AsyncCompletedEventArgs.Cancelled AsyncCompletedEventArgs.Cancelled AsyncCompletedEventArgs.Cancelled AsyncCompletedEventArgs.Cancelled Property

Definition

Ruft einen Wert ab, der angibt, ob ein asynchroner Vorgang abgebrochen wurde.Gets a value indicating whether an asynchronous operation has been canceled.

public:
 property bool Cancelled { bool get(); };
public bool Cancelled { get; }
member this.Cancelled : bool
Public ReadOnly Property Cancelled As Boolean

Eigenschaftswert

true, wenn der Hintergrundvorgang abgebrochen wurde, andernfalls false.true if the background operation has been canceled; otherwise false. Die Standardeinstellung ist false.The default is false.

Beispiele

Im folgenden Codebeispiel wird veranschaulicht, die mit einem AsyncOperation zum Nachverfolgen der Lebensdauer der asynchronen Vorgänge an.The following code example demonstrates the using an AsyncOperation to track the lifetime of asynchronous operations. Dieses Codebeispiel ist Teil eines umfangreicheren Beispiels für die System.ComponentModel.AsyncOperationManager Klasse.This code example is part of a larger example provided for the System.ComponentModel.AsyncOperationManager class.

using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Globalization;
using System.Threading;
using System.Windows.Forms;
Imports System
Imports System.Collections
Imports System.Collections.Specialized
Imports System.ComponentModel
Imports System.Drawing
Imports System.Globalization
Imports System.Threading
Imports System.Windows.Forms
// This event handler updates the ListView control when the
// PrimeNumberCalculator raises the CalculatePrimeCompleted
// event. The ListView item is updated with the appropriate
// outcome of the calculation: Canceled, Error, or result.
private void primeNumberCalculator1_CalculatePrimeCompleted(
    object sender, 
    CalculatePrimeCompletedEventArgs e)
{
    Guid taskId = (Guid)e.UserState;

    if (e.Cancelled)
    {   
        string result = "Canceled";

        ListViewItem lvi = UpdateListViewItem(taskId, result);

        if (lvi != null)
        {
            lvi.BackColor = Color.Pink;
            lvi.Tag = null;
        }
    }
    else if (e.Error != null)
    {
        string result = "Error";

        ListViewItem lvi = UpdateListViewItem(taskId, result);

        if (lvi != null)
        {
            lvi.BackColor = Color.Red;
            lvi.ForeColor = Color.White;
            lvi.Tag = null;
        }
    }
    else
    {   
        bool result = e.IsPrime;

        ListViewItem lvi = UpdateListViewItem(
            taskId, 
            result, 
            e.FirstDivisor);

        if (lvi != null)
        {
            lvi.BackColor = Color.LightGray;
            lvi.Tag = null;
        }
    }
}
' This event handler updates the ListView control when the
' PrimeNumberCalculator raises the CalculatePrimeCompleted
' event. The ListView item is updated with the appropriate
' outcome of the calculation: Canceled, Error, or result.
Private Sub primeNumberCalculator1_CalculatePrimeCompleted( _
    ByVal sender As Object, _
    ByVal e As CalculatePrimeCompletedEventArgs) _
    Handles primeNumberCalculator1.CalculatePrimeCompleted

    Dim taskId As Guid = CType(e.UserState, Guid)

    If e.Cancelled Then
        Dim result As String = "Canceled"

        Dim lvi As ListViewItem = UpdateListViewItem( _
            taskId, _
            result)

        If (lvi IsNot Nothing) Then
            lvi.BackColor = Color.Pink
            lvi.Tag = Nothing
        End If

    ElseIf e.Error IsNot Nothing Then

        Dim result As String = "Error"

        Dim lvi As ListViewItem = UpdateListViewItem( _
            taskId, result)

        If (lvi IsNot Nothing) Then
            lvi.BackColor = Color.Red
            lvi.ForeColor = Color.White
            lvi.Tag = Nothing
        End If
    Else
        Dim result As Boolean = e.IsPrime

        Dim lvi As ListViewItem = UpdateListViewItem( _
            taskId, _
            result, _
            e.FirstDivisor)

        If (lvi IsNot Nothing) Then
            lvi.BackColor = Color.LightGray
            lvi.Tag = Nothing
        End If
    End If

End Sub

Hinweise

Wenn die Cancelled Eigenschaft true, der asynchrone Vorgang wurde unterbrochen.When the Cancelled property is true, the asynchronous operation was interrupted.

Ereignishandlerdelegaten für die Client-Anwendung sollte überprüfen die Cancelled Eigenschaft, bevor Sie Zugriff auf Eigenschaften in einer Klasse abgeleitet AsyncCompletedEventArgsist, andernfalls löst die Eigenschaft eine InvalidOperationException , wenn der asynchrone Vorgang war unterbrochen.The client application's event-handler delegate should check the Cancelled property before accessing any properties in a class derived from AsyncCompletedEventArgs; otherwise, the property will raise an InvalidOperationException if the asynchronous operation was interrupted.

Hinweise für Vererber

Wenn Sie die schreibgeschützten Eigenschaften in einer abgeleiteten Klasse angeben, müssen Sie unbedingt Aufrufen der RaiseExceptionIfNecessary() Methode.If you provide read-only properties in a derived class, be sure to call the RaiseExceptionIfNecessary() method. Dadurch wird verhindert, dass Clients den Zugriff auf Eigenschaften, die möglicherweise nicht aufgrund eines Fehlers bei der asynchrone Vorgang gültig sind.This prevents clients from accessing properties that are potentially not valid due to a failure in the asynchronous operation.

Gilt für:

Siehe auch