MyApp/
├── MyApp/                    # Shared code
│   ├── App.xaml              # Application entry
│   ├── MauiProgram.cs        # DI and configuration
│   ├── Views/                # XAML pages
│   ├── ViewModels/           # MVVM ViewModels
│   ├── Models/               # Domain models
│   ├── Services/             # Business logic
│   └── Platforms/            # Platform-specific code
│       ├── Android/
│       ├── iOS/
│       ├── MacCatalyst/
│       └── Windows/
└── MyApp.Tests/

public partial class ProductsViewModel(IProductService productService) : ObservableObject
{
    [ObservableProperty]
    private ObservableCollection<Product> _products = [];

    [ObservableProperty]
    [NotifyCanExecuteChangedFor(nameof(LoadProductsCommand))]
    private bool _isLoading;

    [RelayCommand(CanExecute = nameof(CanLoadProducts))]
    private async Task LoadProductsAsync()
    {
        IsLoading = true;
        try
        {
            var items = await productService.GetAllAsync();
            Products = new ObservableCollection<Product>(items);
        }
        finally
        {
            IsLoading = false;
        }
    }

    private bool CanLoadProducts() => !IsLoading;
}

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:vm="clr-namespace:MyApp.ViewModels"
             x:Class="MyApp.Views.ProductsPage"
             x:DataType="vm:ProductsViewModel">

    <RefreshView Command="{Binding LoadProductsCommand}"
                 IsRefreshing="{Binding IsLoading}">
        <CollectionView ItemsSource="{Binding Products}">
            <CollectionView.ItemTemplate>
                <DataTemplate x:DataType="models:Product">
                    <VerticalStackLayout Padding="10">
                        <Label Text="{Binding Name}" FontSize="18" />
                        <Label Text="{Binding Price, StringFormat='{0:C}'}" />
                    </VerticalStackLayout>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
    </RefreshView>
</ContentPage>

public static class MauiProgram
{
    public static MauiApp CreateMauiApp()
    {
        var builder = MauiApp.CreateBuilder();
        builder
            .UseMauiApp<App>()
            .ConfigureFonts(fonts =>
            {
                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
            });

        // Services
        builder.Services.AddSingleton<IProductService, ProductService>();
        builder.Services.AddSingleton<INavigationService, NavigationService>();

        // ViewModels
        builder.Services.AddTransient<ProductsViewModel>();
        builder.Services.AddTransient<ProductDetailViewModel>();

        // Pages
        builder.Services.AddTransient<ProductsPage>();
        builder.Services.AddTransient<ProductDetailPage>();

        return builder.Build();
    }
}

// Register routes
Routing.RegisterRoute(nameof(ProductDetailPage), typeof(ProductDetailPage));

// Navigate with parameters
await Shell.Current.GoToAsync($"{nameof(ProductDetailPage)}?id={product.Id}");

// Receive parameters
[QueryProperty(nameof(ProductId), "id")]
public partial class ProductDetailViewModel : ObservableObject
{
    [ObservableProperty]
    private string _productId;

    partial void OnProductIdChanged(string value)
    {
        LoadProduct(value);
    }
}

public interface INavigationService
{
    Task NavigateToAsync<TViewModel>(object? parameter = null);
    Task GoBackAsync();
}

public class NavigationService : INavigationService
{
    public async Task NavigateToAsync<TViewModel>(object? parameter = null)
    {
        var route = typeof(TViewModel).Name.Replace("ViewModel", "Page");
        var query = parameter is null ? "" : $"?id={parameter}";
        await Shell.Current.GoToAsync($"{route}{query}");
    }

    public Task GoBackAsync() => Shell.Current.GoToAsync("..");
}

// Services/DeviceService.cs (shared)
public partial class DeviceService
{
    public partial string GetDeviceId();
}

// Platforms/Android/DeviceService.cs
public partial class DeviceService
{
    public partial string GetDeviceId()
    {
        return Android.Provider.Settings.Secure.GetString(
            Android.App.Application.Context.ContentResolver,
            Android.Provider.Settings.Secure.AndroidId);
    }
}

// Platforms/iOS/DeviceService.cs
public partial class DeviceService
{
    public partial string GetDeviceId()
    {
        return UIKit.UIDevice.CurrentDevice.IdentifierForVendor?.ToString() ?? "";
    }
}

public string GetPlatformInfo()
{
#if ANDROID
    return $"Android {Android.OS.Build.VERSION.Release}";
#elif IOS
    return $"iOS {UIKit.UIDevice.CurrentDevice.SystemVersion}";
#elif MACCATALYST
    return "macOS Catalyst";
#elif WINDOWS
    return "Windows";
#else
    return "Unknown";
#endif
}

[Fact]
public async Task LoadProducts_UpdatesCollection()
{
    var mockService = new Mock<IProductService>();
    mockService.Setup(s => s.GetAllAsync())
        .ReturnsAsync(new[] { new Product { Name = "Test" } });

    var viewModel = new ProductsViewModel(mockService.Object);

    await viewModel.LoadProductsCommand.ExecuteAsync(null);

    Assert.Single(viewModel.Products);
    Assert.Equal("Test", viewModel.Products[0].Name);
}