MVVM

View ↔ ViewModel ↔ Model: the ViewModel exposes bindable state and commands.

Context

Apps with declarative binding (WPF, MAUI, Avalonia, Blazor).

Solution

The View binds to the ViewModel, which exposes observable properties and ICommands. The Model represents the domain.

public class OrderViewModel : INotifyPropertyChanged
{
    private string _customer = "";
    public string Customer { get => _customer; set { _customer = value; OnChange(); } }

    public ICommand SaveCommand { get; }
    public OrderViewModel(IOrderService svc) =>
        SaveCommand = new RelayCommand(async () => await svc.SaveAsync(new Order(Customer)));

    public event PropertyChangedEventHandler? PropertyChanged;
    private void OnChange([CallerMemberName] string? n = null) =>
        PropertyChanged?.Invoke(this, new(n));
}

Tradeoffs

Pro	Con
Clear separation of concerns	Notification boilerplate
Testable without bringing up UI	Bindings difficult to debug

#architecture #ui #wpf #maui