WPF - How to display the cutom exception from view insted of viewmodel

Question

I have a WPF MMVM application and we are getting xml parser exception from viewmodel method. But the problem is I don't want to show the exception from viewmodel. I would like to show the message from view ( CustomMessageBox.Show() call from view)

As per the below code, I am calling CustomMessageBox.Show() from view model catch block. How can I call CustomMessageBox.Show() from xaml.cs or xaml ?

How can we notify the view about this and call CustomMessageBox.Showfrom view?. This code snippet is called in a WPF command.

Current implementation:

try
{
  var xamlReader = XamlReader.Parse(xamlText);
  var gb = modelTemplate.GetGraphicalObject("Icons");
  var strings = new Dictionary<string, string> { { "Default", xamlText } };
  gb.UpdateGraphicalObject(strings, null, null);
  if (xamlReader != null)
  {
    var view = new Viewbox();
    view.Child = (UIElement)xamlReader;
    view.Stretch = Stretch.Uniform;
    modelVM.Icon = view;
    }
  }
  catch (XamlParseException)
  {
    CustomMessageBox.Show("Invalid XAML file specified.", Properties.Resources.NextGenSim, MessageBoxButton.OK, MessageBoxImage.Error);
    //throw new XamlParseException("Invalid XAML file specified");
  }

Answer 1

If you're using a messenger / event aggregator (eg MVVM Light), you can send a message containing the exceptions details from the viewmodel to the view, which, when received, can trigger the message box to show.

Using MVVM Light , it might look like the following:

Viewmodel:

Messenger.Default.Send(new ErrorMessage("Invalid XAML file specified.",
                       Properties.Resources.NextGenSim));

View

Messenger.Default.Register<ErrorMessage>(this, message =>
    {
        CustomMessageBox.Show(message.Message, message.Details, 
                              MessageBoxButton.OK, MessageBoxImage.Error);
    }

The ErrorMessage is a custom class, containing whatever details about the exception you need to display to the user.

Answer 2

您可以使用ValueConverter创建一个具有可视性绑定到ViewModel属性ErrorMessage的模式Popup ValueConverter ，当给定的源不为null或为空时，该方法将返回true。