wpf-rule-prohibitions

Prohibitions

Items explicitly banned from wpf-dev-pack. Do NOT introduce any of these during code generation, review, or refactoring.

For terminology used below (View First / ViewModel First Composition, Stateful / Stateless ViewModel), see docs/TERMINOLOGY.md.

Adopted combinations (per chosen MVVM framework):

• CommunityToolkit.Mvvm path — ViewModel First Composition + Stateful ViewModel (Mappings.xaml + implicit DataTemplate)
• Prism 9 path — View First Composition + Stateful ViewModel (RegisterForNavigation + IRegionManager.RequestNavigate)

---

P-001: Mixing alternate composition mechanisms in the same project

P-001-a: Prism ViewModelLocator.AutoWireViewModel is prohibited

Prohibited:

<Window prism:ViewModelLocator.AutoWireViewModel="True" />

Classification: View First Composition (an alternate mechanism inside Prism)

Reason: The Prism path's single matching mechanism is RegisterForNavigation + IRegionManager.RequestNavigate. ViewModelLocator locates and attaches the ViewModel by naming convention after the View is instantiated; using both mechanisms in the same Prism project produces two parallel matching paths, increasing maintenance and cognitive cost.

P-001-b: DataContext = new XxxViewModel() in View code-behind is prohibited

Prohibited:

public XxxView()
{
    InitializeComponent();
    DataContext = new XxxViewModel();   // Prohibited
}

Classification: View First Composition (imperative variant)

Reason: In the CommunityToolkit.Mvvm path the single matching mechanism is Mappings.xaml + implicit DataTemplate (ViewModel First). A View directly choosing its own VM breaks that single-path policy. In the Prism path the single mechanism is RegisterForNavigation; manual DataContext assignment likewise breaks single-path.

P-001-c: Inline XAML DataContext declaration is prohibited

Prohibited:

<UserControl.DataContext>
    <vm:XxxViewModel />   <!-- Prohibited -->
</UserControl.DataContext>