WPF MVVM with CommunityToolkit.Mvvm

Description

Build and review WPF applications with MVVM using CommunityToolkit.Mvvm - source-generated observable properties, RelayCommand and AsyncRelayCommand with CanExecute and NotifyCanExecuteChangedFor, XAML data binding (modes, UpdateSourceTrigger, StringFormat, DataContext), ObservableCollection and collection views for filtering and sorting, validation with ObservableValidator and data annotations, DataTemplate-based navigation from a shell ViewModel, WeakReferenceMessenger between ViewModels, and Microsoft.Extensions.DependencyInjection wiring in App.xaml.cs - keeping ViewModels free of WPF types so they unit-test. Use whenever the project is WPF (.xaml, UseWPF), references CommunityToolkit.Mvvm, the user writes ViewModels, commands or bindings, a button stays disabled or enabled wrongly, the UI doesn't update, a list doesn't refresh, or asks how to structure or navigate a WPF app.