundWorker.CancelAsync Method

Requests cancellation of a pending background operation.

Namespace:  System.ComponentModel
Assembly:  System (in System.dll)

public void CancelAsync()

CancelAsync submits a request to terminate the pending background operation and sets the CancellationPending property to true.

When you call CancelAsync, your worker method has an opportunity to stop its execution and exit. The worker code should periodically check the CancellationPending property to see if it has been set to true.

Caution noteCaution

Be aware that your code in the DoWork event handler may finish its work as a cancellation request is being made, and your polling loop may miss CancellationPending being set to true. In this case, the Cancelled flag of System.ComponentModel.RunWorkerCompletedEventArgs in your RunWorkerCompleted event handler will not be set to true, even though a cancellation request was made. This situation is called a race condition and is a common concern in multithreaded programming. For more information about multithreading design issues, see Managed Threading Best Practices.

The following code example demonstrates the use of the CancelAsync method to cancel an asynchronous ("background") operation. This code example is part of a larger example provided for the BackgroundWorker class.


private void cancelAsyncButton_Click(System.Object sender, 
    System.EventArgs e)
{   
    // Cancel the asynchronous operation.
    this.backgroundWorker1.CancelAsync();

    // Disable the Cancel button.
    cancelAsyncButton.Enabled = false;
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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