AsyncCompletedEventArgs.Error AsyncCompletedEventArgs.Error AsyncCompletedEventArgs.Error AsyncCompletedEventArgs.Error Property

定義

非同期操作中に発生したエラーを示す値を取得します。Gets a value indicating which error occurred during an asynchronous operation.

public:
 property Exception ^ Error { Exception ^ get(); };
public Exception Error { get; }
member this.Error : Exception
Public ReadOnly Property Error As Exception

プロパティ値

非同期操作中にエラーが発生した場合は Exception インスタンス。それ以外の場合は nullAn Exception instance, if an error occurred during an asynchronous operation; otherwise null.

次のコード例に示しますを使用して、AsyncOperation非同期操作の有効期間を追跡します。The following code example demonstrates using an AsyncOperation to track the lifetime of asynchronous operations. このコード例が示されている例の一部、System.ComponentModel.AsyncOperationManagerクラス。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

注釈

クラスが例外を割り当てる場合は、非同期操作中に例外がスローされます、Errorプロパティ。If an exception is raised during an asynchronous operation, the class will assign the exception to the Error property. クライアント アプリケーションのイベント ハンドラー デリゲートを確認する必要があります、Errorから派生したクラスでプロパティにアクセスする前に、プロパティAsyncCompletedEventArgs、それ以外のプロパティが発生、TargetInvocationExceptionでそのInnerExceptionプロパティの保持、参照Errorします。The client application's event-handler delegate should check the Error property before accessing any properties in a class derived from AsyncCompletedEventArgs; otherwise, the property will raise a TargetInvocationException with its InnerException property holding a reference to Error.

値、Errorプロパティはnull操作が取り消された場合。The value of the Error property is null if the operation was canceled.

注意 (継承者)

派生クラスでの読み取り専用プロパティを指定する場合を呼び出すことを確認する、RaiseExceptionIfNecessary()メソッド、プロパティの実装にします。If you provide read-only properties in a derived class, be sure to call the RaiseExceptionIfNecessary() method in your property implementation. これはクライアントが有効でない可能性のある非同期操作でエラーのためのプロパティにアクセスすることを防ぎます。This prevents clients from accessing properties that are potentially not valid due to a failure in the asynchronous operation.

適用対象

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