AsyncCompletedEventArgs Class
Assembly: System (in system.dll)
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.
 Note: |
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| 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. |
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.