Manage complex UI with MVVM

Question

Hi

My question is actually about starting an application with MVVM :

My main screen will host many screens. I understand that they will be UserControls.

But i don't see where i instantiate then when i want, when i show them and when i hide them ?

The logic is not clear to me. Can someone explain me or point me to a simple and clear example ?

Thanks John

Answer 1

Josh Smith's article in MSDN magazine is probably the best place to get started.

Answer 2

You could use an existing application framework to help manage this rather than doing it yourself. Caliburn in particular addresses this problem with its IPresenter Component Model. I'm sure there are others out there too.

Answer 3

Imagine that you have got a MainViewModel which binds to the main screen.Let the MainViewModel be a singleton class and it has a 'CurrentViewModel' property (INotifypropertyChanged implemented) in it. Now you can instantiate any particular ViewModel (based on a Command/Click) and assign the instance as below

MainViewModel.Instance.CurrentViewModel = new SomeViewModel();

So now your main screen XAML will have

  <Window> 
     <ContentControl Content="{Binding CurrentViewModel,Source={x:static vm:MainViewModel.Instance}}"
 </Window>

You need to define proper DataTemplates for each ViewModels (View to ViewModel Mapping). That will look like

<DataTemplate DataType="{x:Type vm:SomeViewModel}">
     <view:SomeView/>
</DataTemplate>

Here SomeView is the UserControl corresponds to the SomeVieModel.

Hope this explains the MVVM architecture very briefly