wpf-rule-mvvm-constraints

name	wpf-rule-mvvm-constraints
description	WPF MVVM layer-separation rules: no System.Windows in ViewModels, BCL-only types, CommunityToolkit.Mvvm base classes. Preloaded into MVVM-related wpf-dev-pack agents.
user-invocable	false

MVVM Constraints

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

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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.

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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

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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;

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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.

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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