Call the PostOperationCompleted method to end the lifetime of an asynchronous operation. After this method is called for a particular task, calls to its corresponding AsyncOperation object will raise an exception.

The d parameter wraps the delegate you want your class to call when the task's lifetime ends due to completion, cancellation, or failure of the task. The AsyncOperation object will ensure that your delegate is invoked on the thread or context appropriate for the application model. Your delegate can optionally raise an event that notifies clients that the asynchronous task's lifetime has ended.

The arg parameter is used to pass state information to the completion delegate d. You can use an AsyncOperation object, or an System.ComponentModel..::.AsyncCompletedEventArgs object as the parameter value. Alternatively, if you want to provide additional state storage, you can use an instance of a class you derive from the System.ComponentModel..::.AsyncCompletedEventArgs class.

Inheritors must make the PostOperationCompleted invocation asynchronous, so that class library providers do not need to concern themselves with potential stack overflows if they assume asynchrony but a particular application model happens to be synchronous. The method should be interpreted as an “ending the lifetime” call, meaning the implementation needs to do what is appropriate for the application model. For instance, ASP.NET will decrement its count of outstanding asynchronous operations. This also should put the operation into a state such that any subsequent calls into it will fail, since it has now completed.

For more information about implementing asynchronous classes, see Implementing the Event-based Asynchronous Pattern.

The following code example demonstrates using the PostOperationCompleted method to end the lifetime of an asynchronous operation. This code example is part of a larger example provided for the System.ComponentModel..::.AsyncOperationManager class.

' This method cancels a pending asynchronous operation.
Public Sub CancelAsync(ByVal taskId As Object)

    Dim obj As Object = userStateToLifetime(taskId)
    If (obj IsNot Nothing) Then

        SyncLock userStateToLifetime.SyncRoot

            userStateToLifetime.Remove(taskId)

        End SyncLock

    End If

End Sub

// This method cancels a pending asynchronous operation.
public void CancelAsync(object taskId)
{
    AsyncOperation asyncOp = userStateToLifetime[taskId] as AsyncOperation;
    if (asyncOp != null)
    {   
        lock (userStateToLifetime.SyncRoot)
        {
            userStateToLifetime.Remove(taskId);
        }
    }
}

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