AsyncCompletedEventArgs.Error 属性

public:
 property Exception ^ Error { Exception ^ get(); };

public Exception Error { get; }

public Exception? Error { get; }

member this.Error : Exception

Public ReadOnly Property Error As Exception

属性值

如果 异步操作期间发生错误，则为实例;否则为 < a0/> 。

示例

下面的代码示例演示如何使用跟踪 AsyncOperation 异步操作的生存期。 该代码示例是 System.ComponentModel.AsyncOperationManager 类中的一个较大示例的一部分。

using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
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.
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

注解

如果在异步操作期间引发异常，该类会将异常分配给 Error 该属性。 客户端应用程序的事件处理程序委托应在访问派生自AsyncCompletedEventArgs的类中的任何属性之前检查Error该属性;否则，该属性将引发一个TargetInvocationExceptionInnerException包含其引用Error的属性。

该属性的值 Error 是在 null 取消操作时。

继承者说明

如果在派生类中提供只读属性，请确保在属性实现中调用 RaiseExceptionIfNecessary() 该方法。 这可以防止客户端访问由于异步操作失败而可能无效的属性。

另请参阅

• AsyncCompletedEventHandler
• AsyncOperationManager
• AsyncOperation
• 实现基于事件的异步模式