AsyncCompletedEventArgs.Error 属性

定义

获取一个值,该值指示异步操作期间发生的错误。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

属性值

Exception

如果异步操作期间发生错误,则为 Exception 实例;否则为 nullAn Exception instance, if an error occurred during an asynchronous operation; otherwise null.

示例

下面的代码示例演示如何使用 AsyncOperation 跟踪异步操作的生存期。The following code example demonstrates using an AsyncOperation to track the lifetime of asynchronous operations. 此代码示例是为类提供的更大示例的一部分 System.ComponentModel.AsyncOperationManagerThis 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

注解

如果在异步操作过程中引发了异常,则类会将异常分配给 Error 属性。If an exception is raised during an asynchronous operation, the class will assign the exception to the Error property. 客户端应用程序的事件处理程序委托应该 Error 在访问派生自的类中的任何属性之前检查属性 AsyncCompletedEventArgs ; 否则,属性将引发, TargetInvocationExceptionInnerException 属性保存对的引用 ErrorThe 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.

Error如果操作已取消,则属性的值为 nullThe value of the Error property is null if the operation was canceled.

继承者说明

如果在派生类中提供只读属性,请确保 RaiseExceptionIfNecessary() 在属性实现中调用方法。If you provide read-only properties in a derived class, be sure to call the RaiseExceptionIfNecessary() method in your property implementation. 这会阻止客户端访问由于异步操作中的错误而可能无效的属性。This prevents clients from accessing properties that are potentially not valid due to a failure in the asynchronous operation.

适用于

另请参阅