在 WFP MahApps 应用程序中，将"e.Cancel"恢复为 false 不起作用

Question

在下面的async onnavigationhandler中，将e.Cancel恢复为false应该允许用户从当前页面导航出去。不知怎的，导航意外地失败了!

private async void NavigationService_OnNavigating(object sender, NavigatingCancelEventArgs e)
 {
      var model = DataContext as ViewModel;
      if (model == null || !model.IsDirty) return;
      e.Cancel = true;
      var option = MessageDialogResult.Negative;
      try
      {
           var metroWindow = (MainWindow)Application.Current.MainWindow;
           option = await metroWindow.ShowMessageAsync("Form", "Quit?", MessageDialogStyle.AffirmativeAndNegative);
      }
      finally
      {
           if (option == MessageDialogResult.Affirmative)
           //******Allow the user to move away********
           e.Cancel = false;
      }
 }

有谁能解释一下这个问题吗?任何与。net线程相关的东西?

更新:用决策变量_canNavigate求解了该问题。

private bool _canNavigate = false;
private async void NavigationService_OnNavigating(object sender, NavigatingCancelEventArgs e)
{
    var model = DataContext as ViewModel;
    if (model == null || !model.IsDirty) return;
    if (!_canNavigate)
    {
        e.Cancel = true;
        var metroWindow = (MainWindow)Application.Current.MainWindow;
        var option = await metroWindow.ShowMessageAsync("Form", "Quit?", MessageDialogStyle.AffirmativeAndNegative);
        if (option == MessageDialogResult.Affirmative)
        {
            _canNavigate = true;
            _navigationService.Navigate(e.Uri);
        }
        else _canNavigate = false;
    }
    else
    {
         _canNavigate = false;
    }
}

Answer 1

这个问题已经用决策变量_canNavigate笨拙地解决了。

private bool _canNavigate = false;
private async void NavigationService_OnNavigating(object sender, NavigatingCancelEventArgs e)
{
   var model = DataContext as ViewModel;
   if (model == null || !model.IsDirty) return;
   if (!_canNavigate)
   {
       e.Cancel = true;
       var metroWindow = (MainWindow)Application.Current.MainWindow;
       var option = await metroWindow.ShowMessageAsync("Form", "Quit?", MessageDialogStyle.AffirmativeAndNegative);
       if (option == MessageDialogResult.Affirmative)
       {
           _canNavigate = true;
           _navigationService.Navigate(e.Uri);
       }
       else _canNavigate = false;
   }
   else
   {
        _canNavigate = false;
   }
}