Information
The topic you requested is included in another documentation set. For convenience, it's displayed below. Choose Switch to see the topic in its original location.

AsyncCompletedEventArgs.Error Property

Gets a value indicating which error occurred during an asynchronous operation.

Namespace: System.ComponentModel
Assembly: System (in system.dll)

public Exception Error { get; }
/** @property */
public Exception get_Error ()

public function get Error () : Exception

Not applicable.

Property Value

An Exception instance, if an error occurred during an asynchronous operation; otherwise a null reference (Nothing in Visual Basic).

If an exception is raised during an asynchronous operation, the class will assign the exception to the Error property. 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.

The value of the Error property is a null reference (Nothing in Visual Basic) if the operation was canceled.

Notes to Inheritors: If you provide read-only properties in a derived class, be sure to call the RaiseExceptionIfNecessary method in your property implementation. This prevents clients from accessing properties that are potentially not valid due to a failure in the asynchronous operation.

The following code example demonstrates using an AsyncOperation to track the lifetime of asynchronous operations. 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;

	...

        // 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;
                }
            }
        }

import System.*;
import System.Collections.*;
import System.Collections.Specialized.*;
import System.ComponentModel.*;
import System.Data.*;
import System.Drawing.*;
import System.Threading.*;
import System.Windows.Forms.*;


	...

    private void primeNumberCalculator1_CalculatePrimeCompleted(Object sender,
        CalculatePrimeCompletedEventArgs e)
    {
        Guid guid = (Guid)e.get_UserState();
        if (e.get_Cancelled()) {
            String result = "Cancelled";
            ListViewItem lvi = UpdateListViewItem((Guid)e.get_UserState(),
                result);
            if (lvi != null) {
                lvi.set_BackColor(Color.get_Pink());
                lvi.set_Tag(null);
            }
        }
        else {
            if (e.get_Error() != null) {
                String result = "Error";
                ListViewItem lvi = UpdateListViewItem((Guid)e.get_UserState(),
                    result);
                if (lvi != null) {
                    lvi.set_BackColor(Color.get_Red());
                    lvi.set_ForeColor(Color.get_White());
                    lvi.set_Tag(null);
                }
            }
            else {
                boolean result = e.get_IsPrime();
                ListViewItem lvi = UpdateListViewItem((Guid)e.get_UserState(),
                    result, e.get_FirstDivisor());
                if (lvi != null) {
                    lvi.set_BackColor(Color.get_LightGray());
                    lvi.set_Tag(null);
                }
            }
        }
    } //primeNumberCalculator1_CalculatePrimeCompleted

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

XNA Framework

Supported in: 1.0

Community Additions

Show:
© 2014 Microsoft