Question

In my WPF (4.0) application I’m using Viewmodel-first pattern. Hence, my viewmodels are created first, then the views – using data templates. A working demo can be found here.

Now, from within the created views (code-behind), I need to modify a property of the viewmodel. In a View-first approach, I would simply access a named viewmodel instance. However, the Viewmodel-first approach does not allow for this. There is a viewmodel, but the view does not care what it is.

BAD:

Sure you can get hold of the DataContext and use it, but that effectively couples the view and t
the viewmodel.

private void MyView_Loaded(object sender, RoutedEventArgs e)
{
    this.viewModel = DataContext as MyViewModel;
}

There has to be a recommended pattern for this. Commands? Messages? Please help!

Q: How do I modify (set a property) the active viewmodel?

Answer 1

Use Bindings to pass data from View to ViewModel and commands to active the ViewModel.

Commands should use a binding to a execute a Command on the ViewModel.

Messages should be used to communicate between ViewModels.

.