Question

我正在努力掌握async / await和TPL，所以我正在尝试一些事情。我看到有很多类似的问题，但我仍然无法弄清楚这里发生了什么。如果我遗漏了一些明显或已经回答的问题，请道歉。

如果您不喜欢vb.net请convert it;）

为什么还会出现CurrentDomain.UnhandledException？我认为当我访问task.Exception并在句柄中返回true时会观察到它，因为它被观察到它不会自动传播？

      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

在现代代码中，您应该使用await而不是ContinueWith。它比乱搞任务调度程序，聚合异常等等更容易：

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");
}

任务ContinueWith OnlyOnFaulted仍然获取CurrentDomain.UnhandledException

1 个答案: