任務延續以保持UI線程響應

Question

我在WinForms中使用任務從我的UI線程中刪除昂貴的方法。在我的updateComplete和updateFailed任務中，我必須將_updateMessageTaskInProgress設置爲false並啓用我的控件。有沒有什麼辦法可以在一個單獨的任務中完成這個任務，一旦完成任務，updateComplete或updateFailed就會繼續執行（因爲我目前有重複的代碼）？另外，有沒有更好的實現_updateMessageTaskInProgress的方法 - 我不想同時運行多個任務。

private void PerformUpdate() 
{ 
    if (!_updateMessageTaskInProgress) 
     { 
      LoadButton.Enabled = false; 
      MonthEndDateEdit.Enabled = false; 
      BankIssuerListEdit.Enabled = false; 

      Task updateMessages = Task.Factory.StartNew(() => 
      { 
       _updateMessageTaskInProgress = true; 

       ExpensiveMethod(); 
      }); 

      // Task runs when updateMessages completes without exception. Runs on UI thread. 
      Task updateComplete = updateMessages.ContinueWith(update => 
      { 
       DoSuccessfulStuff(); 

       _updateMessageTaskInProgress = false; 
       LoadButton.Enabled = true; 
       MonthEndDateEdit.Enabled = true; 
       BankIssuerListEdit.Enabled = true; 
      }, System.Threading.CancellationToken.None, TaskContinuationOptions.NotOnFaulted, TaskScheduler.FromCurrentSynchronizationContext()); 

      // Task runs when updateMessages completes with exception. Runs on UI thread. 
      Task updateFailed = updateMessages.ContinueWith(task => 
      { 
       DoFailureStuff(); 

       _updateMessageTaskInProgress = false; 
       LoadButton.Enabled = true; 
       MonthEndDateEdit.Enabled = true; 
       BankIssuerListEdit.Enabled = true; 
      }, System.Threading.CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.FromCurrentSynchronizationContext()); 
     } 
} 

Answer 1

我會用這個Event Based Asynchronous-TYPE Pattern。我用分拆法到使用TPL後臺線程的代碼的簡化版本低於

private void TaskSpin(TaskScheduler uiScheduler, 
         Func<TaskScheduler, object[], bool> asyncMethod, 
         object[] methodParameters) 
{ 
    try 
    { 
     Task asyncTask = Task.Factory.StartNew<bool>(() => 
      asyncMethod(uiScheduler, methodParameters)); 

     // Callback for finish/cancellation. 
     asyncTask.ContinueWith(task => 
     { 
      // Check task status. 
      switch (task.Status) 
      { 
       // Handle any exceptions to prevent UnobservedTaskException.    
       case TaskStatus.RanToCompletion: 
        if (asyncTask.Result) 
         UpdateUI(uiScheduler, "OK"); 
        else 
        { 
         string strErrComplete = "Process failed."; 
         UpdateUI(uiScheduler, strErrComplete); 
        } 
        break; 
       case TaskStatus.Faulted: 
        string strFatalErr = String.Empty; 
        UpdateUI(uiScheduler, "Fatal Error); 
        if (task.Exception != null) 
         strFatalErr = task.Exception.InnerException.Message; 
        else 
         strFatalErr = "Operation failed"; 
        MessageBox.Show(strFatalErr); 
        break; 
      } 
      asyncTask.Dispose(); 
      return; 
     }, TaskScheduler.FromCurrentSynchronizationContext()); 
    } 
    catch (Exception eX) 
    { 
     Utils.ErrMsg(eX.Message); 
    } 
} 

我希望這有助於。

編輯。請注意，在上面的uiScheduler是UI線程的TaskScheduler。也就是說

TaskSheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext(); 

Answer 2

你爲什麼不只是提取方法？

private void SetLock(bool lock) 
    { 
     LoadButton.Enabled = !lock; 
     MonthEndDateEdit.Enabled = !lock; 
     BankIssuerListEdit.Enabled = !lock; 
     _updateMessageTaskInProgress = lock; 
    } 

    private void PerformUpdate() 
    { 
     if (!_updateMessageTaskInProgress) 
     { 
      SetLock(true); 
      Task updateMessages = Task.Factory.StartNew(() => 
      { 
       ExpensiveMethod(); 
      }); 

      // Task runs when updateMessages completes without exception. Runs on UI thread. 
      Task updateComplete = updateMessages.ContinueWith(update => 
      { 
       DoSuccessfulStuff(); 
       SetLock(false); 
      }, System.Threading.CancellationToken.None, TaskContinuationOptions.NotOnFaulted, TaskScheduler.FromCurrentSynchronizationContext()); 

      // Task runs when updateMessages completes with exception. Runs on UI thread. 
      Task updateFailed = updateMessages.ContinueWith(task => 
      { 
       DoFailureStuff(); 
       SetLock(false); 
      }, System.Threading.CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.FromCurrentSynchronizationContext()); 
     } 
    }