WPF - MVVM Command binding on Sub ViewModel

Question

Hi,

I've got a VehicleViewModel that has a sub ViewModel of NotesViewModel

public IManageVehicleNotesViewModel NotesViewModel { get; set; }

On the first activation of VehicleViewModel I activate the sub ViewModel.

NotesViewModel.Activate();

The activation calls a method to init a number of Commands, I've break pointed this and its being called.

CreateCommand = new DelegateCommand<object>(OnCreateCommand, CanCreate);

However although the TextBoxes are binding on the sub View (so the DataContext is in place) none of the commands are binding - I've tried to calling RaiseCanExecuteChanged on the commands but they don't disable, enable or call the methods as expected.

I don't know whether its relevant (as the TextBoxes are binding) but I'm associating the View and ViewModel using a ResourceDictionary as so ...

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:v="clr-namespace:GTS.GRS.N3.Modules.Vehicles.Views"
    xmlns:vm="clr-namespace:GTS.GRS.N3.Modules.Vehicles.Model">
  <DataTemplate DataType="{x:Type vm:ManageVehicleViewModel}">
    <v:ManageVehicleView />
  </DataTemplate>
  <DataTemplate DataType="{x:Type vm:ManageVehicleNotesViewModel}">
    <v:ManageVehicleNotesView />
  </DataTemplate>
</ResourceDictionary>

The commands on the top level VehicleViewModel work.

Has anyone experienced anything like this? Is it the order I'm doing things? Any help gratefully received!

Cheers,

Andy

Answer 1

Do this and check the output to see what is going on:

<UserControl …
     xmlns:diagnostics="clr-namespace:System.Diagnostics;assembly=WindowsBase" />

<Button Command="{Binding MyCommand, 
                  diagnostics:PresentationTraceSources.TraceLevel=High}" … />

It should report what object it's actually trying to bind to, etc. Check your output window while you are running to see what is going on with that binding.

Answer 2

Does the CreateCommand property trigger the PropertyChanged event ? If it doesn't, the UI won't be notified when you assign it...

Try to use a tool like Snoop to check whether the Command property of the button is set