NuExt.Minimal.Mvvm — nugetz

public class SearchViewModel : ViewModelBase
{
    public IAsyncCommand<string> SearchCommand { get; }
    public ICommand CancelCommand { get; }

    public SearchViewModel()
    {
        SearchCommand = new AsyncCommand<string>(SearchAsync, CanSearch)
        {
            AllowConcurrentExecution = true
        };

        CancelCommand = new RelayCommand(() => SearchCommand.Cancel());
    }

    private async Task SearchAsync(string query, CancellationToken cancellationToken)
    {
        await Task.Delay(1000, cancellationToken);
        Results = $"Results for: {query}";
    }

    private bool CanSearch(string query) => !string.IsNullOrWhiteSpace(query);

    private string _results = string.Empty;
    public string Results
    {
        get => _results;
        private set => SetProperty(ref _results, value);
    }
}

public class DataViewModel : ViewModelBase
{
    public IAsyncCommand LoadDataCommand { get; }

    public DataViewModel()
    {
        LoadDataCommand = new AsyncCommand(LoadDataAsync);

        LoadDataCommand.UnhandledException += (sender, e) =>
        {
            if (e.Exception is HttpRequestException httpEx)
            {
                ShowError($"Network error: {httpEx.Message}");
                e.Handled = true; // local tier handled
            }
        };
    }

    private async Task LoadDataAsync(CancellationToken cancellationToken)
    {
        throw new HttpRequestException("Connection failed");
    }

    private void ShowError(string message) { /* UI */ }
}

AsyncCommand.GlobalUnhandledException += (sender, e) =>
{
    Logger.LogError(e.Exception, "Global command error");
    e.Handled = true;
};

using Minimal.Mvvm;

public partial class ProductViewModel : ViewModelBase
{
    [Notify]
    private string _name = string.Empty;

    [Notify(Setter = AccessModifier.Private)]
    private decimal _price;

    public ProductViewModel()
    {
        SaveCommand = new AsyncCommand(SaveAsync);
    }

    [Notify]
    private async Task SaveAsync(CancellationToken token)
    {
        await Task.Delay(500, token);
        Price = 99.99m;
    }
}

public sealed class MyViewModel : ViewModelBase
{
    public MyViewModel(IServiceContainer fallback) : base(fallback)
    {
        // Application scope (global): ServiceProvider.Default for app-level services.
        ServiceProvider.Default.RegisterService<IMyService, MyService>();
        // ViewModel scope (local container); override per-VM if needed.
        Services.RegisterService<IMyService, MyVmSpecificService>();  // singleton
        Services.RegisterTransient<INotification>(() => new Toast()); // transient
    }

    public void Use()
    {
        // Resolution order: local → fallback → parent → default
        var svc = Services.GetService<IMyService>();
        var toast = Services.GetService<INotification>();
    }
}

public sealed class ValidateViewModel : ViewModelBase
{
    public IAsyncCommand ValidateCommand { get; }

    public ValidateViewModel()
    {
        // Often completes synchronously; ValueTask avoids allocations in that case.
        ValidateCommand = new AsyncValueCommand(ValidateAsync);
    }

    private ValueTask ValidateAsync(CancellationToken ct)
    {
        // synchronous fast path
        if (IsValidFast()) return ValueTask.CompletedTask;

        // fallback async path
        return SlowValidateAsync(ct);
    }

    private bool IsValidFast() => /* lightweight checks */;
    private async ValueTask SlowValidateAsync(CancellationToken ct)
    {
        await Task.Delay(50, ct);
        // heavy checks...
    }
}

using Minimal.Mvvm;
using System.Threading;
using System.Threading.Tasks;

public partial class LoginViewModel : ViewModelBase
{
    [Notify] private string _userName = string.Empty;
    [Notify] private string _password = string.Empty;

    // Field-based pattern: generator creates the LoginCommand property.
    // [UseCommandManager] auto-subscribes the property setter to WPF CommandManager.RequerySuggested.
    [Notify, UseCommandManager]
    private IAsyncCommand? _loginCommand;

    public LoginViewModel()
    {
        LoginCommand = new AsyncCommand(LoginAsync, CanLogin);
    }

    private bool CanLogin() =>
        !string.IsNullOrWhiteSpace(UserName) &&
        !string.IsNullOrWhiteSpace(Password);

    private async Task LoginAsync(CancellationToken ct)
    {
        await Task.Delay(250, ct);
        // sign-in...
    }
}

<Window x:Class="MyApp.Views.LoginView"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:MyApp.ViewModels"
        Title="Login" Width="360" Height="220">
    <Window.DataContext>
        <vm:LoginViewModel/>
    </Window.DataContext>

    <StackPanel Margin="16" VerticalAlignment="Center">
        <TextBox Margin="0,0,0,8"
                 Text="{Binding UserName, UpdateSourceTrigger=PropertyChanged}"/>
        <TextBox Margin="0,0,0,12"
                 Text="{Binding Password, UpdateSourceTrigger=PropertyChanged}"/>

        <!-- CanExecute will re-evaluate automatically on UI changes thanks to [UseCommandManager] -->
        <Button Content="Sign in"
                Command="{Binding LoginCommand}"
                HorizontalAlignment="Right"
                MinWidth="96" Padding="12,6"/>
    </StackPanel>
</Window>

Recommended: install the binary add‑on
```
dotnet add package NuExt.Minimal.Mvvm.Legacy
```
This adds AsyncValueCommand* for net462/netstandard2.0 and pulls System.Threading.Tasks.Extensions only on legacy.
Sources‑only workflow: opt‑in via .Sources and NUEXT_ENABLE_VALUETASK + System.Threading.Tasks.Extensions.

dotnet add package NuExt.Minimal.Mvvm

dotnet add package NuExt.Minimal.Mvvm.Sources