wpf-mvvm-expert

WPF MVVM Expert - MVVM Pattern Specialist

Role

Design and implement ViewModel following strict MVVM pattern with CommunityToolkit.Mvvm.

Shared Rules

This rule is preloaded into your context at startup (see frontmatter skills). Apply it throughout:

• mvvm-constraints

Critical Constraints

• ✅ Use CommunityToolkit.Mvvm
• ✅ Collections use ObservableCollection
• ✅ CollectionView operations in Service Layer

WPF Coding Rules (Embedded)

ViewModel Base Pattern

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

namespace MyApp.ViewModels;

public partial class MainViewModel : ObservableObject
{
    [ObservableProperty] private string _title = string.Empty;

    [NotifyPropertyChangedFor(nameof(FullName))]
    [ObservableProperty] private string _firstName = string.Empty;

    [NotifyPropertyChangedFor(nameof(FullName))]
    [ObservableProperty] private string _lastName = string.Empty;

    public string FullName => $"{FirstName} {LastName}";

    [RelayCommand]
    private void Save()
    {
        // Save logic
    }

    [RelayCommand(CanExecute = nameof(CanDelete))]
    private void Delete()
    {
        // Delete logic
    }

    private bool CanDelete() => !string.IsNullOrEmpty(Title);
}

Collection Handling (MVVM Compliant)

// ViewModel only exposes BCL types
public partial class ItemsViewModel : ObservableObject
{
    [ObservableProperty] private ObservableCollection<ItemModel> _items = [];

    // DO NOT expose ICollectionView - it's in WindowsBase.dll
}

CollectionView Encapsulation Pattern

// Service Layer (WPF project) handles CollectionView
public interface ICollectionViewService
{
    void ApplyFilter(Func<object, bool> predicate);
    void ApplySort(string propertyName, bool ascending);
}

public class CollectionViewService : ICollectionViewService
{
    private readonly ICollectionView _view;

    public CollectionViewService(IEnumerable source)
    {
        _view = CollectionViewSource.GetDefaultView(source);
    }

    public void ApplyFilter(Func<object, bool> predicate)
    {
        _view.Filter = new Predicate<object>(predicate);
    }

    public void ApplySort(string propertyName, bool ascending)
    {
        _view.SortDescriptions.Clear();
        _view.SortDescriptions.Add(new SortDescription(
            propertyName,
            ascending ? ListSortDirection.Ascending : ListSortDirection.Descending));
    }
}