AsyncOperation Class

Definition

Tracks the lifetime of an asynchronous operation.

public sealed class AsyncOperation
Inheritance
AsyncOperation

Inherited Members

System.Object

Examples

The following code example demonstrates using an AsyncOperation object to track the lifetime of asynchronous operations. This code example is part of a larger example provided for the AsyncOperationManager class.

For a full code listing, see How to: Implement a Component That Supports the Event-based Asynchronous Pattern. For a full code listing of a client form, see How to: Implement a Client of the Event-based Asynchronous Pattern.

// This method starts an asynchronous calculation. 
// First, it checks the supplied task ID for uniqueness.
// If taskId is unique, it creates a new WorkerEventHandler 
// and calls its BeginInvoke method to start the calculation.
public virtual void CalculatePrimeAsync(
    int numberToTest,
    object taskId)
{
    // Create an AsyncOperation for taskId.
    AsyncOperation asyncOp =
        AsyncOperationManager.CreateOperation(taskId);

    // Multiple threads will access the task dictionary,
    // so it must be locked to serialize access.
    lock (userStateToLifetime.SyncRoot)
    {
        if (userStateToLifetime.Contains(taskId))
        {
            throw new ArgumentException(
                "Task ID parameter must be unique", 
                "taskId");
        }

        userStateToLifetime[taskId] = asyncOp;
    }

    // Start the asynchronous operation.
    WorkerEventHandler workerDelegate = new WorkerEventHandler(CalculateWorker);
    workerDelegate.BeginInvoke(
        numberToTest,
        asyncOp,
        null,
        null);
}
' This method starts an asynchronous calculation. 
' First, it checks the supplied task ID for uniqueness.
' If taskId is unique, it creates a new WorkerEventHandler 
' and calls its BeginInvoke method to start the calculation.
Public Overridable Sub CalculatePrimeAsync( _
    ByVal numberToTest As Integer, _
    ByVal taskId As Object)

    ' Create an AsyncOperation for taskId.
    Dim asyncOp As AsyncOperation = _
        AsyncOperationManager.CreateOperation(taskId)

    ' Multiple threads will access the task dictionary,
    ' so it must be locked to serialize access.
    SyncLock userStateToLifetime.SyncRoot
        If userStateToLifetime.Contains(taskId) Then
            Throw New ArgumentException( _
                "Task ID parameter must be unique", _
                "taskId")
        End If

        userStateToLifetime(taskId) = asyncOp
    End SyncLock

    ' Start the asynchronous operation.
    Dim workerDelegate As New WorkerEventHandler( _
        AddressOf CalculateWorker)

    workerDelegate.BeginInvoke( _
        numberToTest, _
        asyncOp, _
        Nothing, _
        Nothing)

End Sub

Remarks

When you implement a class according to the Event-based Asynchronous Pattern Overview, you may need to track the lifetime of each asynchronous operation invoked on an instance of your class. The AsyncOperation class provides ways to track and report the progress of an asynchronous task.

The following list identifies ways to use an AsyncOperation object:

  • To report progress and interim results to the client, call Post from your asynchronous worker code.

  • To indicate that an asynchronous task has completed, or to cancel a pending asynchronous task, call PostOperationCompleted.

Your class should get an AsyncOperation object for each asynchronous task by calling AsyncOperationManager.CreateOperation when each task starts. To allow the client to distinguish separate asynchronous tasks, AsyncOperationManager.CreateOperation takes a parameter for a unique client-provided token, which becomes the UserSuppliedState property. It can then be used by client code to identify the particular asynchronous task that is raising progress or completion events.

Properties

SynchronizationContext

Gets the SynchronizationContext object that was passed to the constructor.

UserSuppliedState

Gets or sets an object used to uniquely identify an asynchronous operation.

Methods

Finalize()

Finalizes the asynchronous operation.

OperationCompleted()

Ends the lifetime of an asynchronous operation.

Post(SendOrPostCallback, Object)

Invokes a delegate on the thread or context appropriate for the application model.

PostOperationCompleted(SendOrPostCallback, Object)

Ends the lifetime of an asynchronous operation.