任務ContinueWith OnlyOnFaulted仍然得到CurrentDomain.UnhandledException異常

Question

我想獲得異步/等待和TPL的堅實把握，所以我正在嘗試一些事情。我發現有很多類似的問題，但我仍然無法弄清楚這裏發生了什麼。道歉，如果我失去了一些明顯的或已經回答的問題。

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爲什麼CurrentDomain.UnhandledException仍時有發生？我認爲它會被觀察當我訪問task.Exception並在句柄中返回true，並且因爲它被觀察到它不會自動傳播？

 Public Function ContinueWith_ExceptionHandling_Flattening() As Threading.Tasks.Task(Of Integer) 
     Dim s As String = "ContinueWith_ExceptionHandling_Flattening" 
     Dim context = TaskScheduler.FromCurrentSynchronizationContext() 

     AddHandler AppDomain.CurrentDomain.UnhandledException, AddressOf CurrentDomain_UnhandledException 

     Dim t As Task(Of Integer) = Task.Run(Function() ThrowException(0, "")) 
     t.ContinueWith(Function(a) CreateAndShowResultForm(a.Result, s), Threading.CancellationToken.None, TaskContinuationOptions.NotOnFaulted, context) 'doesnt run if t faulted! 
     t.ContinueWith(AddressOf HandleTask_Exception, Threading.CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, context) 'only runs if t faulted 

     Return t 
    End Function 


    Private Sub HandleTask_Exception(x As task) 
     x.Exception.Flatten.Handle(Function(ex) 
             Select Case ex.GetType 
              Case GetType(NoNullAllowedException) 
               MessageBox.Show("NoNullAllowedException ...handled by HandleTask_Exception") 
              Case Else 
               MessageBox.Show(ex.Message & " ...handled by HandleTask_Exception") 
             End Select 
             Return True 
            End Function) 
    End Sub 

'THIS IS STILL BEING HIT (I am looking for explanation as to why) 
    Private Sub CurrentDomain_UnhandledException(sender As Object, e As UnhandledExceptionEventArgs) 
     MessageBox.Show("CurrentDomain_UnhandledException: " & CType(e.ExceptionObject, Exception).Message) 
    End Sub 



'Calling code 
Public Async Function ContinueWith_ExceptionHandling_Flattening_Helper() As Task(Of Integer) 
      Return Await cls.ContinueWith_ExceptionHandling_Flattening 
    End Function 

Answer 1

在現代的代碼，你應該使用await而不是ContinueWith。這是不是與任務調度，彙總例外，和諸如此類的東西上浪費得多：

public async Task<int> ContinueWith_ExceptionHandling_FlatteningAsync() 
{ 
    string s = "ContinueWith_ExceptionHandling_Flattening"; 

    AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException; 

    Task<int> t = Task.Run(() => ThrowException(0, "")); 
    try 
    { 
    var result = await t; 
    CreateAndShowResultForm(result, s); 
    return result; 
    } 
    catch (Exception ex) 
    { 
    HandleTask_Exception(ex); 
    throw; 
    } 
} 

private void HandleTask_Exception(Exception ex) 
{ 
    MessageBox.Show(ex.Message + " ...handled by HandleTask_Exception"); 
}