Dependency Injection on ViewModels

[jaymarvels]

I have a User control (ReacticeUserControl) that I created a ViewModel for:

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

    public MyViewModel() 
    {
        Exit = ReactiveCommand.Create(ExitApplication);
    }

    private void ExitApplication() 
    {
        Locator.Current.GetService<IApplication>()?.Shutdown();
    }
}

I instantiate it in the ReacticeUserControl code behind:

    {
        //window = TopLevel.GetTopLevel(this) as Window;
        window = this.GetVisualRoot() as Window;
        this.DataContext = new MyViewModel();
        base.OnLoaded(e);
    }

All good so far.

If I now want to inject a dependency into the ViewModel like so:

    public MyViewModel(IRepository<CityModel> cityRepository) 
  {
        _cityRepository = cityRepository;
        Exit = ReactiveCommand.Create(ExitApplication);
    }

This means when I try to instantiate it requires this parameter and kind of defeats the point of DI. In my App code behind I have set up the configuration needed:

    public  App() 
    {
        // Let's do this in the constructor
        AppHost = Host.CreateDefaultBuilder()
            .UseContentRoot(AppContext.BaseDirectory)
            .ConfigureServices((context, services) => {
                // Register services with the DI container here.
                services.ConfigureFrameworkServices();
            })
            .Build();
    }

Just feel like I am missing or have missed a step somewhere, trying to keep things lightweight and only use ViewModels where needed

[timunie]

check Avalonia.Samples -> ViewInteractionSample

[jaymarvels]

Appreciate the swift response but in that example none of the viewmodels have any dependencies so unsure how this relates to my issue

[timunie]

Thought you wanted to exit your App. Otherwise DI works as it does anywhere, for example using MS DI or RxUI Splat

[jaymarvels]

Hi Tim,

Sorry I must not have explained well.

Exit app is all good, my issues are around constructor injection.

I register my services: services.ConfigureFrameworkServices(); , which happens to include services.AddTransient<IRepository<CityModel>, CityRepository>();

In my ViewModel I can inject:

    public MyViewModel(IRepository<CityModel> cityRepository) 
{
        _cityRepository = cityRepository;
        Exit = ReactiveCommand.Create(ExitApplication);
    }

Problem is when trying to instantiate the ViewModel in the View code behind: this.DataContext = new MyViewModel(); with the injected constructor here at the code behind point its expecting "CityRepository" which defeats the point of using dependency injection.

Feels like I am almost there but just missing something or a step

[jaymarvels]

I think this is my issue, coming from a asp.net core background I was just expecting after some initial set up against the Host.CreateDefaultBuilder() that that would be enough, but looking through the docs and watching AngelSix it looks like the DI service registration is needed within the OnFrameworkInitializationCompleted

[thevortexcloud]

You can technically register the services elsewhere (EG in the AfterSetup method). But that is the easiest place to do it.

[LSXAxeller]

you can follow the avalonia docs guide , I applied it in Program.cs like this, and it's working like charm

public static void Main(string[] args)
{
    Log.Logger = new LoggerConfiguration()
        .Enrich.FromLogContext()
        .WriteTo.File("EGOIST_Handler.log", rollingInterval: RollingInterval.Month)
        .CreateLogger();

    var services = new ServiceCollection();
    var provider = services
        .AddLogging(loggingBuilder => loggingBuilder.AddSerilog(dispose: true))
        .AddKeyedSingleton<ITextService, ChatService>("ChatService")
        .AddKeyedSingleton<IModelsRepository, LocalModelsRepository>("LocalModelsRepository")
        .AddKeyedSingleton<IModelsRepository, HuggingFaceModelsRepository>("HuggingFaceModelsRepository")
        .AddKeyedSingleton<IModelsRepository, CivitAIModelsRepository>("CivitAIModelsRepository")
        .AddSingleton<MainWindowViewModel>()
        .AddSingleton<MainWindow>()
        .AddTransient<HomePageViewModel>()
        .AddTransient<HomePageView>()
        .AddTransient<TextPageViewModel>()
        .AddTransient<ChatPageViewModel>()
        .AddTransient<ChatPageView>()
        .BuildServiceProvider();
    Ioc.Default.ConfigureServices(provider);

    BuildAvaloniaApp()
    .StartWithClassicDesktopLifetime(args);
}

and if needed, you can get your services from anywhere in code like Ioc.Default.GetService<MainWindowViewModel>();

[thevortexcloud]

You are doing some things the Avalonia guide does not. Specifically you are setting up a static locator. The original guide did do this as when I wrote the code I designed it to work across projects so it would work on every platform Avalonia supports. But what's there now only shows you how to set up DI without a locator (which is how you should be using it anyway in 99% of cases) in a single project. The locator should only ever be used when you have no other option as it creates lots of coupling.

[LSXAxeller]

I don't use the locator myself, as I wrote if needed, I am prefering to inject like I do in ASP.NET, in addition that I write in Program.cs since I am targeting Desktop only so I have one presentation project, but thanks for reminding me about the coupling it cause.