BackgroundWorker.RunWorkerCompleted Событие

Определение

Возникает, когда выполнение фоновой операции завершено, отменено или вызвало исключение.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 

Примеры

В следующем примере кода показано использование события RunWorkerCompleted для управления результатом асинхронной операции.The following code example demonstrates the use of the RunWorkerCompleted event to handle the result of an asynchronous operation. Этот пример кода является частью большого примера, приведенного для класса BackgroundWorker.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

Комментарии

Это событие возникает, когда обработчик событий DoWork возвращает.This event is raised when the DoWork event handler returns.

Если операция завершается успешно и ее результат назначается в обработчике событий DoWork, можно получить доступ к результату через свойство RunWorkerCompletedEventArgs.Result.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.

Свойство Error System.ComponentModel.RunWorkerCompletedEventArgs указывает, что операция была вызвана исключением.The Error property of System.ComponentModel.RunWorkerCompletedEventArgs indicates that an exception was thrown by the operation.

Свойство Cancelled System.ComponentModel.RunWorkerCompletedEventArgs указывает, был ли запрос отмены обработан фоновой операцией.The Cancelled property of System.ComponentModel.RunWorkerCompletedEventArgs indicates whether a cancellation request was processed by the background operation. Если код в обработчике событий DoWork обнаруживает запрос на отмену путем проверки флага CancellationPending и установки флага Cancel для System.ComponentModel.DoWorkEventArgs на true, Cancelled System.ComponentModel.RunWorkerCompletedEventArgs также будет установлено 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.

Внимание!

Имейте в виду, что код в обработчике событий DoWork может завершить свою работу в ходе выполнения запроса на отмену, и ваш цикл опроса может пропускаться CancellationPending заданным значением true.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. В этом случае Cancelled флаг System.ComponentModel.RunWorkerCompletedEventArgs в обработчике событий RunWorkerCompleted не будет установлен в значение true, даже если был сделан запрос на отмену.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. Такая ситуация называется состоянием гонки и является распространенной проблемой в многопоточном программировании.This situation is called a race condition and is a common concern in multithreaded programming. Дополнительные сведения о проблемах многопоточной разработки см. в разделе рекомендации по работе с потоками.For more information about multithreading design issues, see Managed Threading Best Practices.

Обработчик событий RunWorkerCompleted должен всегда проверять свойства AsyncCompletedEventArgs.Error и AsyncCompletedEventArgs.Cancelled, прежде чем обращаться к свойству RunWorkerCompletedEventArgs.Result.Your RunWorkerCompleted event handler should always check the AsyncCompletedEventArgs.Error and AsyncCompletedEventArgs.Cancelled properties before accessing the RunWorkerCompletedEventArgs.Result property. Если было вызвано исключение или операция была отменена, доступ к свойству RunWorkerCompletedEventArgs.Result вызывает исключение.If an exception was raised or if the operation was canceled, accessing the RunWorkerCompletedEventArgs.Result property raises an exception.

Применяется к

Дополнительно