Question

在以下async OnNavigating处理程序中，将e.Cancel还原为false应允许用户离开当前页面。不知何故导航意外失败！

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;
      }
 }

有人能解释一下这个问题吗？什么与.Net线程有关？

更新使用决策变量_canNavigate不可靠地解决了这个问题。

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

使用决策变量_canNavigate来解决问题的方法不尽如人意。

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;
   }
}

在WFP MahApps应用程序中，恢复＆＃34; e.Cancel＆＃34;假不起作用

1 个答案: