Dependency Injection is Returning Null

Question

Forgive me, I'm new to the model/view model structure. I am trying to call a dependency to a method (IAuthenticationService) and it returns as null and I am unsure why. I tried adjusting a few of my methods and it still returns null. Any help is much appreciated. I am using .net MAUI.

The service I made.

public interface IAuthenticationService
    {
        User User { get; set; }
        Task Update(int userId, string firstName, string lastname);

    }

    public class AuthenticationService : IAuthenticationService
    {
        private IHttpService _httpService;
        private NavigationManager _navigationManager;
        private ILocalStorageService _localStorageService;

        public User User { get;  set; }

        public AuthenticationService(
            IHttpService httpService,
            NavigationManager navigationManager,
            ILocalStorageService localStorageService
        ) {
            _httpService = httpService;
            _navigationManager = navigationManager;
            _localStorageService = localStorageService;
        }

        public async Task Update(int userId, string firstName, string lastname)
        {

                User = await _httpService.Put<User>($"URL{userId}", new { firstName, lastname});
                var output = JsonSerializer.Serialize(User);
                await SecureStorage.SetAsync("UserInfo", output);

        }

    }

My MauiProgram.cs

 var builder = MauiApp.CreateBuilder();
        builder
            .UseSkiaSharp()
            .UseMauiApp<App>().UseMauiCommunityToolkit()
            .ConfigureFonts(fonts =>
            {
                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
            });
        builder.Services
                .AddScoped<IAuthenticationService, AuthenticationService>()
                .AddScoped<IUserService, UserService>()
                .AddScoped<IHttpService, HttpService>()
                .AddScoped<ILocalStorageService, LocalStorageService>();

        builder.Services.AddScoped(x => {
            var apirl = new Uri("URL");


            return new HttpClient() { BaseAddress = apiUrl };
        });


        builder.Services.AddMauiBlazorWebView();
        #if DEBUG
        builder.Services.AddBlazorWebViewDeveloperTools();
#endif
        
        builder.Services.AddSingleton<WeatherForecastService>();


        return builder.Build();

Where Im trying to call it.

public partial class ProfileInformation : ContentPage
{
    IAuthenticationService AuthenticationService;
    private User user = new User();
    public ProfileInformation()
    {
        InitializeComponent();

    }

    async void Button2_Clicked(object sender, EventArgs e)
    {
int id = "1"
string namef = "test"
string namel = "test"
        var test = AuthenticationService.Update(id, namef, namel);
        
    }

The above line var test, authentication service returns null.

I have tried creating a ViewModel with the same structure and it still fails. I am at a loss and cant find where I went wrong, I have read multiple articles and have tried what they mentioned and it still returns null. I know for a fact it's something on my end. I just cant find why.

Answer 1

you need to include the parameter in your constructor

IAuthenticationService AuthenticationService;

public ProfileInformation(IAuthenticationService authService)
{
    InitializeComponent();

    this.AuthenticationService = authService;
}

Answer 2

I think that you have to inject your service in the constructor.

public partial class ProfileInformation : ContentPage
{
    IAuthenticationService AuthenticationService;
    private User user = new User();
    public ProfileInformation(IAuthenticationService authenticationService)
    {
        AuthenticationService = authenticationService;
        InitializeComponent();

    }

    async void Button2_Clicked(object sender, EventArgs e)
    {
int id = "1"
string namef = "test"
string namel = "test"
        var test = AuthenticationService.Update(id, namef, namel);
        
    }