Gets a value indicating which error occurred during an asynchronous operation.
Assembly: System (in System.dll)
If an exception is raised during an asynchronous operation, the class will assign the exception to the property. The client application's event-handler delegate should check the 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 .
The value of the property is Nothing 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.
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
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.