AsyncCompletedEventArgs.UserState プロパティ

定義

非同期タスクの一意の識別子を取得します。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

プロパティ値

非同期タスクを一意に識別するオブジェクト参照。値が設定されていない場合は nullAn object reference that uniquely identifies the asynchronous task; otherwise, null if no value has been set.

次のコード例は、AsyncOperation を使用して、非同期操作の有効期間を追跡する方法を示しています。The following code example demonstrates using an AsyncOperation to track the lifetime of asynchronous operations. このコード例は、System.ComponentModel.AsyncOperationManager クラス用に用意されている大規模な例の一部です。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.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

注釈

クラスが複数の非同期メソッドをサポートしている場合、または1つのメソッドを複数回呼び出す場合は、UserState プロパティの値をチェックすることによって、 MethodNameCompleted イベントを発生させたタスクを特定できます。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. コードでは、対応する非同期タスクの開始と完了に応じて、タスク Id と呼ばれるこれらのトークンを追跡する必要があります。Your code will need track these tokens, known as task IDs, as their corresponding asynchronous tasks start and complete.

このプロパティの値は、タスクを開始した非同期メソッドへの最初の呼び出し中に設定されます。The value of this property is set during the original call to the asynchronous method that started the task.

適用対象

こちらもご覧ください