AsyncOperationManager.CreateOperation Method

Parameters

• userSuppliedState
  Type: System.Object
  An object that is used to associate a piece of client state, such as a task ID, with a particular asynchronous operation.

Return Value

Type: System.ComponentModel.AsyncOperation
An AsyncOperation that you can use to track the duration of an asynchronous method invocation.

    ' Start GetPersons as an asynchronous process. 
    Public Sub GetPersonsAsync(ByVal itemsCount As Integer, _
                               ByVal name As String, _
                               ByVal taskId As Object)

        Dim asyncOp As AsyncOperation

        ' First make sure this is not an attempt to start the 
        ' same thread twice. Multiple threads will access the 
        ' taskID Dictionary, so it must be locked to serialize 
        ' access. 
        SyncLock Me
            If taskIDs.ContainsKey(taskId) Then
                Throw New ArgumentException _
                    ("Task ID already exists", "taskID")
            End If

            ' Create a new AsyncOperation object 
            ' and put it in the taskID Dictionary. 
            asyncOp = AsyncOperationManager.CreateOperation(taskId)
            taskIDs(taskId) = asyncOp
        End SyncLock

        ' Start the asynchronous process. 
        Dim myThread As New Thread(AddressOf StartThread)
        myThread.Start(New ThreadStartParms With _
             {.ItemsCount = itemsCount, .Name = name, .AsyncOp = asyncOp})

    End Sub

    Private Sub StartThread(ByVal parms As ThreadStartParms)
        GetPersons(parms.ItemsCount, parms.Name, parms.AsyncOp)
    End Sub

// Start GetPersons as an asynchronous process.
public void GetPersonsAsync
    (int itemsCount, string name, object taskId)
{
    AsyncOperation asyncOp;

    // First make sure this is not an attempt to start the 
    // same thread twice.  Multiple threads will access the
    // taskID Dictionary, so it must be locked to serialize
    // access.
    lock (this)
    {
        if (taskIDs.ContainsKey(taskId))
        {
            throw new ArgumentException
                ("Task ID already exists", "taskID");
        }

        // Create a new AsyncOperation object
        // and put it in the taskID Dictionary.
        asyncOp =
            AsyncOperationManager.CreateOperation(taskId);
        taskIDs[taskId] = asyncOp;
    }

    // Start the asynchronous process.
    // The following line is the least amount of code to do 
    // this.  It uses a lambda expression.  Following it is 
    // commented code showing an alternative method.

    new Thread(() =>
        { GetPersons(itemsCount, name, asyncOp); }).Start();

    // The alternative is to include two lines here and
    // define separately the method that they reference and
    // a class you can use to pass parameters to Thread.Start:

    //   Thread myThread = 
    //       new Thread(new ThreadStart(StartThread));
    //   myThread.Start(new ThreadStartParms 
    //       {.ItemsCount=itemsCount, 
    //        .Name=name, 
    //        .AsyncOp=asyncOp });

    //   void StartThread()
    //   {
    //      GetPersons(itemsCount, name, asyncOp);
    //   }

    //   public class ThreadStartParms)
    //   {
    //       public int ItemsCount { get; set; }
    //       public string Name { get; set; }
    //       public AsyncOp AsyncOperation { get; set; }
    //   }

}