Dependency Injection in .NET MAUI

Service Registration in MauiProgram.cs

Register services on builder.Services inside CreateMauiApp():

public static MauiApp CreateMauiApp()
{
    var builder = MauiApp.CreateBuilder();
    builder.UseMauiApp<App>();

    // Services
    builder.Services.AddSingleton<IDataService, DataService>();
    builder.Services.AddTransient<IApiClient, ApiClient>();

    // ViewModels
    builder.Services.AddTransient<MainViewModel>();
    builder.Services.AddTransient<DetailViewModel>();

    // Pages
    builder.Services.AddTransient<MainPage>();
    builder.Services.AddTransient<DetailPage>();

    return builder.Build();
}

Lifetime Guidance

Rule of thumb: Use AddTransient for ViewModels and Pages. Use AddSingleton for services that hold shared state or are expensive to construct. Avoid AddScoped unless you create and manage IServiceScope instances yourself.

Constructor Injection (Preferred)

Inject dependencies through the constructor. The DI container resolves them automatically when the type is itself resolved from the container:

public class MainViewModel
{
    private readonly IDataService _dataService;
    private readonly IApiClient _apiClient;

    public MainViewModel(IDataService dataService, IApiClient apiClient)
    {
        _dataService = dataService;
        _apiClient = apiClient;
    }
}

ViewModel → Page Pattern

Register both the ViewModel and the Page. Inject the ViewModel into the Page constructor and assign it as BindingContext:

public partial class MainPage : ContentPage
{
    public MainPage(MainViewModel viewModel)
    {
        InitializeComponent();
        BindingContext = viewModel;
    }
}

Automatic Resolution via Shell Navigation

When Pages are registered in the DI container and registered as Shell routes, Shell resolves them (and their dependencies) automatically:

// In MauiProgram.cs
builder.Services.AddTransient<DetailPage>();
builder.Services.AddTransient<DetailViewModel>();

// Route registration (AppShell.xaml.cs or startup)
Routing.RegisterRoute(nameof(DetailPage), typeof(DetailPage));

// Navigation — DI resolves DetailPage and its DetailViewModel
await Shell.Current.GoToAsync(nameof(DetailPage));

Explicit Resolution

When constructor injection is not available, resolve services explicitly:

// From any Element with a Handler
var service = this.Handler.MauiContext.Services.GetService<IDataService>();

IServiceProvider Injection

Inject IServiceProvider when you need to resolve services dynamically:

public class MyService
{
    private readonly IServiceProvider _serviceProvider;

    public MyService(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    public void DoWork()
    {
        var api = _serviceProvider.GetRequiredService<IApiClient>();
    }
}

Platform-Specific Service Registration

Use preprocessor directives to register platform-specific implementations:

// In MauiProgram.cs
#if ANDROID
builder.Services.AddSingleton<INotificationService, AndroidNotificationService>();
#elif IOS || MACCATALYST
builder.Services.AddSingleton<INotificationService, AppleNotificationService>();
#elif WINDOWS
builder.Services.AddSingleton<INotificationService, WindowsNotificationService>();
#endif

Interface-First Pattern for Testability

Define interfaces for services so implementations can be swapped in tests:

public interface IDataService
{
    Task<List<Item>> GetItemsAsync();
}

public class DataService : IDataService
{
    public async Task<List<Item>> GetItemsAsync() { /* ... */ }
}

// Register the interface → implementation mapping
builder.Services.AddSingleton<IDataService, DataService>();

In tests, substitute a mock without touching production code:

var services = new ServiceCollection();
services.AddSingleton<IDataService, FakeDataService>();

Gotcha: XAML Resource Parsing vs. DI Timing

XAML resources (styles, resource dictionaries in App.xaml) are parsed before the App class is fully resolved from the container. If a resource or converter needs a service, inject IServiceProvider into the App constructor and resolve what you need in CreateWindow():

public partial class App : Application
{
    private readonly IServiceProvider _services;

    public App(IServiceProvider services)
    {
        _services = services;
        InitializeComponent(); // XAML resources parse here
    }

    protected override Window CreateWindow(IActivationState? activationState)
    {
        // Safe to resolve services here — container is fully built
        var mainPage = _services.GetRequiredService<MainPage>();
        return new Window(new AppShell());
    }
}

Quick Checklist

• Register every Page and ViewModel you want injected in MauiProgram.cs.
• Prefer constructor injection over service-locator calls.
• Use AddSingleton only for truly shared or expensive services.
• Use interfaces for any service you want to mock in tests.
• Use #if directives for platform-specific implementations.
• Resolve late-bound services in CreateWindow(), not during XAML parse.