AsyncCompletedEventArgs.UserState AsyncCompletedEventArgs.UserState AsyncCompletedEventArgs.UserState AsyncCompletedEventArgs.UserState Property

Definition

Ruft den eindeutigen Bezeichner der asynchronen Aufgabe ab.Gets the unique identifier for the asynchronous task.

public:
 property System::Object ^ UserState { System::Object ^ get(); };
public object UserState { get; }
member this.UserState : obj
Public ReadOnly Property UserState As Object

Eigenschaftswert

Ein Objektverweis, der die asynchrone Aufgabe eindeutig bezeichnet, andernfalls null, wenn kein Wert festgelegt wurde.An object reference that uniquely identifies the asynchronous task; otherwise, null if no value has been set.

Beispiele

Das folgende Codebeispiel veranschaulicht die Verwendung einer AsyncOperation zum Nachverfolgen der Lebensdauer der asynchronen Vorgänge an.The following code example demonstrates 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 eine Klasse mehrere asynchrone Methoden oder mehrere Aufrufe einer einzigen Methode unterstützt, können Sie bestimmen, welche Aufgabe ausgelöst hat die MethodName Completed Ereignis anhand des Werts, der die UserState Eigenschaft.If a class supports multiple asynchronous methods, or multiple invocations of a single method, you can determine which task raised the MethodNameCompleted event by checking the value of the UserState property. Ihr Code verfolgt müssen diese Token, die als Aufgaben-IDs bezeichnet werden, wie die zugehörigen asynchrone Aufgaben starten und abschließen.Your code will need track these tokens, known as task IDs, as their corresponding asynchronous tasks start and complete.

Der Wert dieser Eigenschaft wird während der ursprüngliche Aufruf der asynchronen Methode festgelegt, die die Aufgabe gestartet.The value of this property is set during the original call to the asynchronous method that started the task.

Gilt für:

Siehe auch