AsyncCompletedEventArgs.Error 属性

定义

命名空间:

System.ComponentModel

程序集:

System.ComponentModel.EventBasedAsync.dll

Source:

AsyncCompletedEvent.cs

获取一个值，该值指示异步操作期间发生的错误。

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

public Exception? Error { get; }

member this.Error : Exception

Public ReadOnly Property Error As Exception

属性值

Exception

如果异步操作期间发生错误，则为 Exception 实例；否则为 null。

示例

下面的代码示例演示如何使用 AsyncOperation 来跟踪异步操作的生存期。 此代码示例是为 System.ComponentModel.AsyncOperationManager 类提供的一个更大示例的一部分。

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

注解

如果在异步操作期间引发异常，则 类会将异常 Error 分配给 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 属性;否则，该属性将引发 ，TargetInvocationException其InnerException属性包含对 的Error引用。

如果取消了操作， Error 则 属性 null 的值为 。

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() 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