BackgroundWorker.RunWorkerCompleted Event

Occurs when the background operation has completed, has been canceled, or has raised an exception.

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

public event RunWorkerCompletedEventHandler RunWorkerCompleted

This event is raised when the DoWork event handler returns.

If the operation completes successfully and its result is assigned in the DoWork event handler, you can access the result through the RunWorkerCompletedEventArgs.Result property.

The Error property of System.ComponentModel.RunWorkerCompletedEventArgs indicates that an exception was thrown by the operation.

The Cancelled property of System.ComponentModel.RunWorkerCompletedEventArgs indicates whether a cancellation request was processed by the background operation. If your code in the DoWork event handler detects a cancellation request by checking the CancellationPending flag and setting the Cancel flag of System.ComponentModel.DoWorkEventArgs to true, the Cancelled flag of System.ComponentModel.RunWorkerCompletedEventArgs also will be 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.

Your RunWorkerCompleted event handler should always check the AsyncCompletedEventArgs.Error and AsyncCompletedEventArgs.Cancelled properties before accessing the RunWorkerCompletedEventArgs.Result property. If an exception was raised or if the operation was canceled, accessing the RunWorkerCompletedEventArgs.Result property raises an exception.

The following code example demonstrates the use of the RunWorkerCompleted event to handle the result of an asynchronous operation. This code example is part of a larger example provided for the BackgroundWorker class.

// This event handler deals with the results of the 
// background operation. 
private void backgroundWorker1_RunWorkerCompleted(
    object sender, RunWorkerCompletedEventArgs e)
{
    // First, handle the case where an exception was thrown. 
    if (e.Error != null)
    {
        MessageBox.Show(e.Error.Message);
    }
    else if (e.Cancelled)
    {
        // Next, handle the case where the user canceled  
        // the operation. 
        // Note that due to a race condition in  
        // the DoWork event handler, the Cancelled 
        // flag may not have been set, even though 
        // CancelAsync was called.
        resultLabel.Text = "Canceled";
    }
    else
    {
        // Finally, handle the case where the operation  
        // succeeded.
        resultLabel.Text = e.Result.ToString();
    }

    // Enable the UpDown control. 
    this.numericUpDown1.Enabled = true;

    // Enable the Start button.
    startAsyncButton.Enabled = true;

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

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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