The following code example demonstrates using the AsyncOperationManager class to create a class that supports asynchronous operations for any application model. It shows how to implement a class that tests a number to determine whether it is prime. This calculation can be time consuming, so it is done on a separate thread. Progress reports, incremental results, and completion notifications are handled by the AsyncOperation class, which ensures that the client's event handlers are called on the proper thread or context.
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 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
// 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);
}