AsyncCompletedEventArgs.UserState 屬性

定義

命名空間:

System.ComponentModel

組件:

System.ComponentModel.EventBasedAsync.dll

來源:

AsyncCompletedEvent.cs

取得非同步工作的唯一識別項。

public:
 property System::Object ^ UserState { System::Object ^ get(); };

public object? UserState { get; }

member this.UserState : obj

Public ReadOnly Property UserState As Object

屬性值

Object

唯一識別非同步工作的物件參考，如果未設定值，則為 null。

範例

下列程式代碼範例示範如何使用 AsyncOperation 來追蹤異步操作的存留期。 此程式代碼範例是針對 類別提供的較大範例的 System.ComponentModel.AsyncOperationManager 一部分。

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.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

備註

如果類別支援多個異步方法，或單一方法的UserState多個調用，您可以藉由檢查 屬性的值來判斷引發 MethodNameCompleted 事件的工作。 您的程式代碼需要追蹤這些令牌，稱為工作標識符，因為其對應的異步工作會啟動和完成。

這個屬性的值會在啟動工作的異步方法原始呼叫期間設定。

另請參閱

• AsyncCompletedEventHandler
• AsyncOperationManager
• AsyncOperation
• 實作事件架構非同步模式