how to avoid ViewModelViewHost fallingl back to Locate View without constract

[newbienewbie]

Senario

I have multiple different views that share the same ViewModel.

class ViewA : UserControl, IViewFor<WaitingFunVM>
{
}

class ViewB: UserControl, IViewFor<WaitingFunVM>
{
}

Locator.CurrentMutable.Register( typeof(ViewA), typeof<IVewFor<WaitingFunVM>>,  ConstractA);
Locator.CurrentMutable.Register( typeof(ViewB), typeof<IVewFor<WaitingFunVM>>,  ConstractB);

I only defined the ViewModel (e.g. WaitingFunVM) and let those views defined by other developers. The other developers provide user-defined views in plugins. And finally I locate the related views by a contract:

<rxui:ViewModelViewHost x:Name="myview"  ViewContract="ConstractB" />

Normally, it will render the ViewB without any problem.

However, in some case, the ViewB implementation is optional: Plugins author might not implement the ViewB at all.

What I want is that it should show nothing instead of rending ViewA if a specify ViewContract="ConstractB".

The Current Implementation

The current implementation of ViewModelViewHost resolves the View in the following way:

  private void ResolveViewForViewModel(object? viewModel, string? contract)
  {
        // ...
        var viewInstance = viewLocator.ResolveView(viewModel, contract) ?? viewLocator.ResolveView(viewModel);

It means the current implementation falls back to resolve view with no contract if nothing found.

If the ResolveViewForViewModel() must not be protect virtual, is it possible add a property so that we can bypass the fallback to viewLocator.ResolveView(viewModel);?

e.g. :

var viewInstance = viewLocator.ResolveView(viewModel, contract) ;
if(viewInstance == null && !this.ContractFallbackByPass) 
{
    viewInstance = viewLocator.ResolveView(viewModel);
}

[glennawatson]

Adding a property is definitely a possibility as long as it defaults to the current fallback technique so not to break existing users that rely on it.