BackgroundWorker.RunWorkerCompleted BackgroundWorker.RunWorkerCompleted BackgroundWorker.RunWorkerCompleted BackgroundWorker.RunWorkerCompleted Event

定義

バックグラウンド操作の完了時、キャンセル時、またはバックグラウンド操作によって例外が発生したときに発生します。Occurs when the background operation has completed, has been canceled, or has raised an exception.

public:
 event System::ComponentModel::RunWorkerCompletedEventHandler ^ RunWorkerCompleted;
public event System.ComponentModel.RunWorkerCompletedEventHandler RunWorkerCompleted;
member this.RunWorkerCompleted : System.ComponentModel.RunWorkerCompletedEventHandler 
Public Custom Event RunWorkerCompleted As RunWorkerCompletedEventHandler 

次のコード例は、の使用を示します、RunWorkerCompleted非同期操作の結果を処理するイベントです。The following code example demonstrates the use of the RunWorkerCompleted event to handle the result of an asynchronous operation. このコード例が示されている例の一部、BackgroundWorkerクラス。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.
void backgroundWorker1_RunWorkerCompleted( Object^ /*sender*/, RunWorkerCompletedEventArgs^ e )
{
   // First, handle the case where an exception was thrown.
   if ( e->Error != nullptr )
   {
      MessageBox::Show( e->Error->Message );
   }
   else
   if ( e->Cancelled )
   {
      // Next, handle the case where the user cancelled 
      // 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 = "Cancelled";
   }
   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;
}
// 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;
}
' This event handler deals with the results of the
' background operation.
Private Sub backgroundWorker1_RunWorkerCompleted( _
ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs) _
Handles backgroundWorker1.RunWorkerCompleted

    ' First, handle the case where an exception was thrown.
    If (e.Error IsNot Nothing) Then
        MessageBox.Show(e.Error.Message)
    ElseIf e.Cancelled Then
        ' 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()
    End If

    ' Enable the UpDown control.
    Me.numericUpDown1.Enabled = True

    ' Enable the Start button.
    startAsyncButton.Enabled = True

    ' Disable the Cancel button.
    cancelAsyncButton.Enabled = False
End Sub 'backgroundWorker1_RunWorkerCompleted

注釈

このイベントが発生したときに、DoWorkイベント ハンドラーを返します。This event is raised when the DoWork event handler returns.

操作が正常に完了してでその結果が割り当てられているかどうか、DoWorkイベント ハンドラーを通じて結果をアクセスできる、RunWorkerCompletedEventArgs.Resultプロパティ。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.

ErrorプロパティのSystem.ComponentModel.RunWorkerCompletedEventArgs操作によって例外がスローされたことを示します。The Error property of System.ComponentModel.RunWorkerCompletedEventArgs indicates that an exception was thrown by the operation.

CancelledプロパティのSystem.ComponentModel.RunWorkerCompletedEventArgsキャンセル要求をバック グラウンド操作によって処理されたかどうかを示します。The Cancelled property of System.ComponentModel.RunWorkerCompletedEventArgs indicates whether a cancellation request was processed by the background operation. 場合では、コード、DoWorkイベント ハンドラーをチェックして、キャンセル要求を検出する、CancellationPendingフラグと設定、CancelフラグSystem.ComponentModel.DoWorkEventArgstrueCancelledフラグSystem.ComponentModel.RunWorkerCompletedEventArgsにも設定されますtrue.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.

注意事項

注意してくださいをコードで、DoWorkイベント ハンドラーはキャンセル要求にされていると、ポーリング ループを見逃す可能性がありますが作業を完了可能性がありますCancellationPendingに設定されているtrueします。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. ここで、CancelledフラグSystem.ComponentModel.RunWorkerCompletedEventArgsで、RunWorkerCompletedイベント ハンドラーは設定されませんtrueキャンセル要求が行われた場合でも。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. このような状況と呼ばれる、競合状態はマルチ スレッド プログラミングの一般的な懸念事項とします。This situation is called a race condition and is a common concern in multithreaded programming. マルチ スレッド デザインの詳細については、問題を参照してくださいManaged Threading Best Practicesします。For more information about multithreading design issues, see Managed Threading Best Practices.

RunWorkerCompletedイベント ハンドラーが常に確認する必要があります、AsyncCompletedEventArgs.ErrorAsyncCompletedEventArgs.Cancelledプロパティにアクセスする前に、RunWorkerCompletedEventArgs.Resultプロパティ。Your RunWorkerCompleted event handler should always check the AsyncCompletedEventArgs.Error and AsyncCompletedEventArgs.Cancelled properties before accessing the RunWorkerCompletedEventArgs.Result property. 例外が発生した場合、または、操作が取り消された場合へのアクセス、RunWorkerCompletedEventArgs.Resultプロパティは例外を発生させます。If an exception was raised or if the operation was canceled, accessing the RunWorkerCompletedEventArgs.Result property raises an exception.

適用対象

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