AsyncCompletedEventArgs
Class
Definition
Provides data for the MethodNameCompleted event.
public class AsyncCompletedEventArgs : EventArgs
- Inheritance
- Derived
Inherited Members
System.EventArgs
System.Object
Examples
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 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
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
Remarks
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 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.
Constructors
| AsyncCompletedEventArgs() |
Initializes a new instance of the AsyncCompletedEventArgs class. |
| AsyncCompletedEventArgs(Exception, Boolean, Object) |
Initializes a new instance of the AsyncCompletedEventArgs class. |
Properties
| Cancelled |
Gets a value indicating whether an asynchronous operation has been canceled. |
| Error |
Gets a value indicating which error occurred during an asynchronous operation. |
| UserState |
Gets the unique identifier for the asynchronous task. |
Methods
| RaiseExceptionIfNecessary() |
Raises a user-supplied exception if an asynchronous operation failed. |