AsyncCompletedEventArgs Class
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AsyncCompletedEventArgs Class


Provides data for the MethodNameCompleted event.

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


[HostProtectionAttribute(SecurityAction.LinkDemand, SharedState = true)]
public class AsyncCompletedEventArgs : EventArgs


Obsolete.Initializes a new instance of the AsyncCompletedEventArgs class.

System_CAPS_pubmethodAsyncCompletedEventArgs(Exception, Boolean, Object)

Initializes a new instance of the AsyncCompletedEventArgs class.


Gets a value indicating whether an asynchronous operation has been canceled.


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


Gets the unique identifier for the asynchronous task.


Determines whether the specified object is equal to the current object.(Inherited from Object.)


Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)


Serves as the default hash function. (Inherited from Object.)


Gets the Type of the current instance.(Inherited from Object.)


Creates a shallow copy of the current Object.(Inherited from Object.)


Raises a user-supplied exception if an asynchronous operation failed.


Returns a string that represents the current object.(Inherited from Object.)

If you are using a class that implements the Event-based Asynchronous Pattern Overview, 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.

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.

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;
        bool result = e.IsPrime;

        ListViewItem lvi = UpdateListViewItem(

        if (lvi != null)
            lvi.BackColor = Color.LightGray;
            lvi.Tag = null;

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1

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

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