Introduction
WPF and the MVVM (Model-View-ViewModel) pattern are powerful tools for desktop development. However, as applications grow, the technical plumbing—commands, data binding, notifications—can sometimes cloud the architectural intent. We can easily lose track of the conceptual meaning of our classes behind their technical implementations.
To bring more clarity to my desktop architectures, let's try a lightweight framework Clprolf. The goal is simple: use basic custom C# attributes to give every class a clear, human-readable role, and enforce these boundaries with automated architecture tests using ArchUnitNET.
Here is how it looks in practice.
The Core Concepts: Agents and Workers
Instead of categorizing code strictly by technical layers, Clprolf looks at the application as a team of actors working together:
Agents: Core components that carry an identity, state, representation, or behavioral intention.
Workers: Quiet executors or infrastructure tools that handle background or mechanical tasks.
When applied to WPF and MVVM, the system naturally organizes into three distinct types of Agents:
Domain Agents (User): The pure business entities holding the core data and identity.
Presentation Agents (UserViewModel): The ambassadors between the user and the system, orchestrating data and validating user intentions.
System-Oriented Agents (UserWindow&RelayCommand): Noble UI components whose purpose is to interact with and feed the hidden, native rendering engine of the .NET framework.
The Code in Action
Here is a streamlined look at how a standard CRUD ViewModel expresses its semantic role through attributes and clean design:
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows.Input;
using Clprolf.ArchUnitNet.Attributes;
namespace Clprolf.Example.WPF.Mvvm.Impl
{
[ClAgent] // Marked as a Presentation Agent
public class UserViewModel : IUserViewModel
{
public event PropertyChangedEventHandler? PropertyChanged;
// ObservableCollection handles UI notification for list updates
public ObservableCollection<User> Users { get; set; } = new();
private User? _selectedUser;
public User? SelectedUser
{
get => _selectedUser;
set
{
if (_selectedUser != value)
{
_selectedUser = value;
OnPropertyChanged(nameof(SelectedUser));
if (_selectedUser != null) NewUserName = _selectedUser.Name;
}
}
}
private string _newUserName = string.Empty;
public string NewUserName
{
get => _newUserName;
set
{
if (_newUserName != value)
{
_newUserName = value;
OnPropertyChanged(nameof(NewUserName));
}
}
}
// Intention Agents (CRUD Commands)
public ICommand AddCommand { get; }
public UserViewModel()
{
AddCommand = new RelayCommand(ExecuteAdd, CanExecuteAdd);
// Initial data seeding
// (In a full production setup, this would be fetched from a Repository Worker)
Users.Add(new User("Alice"));
Users.Add(new User("Bob"));
}
public void ExecuteAdd(object? parameter)
{
Users.Add(new User(NewUserName));
NewUserName = string.Empty;
// Save to repository worker here...
}
public bool CanExecuteAdd(object? parameter) => !string.IsNullOrWhiteSpace(NewUserName);
private void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
}
The Architecture Blueprint
To see how this language structures a real application, here is the exact layout of the WPF project. Notice how the namespaces map directly to our semantic roles rather than generic UI folders:
Clprolf.Example.WPF/
│
├── App.xaml.cs --> [ClWorker] (Application Bootstrapper)
│
├── Entities/
│ └── User.cs --> [ClAgent] (Domain Identity)
│
├── Mvvm/
│ ├── IUserViewModel.cs --> [ClFamily] [ClAgent] (Contract)
│ └── Impl/
│ └── UserViewModel.cs --> [ClAgent] (Presentation Ambassador)
│
└── Agents/
└── Impl/
└── SystemOriented/
├── UserWindow.xaml.cs --> [ClAgent] (UI Component)
├── RelayCommand.cs --> [ClAgent] (Intention Driver)
└── IClNotifyPropertyChanged.cs --> [ClTrait] (Structural Behavior)
As you can see, every single component—from the window to the command framework—has been assigned a strict semantic responsibility.
Wiring the Ecosystem Together
To understand how these Agents interact, look at how the application starts.
First, we have our UserWindow, a System-Oriented Agent designed to serve the native WPF rendering engine by hosting the visual tree and binding the context:
[ClAgent]
public partial class UserWindow : Window
{
public UserWindow(UserViewModel vm)
{
InitializeComponent();
DataContext = vm;
}
}
Then, we have the App.xaml.cs. This is not an Agent; it has no business intent. It is a Clprolf Worker—an automated executor whose only job is to assemble the pieces, inject the dependencies, and start the factory:
[ClWorker]
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
var vm = new UserViewModel();
var userWin = new UserWindow(vm);
userWin.Show(); // The worker hands over control to the System Agents
}
}
Guarding the Architecture with ArchUnitNET
To ensure these semantic boundaries are never violated during development, we use automated architecture tests. For instance, we can write a rule ensuring that any interface marked as a Trait (a reusable structural behavior) only extends other Traits or external system interfaces, preventing illegal coupling with hard Agents.
Here is the condition that enforces this:
internal sealed class TraitInterfacesMustExtendOnlyTraitInterfacesCondition : ICondition<Interface>
{
public string Description => "extend only trait interfaces";
public IEnumerable<ConditionResult> Check(IEnumerable<Interface> objects, Architecture architecture)
{
foreach (var interf in objects)
{
if (!interf.IsTrait()) continue;
// Validate that Clprolf parents are strictly other Traits
bool allParentsAreTraitsOrNonClprolf = interf.ImplementedInterfaces.All(parent =>
!parent.IsClprolf() || parent.IsTrait()
);
yield return new ConditionResult(
interf,
allParentsAreTraitsOrNonClprolf,
"Verifying semantic inheritance rules.");
}
}
}
Conclusion
By mapping the technical structure of MVVM into a simple, unified vocabulary of Agents and Workers, the cognitive load drops. The architecture stops being just about "WPF mechanics" and becomes a clear map of responsibilities.
The main benefit of this approach is consistency: whether you are looking at a desktop view-model, a web API controller, or a console application, the semantic definitions remain the same.
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