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AsyncCompletedEventArgs Class

Provides data for the MethodNameCompleted event.

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

'Declaration
Public Class AsyncCompletedEventArgs
	Inherits EventArgs
'Usage
Dim instance As AsyncCompletedEventArgs

public class AsyncCompletedEventArgs extends EventArgs
public class AsyncCompletedEventArgs extends EventArgs
Not applicable.

If you are using a class that implements the Event-based Asynchronous Pattern, the class will provide a MethodNameCompleted event. If you add an instance of the System.ComponentModel.AsyncCompletedEventHandler delegate to the event, you will receive information about the outcome of asynchronous operations in the AsyncCompletedEventArgs parameter of the corresponding event-handler method.

The client application's event-handler delegate can check the Cancelled property to determine if the asynchronous task was cancelled.

The client application's event-handler delegate can check the Error property to determine if an exception occurred during execution of the asynchronous task.

If the class supports multiple asynchronous methods, or multiple calls to the same asynchronous method, you can determine which task raised the MethodNameCompleted event by checking the value of the UserState property. Your code will need to track these tokens, known as task IDs, as their corresponding asynchronous tasks start and complete.

NoteNote:

The HostProtectionAttribute attribute applied to this class has the following Resources property value: SharedState. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

Notes to Inheritors: Classes that follow the Event-based Asynchronous Pattern can raise events to alert clients about the status of pending asynchronous operations. If the class provides a MethodNameCompleted event, you can use the AsyncCompletedEventArgs to tell clients about the outcome of asynchronous operations. You may want to communicate to clients more information about the outcome of an asynchronous operation than an AsyncCompletedEventArgs accommodates. In this case, you can derive your own class from the AsyncCompletedEventArgs class and provide additional private instance variables and corresponding read-only public properties. Call the RaiseExceptionIfNecessary method before returning the property value, in case the operation was canceled or an error occurred.

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.

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 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

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

System.Object
   System.EventArgs
    System.ComponentModel.AsyncCompletedEventArgs
       Derived Classes

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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
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