.NET/C# WPF With Catel MVVM Best Practices

C# WPF coding guidelines and best practices. MUST follow these rules. Use when reviewing/writing C# WPF code.

ViewModel Definition and Registration

• Base Class: Always inherit from Catel.MVVM.ViewModelBase.
• Services: Inject services (e.g., IUIVisualizerService, IMessageService, INavigationService) via the constructor. Do not use global state.
• Constructor Injection: ViewModels should not use the service locator pattern. Enforce constructor injection for all services.
• Initialization: Place time-consuming asynchronous initialization logic inside the InitializeAsync() override, rather than inside the constructor.
• Saving/Canceling: Override SaveAsync() and CancelAsync() to manage data persistence and dialog results correctly.

Properties Model vs ViewModel

• Dependency Properties: Wrap bound properties using Catel.MVVM.ViewModelToModelAttribute when mirroring a domain model.
• Field-based Properties: Use Catel's RegisterProperty or AdvancedPropertyChanged instead of standard INotifyPropertyChanged boilerplate.
• Validation: Implement ValidateFields and ValidateBusinessRules overrides to encapsulate data integrity rules at the ViewModel level rather than pushing logic to the code-behind.

Commands & Interactivity

• Command Binding: Use Catel.MVVM.Command or Catel.MVVM.TaskCommand for asynchronous operations.
• CanExecute: Always define corresponding Can[Action] methods (returning bool) for every [Action]Command to automatically handle UI button states.
• Code-Behind Restriction: Do not write UI event handlers in .xaml.cs files unless strictly necessary. Use Catel's command bindings or attached behaviors for WPF UI interactions.

Views and Data Binding

• Base Class: Ensure views inherit from Catel.Windows.Controls.Window or Catel.Windows.Controls.UserControl.
• View-to-ViewModel Mapping: Rely on Catel's automatic view model locator rather than explicitly setting DataContext in code.
• Compiled Bindings: Wherever possible in Catel Views, use {Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type catel:UserControl}}, Path=ViewModel.PropertyName} to ensure binding safety.

Messaging and Orchestration

• Messenger: Use Catel.Messaging.IMessageMediator for cross-ViewModel communication instead of tight coupling.
• Life-cycle Registration: Ensure message subscriptions are safely registered and deregistered to prevent memory leaks in WPF.