MVVM Constraints

Rules for enforcing strict MVVM layer separation in wpf-dev-pack projects.

Prohibited DLL References in ViewModel Projects

ViewModel projects must NOT reference these assemblies:

• WindowsBase.dll
• PresentationFramework.dll
• PresentationCore.dll

If any of these appear in a .csproj targeting the ViewModel layer, remove them immediately.

Prohibited Using Statements

The following namespaces must never appear in ViewModel code:

// Prohibited in ViewModel projects
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Media;
using System.Windows.Input;   // except ICommand — use CommunityToolkit.Mvvm instead

Allowed Using Statements

These namespaces are safe for ViewModels:

// Allowed
using System.Collections.ObjectModel;
using System.Collections.Generic;
using System.ComponentModel;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

ViewModel Type Restrictions

ViewModel properties and constructor parameters must use BCL types only:

• string, int, double, bool, decimal, DateTime, Guid
• ObservableCollection<T>, List<T>, IEnumerable<T>
• Other ViewModels or domain model types

Do NOT expose WPF types (Brush, Visibility, ImageSource, Thickness, etc.) as ViewModel properties. Convert in the View layer using converters or triggers.

CommunityToolkit.Mvvm

Prefer CommunityToolkit.Mvvm for all ViewModel base classes and commands:

• Inherit from ObservableObject or ObservableRecipient
• Use [ObservableProperty] for bindable properties (source-generated)
• Use [RelayCommand] for commands (source-generated)
• Never hand-roll INotifyPropertyChanged or ICommand implementations