BackgroundWorker.CancellationPending Eigenschaft

  • Referenz

Definition

Namespace:
System.ComponentModel
Assemblys:
System.dll, System.ComponentModel.EventBasedAsync.dll
Assembly:
System.ComponentModel.EventBasedAsync.dll
Assembly:
System.dll
Assembly:
netstandard.dll

Ruft einen Wert ab, der angibt, ob die Anwendung den Abbruch eines Hintergrundvorgangs angefordert hat.

public:
 property bool CancellationPending { bool get(); };
public bool CancellationPending { get; }
[System.ComponentModel.Browsable(false)]
public bool CancellationPending { get; }
member this.CancellationPending : bool
[<System.ComponentModel.Browsable(false)>]
member this.CancellationPending : bool
Public ReadOnly Property CancellationPending As Boolean

Eigenschaftswert

Boolean

true, wenn die Anwendung den Abbruch eines Hintergrundvorgangs angefordert hat, andernfalls false. Der Standardwert ist false.

Attribute
BrowsableAttribute

Beispiele

Im folgenden Codebeispiel wird die Verwendung der CancellationPending Eigenschaft veranschaulicht, um einen BackgroundWorker Abbruchzustand abzufragen. Dieses Codebeispiel ist Teil eines größeren Beispiels, das für die BackgroundWorker Klasse bereitgestellt wird.

// Abort the operation if the user has cancelled.
// Note that a call to CancelAsync may have set 
// CancellationPending to true just after the
// last invocation of this method exits, so this 
// code will not have the opportunity to set the 
// DoWorkEventArgs.Cancel flag to true. This means
// that RunWorkerCompletedEventArgs.Cancelled will
// not be set to true in your RunWorkerCompleted
// event handler. This is a race condition.
if ( worker->CancellationPending )
{
   e->Cancel = true;
}
else
{
   if ( n < 2 )
   {
      result = 1;
   }
   else
   {
      result = ComputeFibonacci( n - 1, worker, e ) + ComputeFibonacci( n - 2, worker, e );
   }

   // Report progress as a percentage of the total task.
   int percentComplete = (int)((float)n / (float)numberToCompute * 100);
   if ( percentComplete > highestPercentageReached )
   {
      highestPercentageReached = percentComplete;
      worker->ReportProgress( percentComplete );
   }
}

// Abort the operation if the user has canceled.
// Note that a call to CancelAsync may have set 
// CancellationPending to true just after the
// last invocation of this method exits, so this 
// code will not have the opportunity to set the 
// DoWorkEventArgs.Cancel flag to true. This means
// that RunWorkerCompletedEventArgs.Cancelled will
// not be set to true in your RunWorkerCompleted
// event handler. This is a race condition.

if (worker.CancellationPending)
{   
    e.Cancel = true;
}
else
{   
    if (n < 2)
    {   
        result = 1;
    }
    else
    {   
        result = ComputeFibonacci(n - 1, worker, e) + 
                 ComputeFibonacci(n - 2, worker, e);
    }

    // Report progress as a percentage of the total task.
    int percentComplete = 
        (int)((float)n / (float)numberToCompute * 100);
    if (percentComplete > highestPercentageReached)
    {
        highestPercentageReached = percentComplete;
        worker.ReportProgress(percentComplete);
    }
}

' Abort the operation if the user has canceled.
' Note that a call to CancelAsync may have set 
' CancellationPending to true just after the
' last invocation of this method exits, so this 
' code will not have the opportunity to set the 
' DoWorkEventArgs.Cancel flag to true. This means
' that RunWorkerCompletedEventArgs.Cancelled will
' not be set to true in your RunWorkerCompleted
' event handler. This is a race condition.
If worker.CancellationPending Then
    e.Cancel = True
Else
    If n < 2 Then
        result = 1
    Else
        result = ComputeFibonacci(n - 1, worker, e) + _
                 ComputeFibonacci(n - 2, worker, e)
    End If

    ' Report progress as a percentage of the total task.
    Dim percentComplete As Integer = _
        CSng(n) / CSng(numberToCompute) * 100
    If percentComplete > highestPercentageReached Then
        highestPercentageReached = percentComplete
        worker.ReportProgress(percentComplete)
    End If

End If

Hinweise

If CancellationPending is , then the CancelAsync method has be aufruf on the BackgroundWorker.true

Diese Eigenschaft ist für die Verwendung durch den Arbeitsthread gedacht, was regelmäßig überprüft CancellationPending und abgebrochen werden soll, wenn er auf true"festgelegt" festgelegt ist.

Gilt für

Siehe auch