avalonia-mvvm

Avalonia MVVM

Overview

MVVM: Model (data/business), View (.axaml), ViewModel (presentation logic, bindable state). ViewModel knows nothing about View. Views bind to ViewModel properties and commands.

INotifyPropertyChanged (Manual)

public class PersonViewModel : INotifyPropertyChanged
{
    private string _name = "";
    public string Name
    {
        get => _name;
        set { _name = value; PropertyChanged?.Invoke(this, new(nameof(Name))); }
    }
    public event PropertyChangedEventHandler? PropertyChanged;
}

CommunityToolkit.Mvvm (Recommended)

Source-generator based, no reflection, clean code.

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

public partial class MainViewModel : ObservableObject
{
    [ObservableProperty]
    private string _name = "";

    [ObservableProperty]
    [NotifyCanExecuteChangedFor(nameof(SaveCommand))]
    private bool _isDirty;

    [RelayCommand(CanExecute = nameof(CanSave))]
    private async Task SaveAsync()
    {
        // save logic
    }

    private bool CanSave() => IsDirty && !string.IsNullOrEmpty(Name);
}

NuGet: CommunityToolkit.Mvvm

Generated: Name property with change notification, NameChanged partial method hook, SaveCommand as AsyncRelayCommand.

ReactiveUI (Alternative)

using ReactiveUI;

public class MainViewModel : ReactiveObject
{
    private string _name = "";
    public string Name
    {
        get => _name;
        set => this.RaiseAndSetIfChanged(ref _name, value);
    }

    public ReactiveCommand<Unit, Unit> SaveCommand { get; }

    public MainViewModel()
    {
        var canSave = this.WhenAnyValue(x => x.Name, n => !string.IsNullOrEmpty(n));
        SaveCommand = ReactiveCommand.CreateFromTask(SaveAsync, canSave);
    }

    private async Task SaveAsync() { /* ... */ }
}

	Avalonia 12.x (12.0+)	Avalonia 11.x (11.x)
NuGet	ReactiveUI.Avalonia (12.1.x on NuGet requires Avalonia >= 12.1.3; later 14.x line exists — check NuGet)	Avalonia.ReactiveUI (ends at 11.3.x)
Namespace	using ReactiveUI.Avalonia;	using Avalonia.ReactiveUI;