davidortinau/maui-skills/maui-dependency-injection

// ❌ ViewModel registered as Singleton — stale data across navigations
builder.Services.AddSingleton<DetailViewModel>();
 
// ✅ ViewModels are Transient — fresh instance each navigation
builder.Services.AddTransient<DetailViewModel>();

// ❌ Resolving services during XAML parse — container may not be ready
public App(IDataService data)
{
    InitializeComponent(); // XAML parses here
    _data = data;          // may fail for types not yet resolved
}
 
// ✅ Defer service resolution to CreateWindow
public partial class App : Application
{
    private readonly IServiceProvider _services;
 
    public App(IServiceProvider services)
    {
        _services = services;
        InitializeComponent();
    }
 
    protected override Window CreateWindow(IActivationState? activationState)
    {
        // Safe — container is fully built
        var mainPage = _services.GetRequiredService<MainPage>();
        return new Window(new AppShell());
    }
}

// ❌ Page not registered — constructor injection silently skipped
// builder.Services.AddTransient<DetailPage>(); // missing!
 
// ✅ Always register pages that need injection
builder.Services.AddTransient<DetailPage>();
builder.Services.AddTransient<DetailViewModel>();

// ❌ Service locator scattered through code — hard to test, hides dependencies
public void DoWork()
{
    var service = this.Handler.MauiContext.Services.GetService<IDataService>();
    service.Load();
}
 
// ✅ Constructor injection — explicit, testable
public class MyViewModel(IDataService dataService)
{
    public void DoWork() => dataService.Load();
}

// ❌ No registration on Windows — GetService returns null
#if ANDROID
builder.Services.AddSingleton<INotificationService, AndroidNotificationService>();
#elif IOS || MACCATALYST
builder.Services.AddSingleton<INotificationService, AppleNotificationService>();
#endif
 
// ✅ Cover all platforms or provide a no-op fallback
#if ANDROID
builder.Services.AddSingleton<INotificationService, AndroidNotificationService>();
#elif IOS || MACCATALYST
builder.Services.AddSingleton<INotificationService, AppleNotificationService>();
#elif WINDOWS
builder.Services.AddSingleton<INotificationService, WindowsNotificationService>();
#endif