BackgroundBuilder/App.xaml.cs

using System;
using System.Windows;
using BackgroundBuilder.Repositories;
using BackgroundBuilder.Services;
using BackgroundBuilder.ViewModels;
using BackgroundBuilder.Views;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace BackgroundBuilder
{
    public partial class App : Application
    {
        private readonly IHost _host;

        public App()
        {
            _host = Host.CreateDefaultBuilder()
                .ConfigureAppConfiguration(cfg =>
                    cfg.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true))
                .ConfigureServices((_, services) =>
                {
                    // Database & repository
                    services.AddSingleton<DatabaseService>();
                    services.AddScoped<IContatoRepository, PostgresContatoRepository>();

                    // New image service
                    services.AddSingleton<IImageService, ImageService>();
                    
                    // New taskbar service
                    services.AddSingleton<ITaskbarService, TaskbarService>();

                    // VM & View
                    services.AddTransient<MainWindowViewModel>();
                    services.AddTransient<MainWindow>();
                })
                .Build();
        }

        private async void OnStartup(object sender, StartupEventArgs e)
        {
            await _host.StartAsync();
            var window = _host.Services.GetRequiredService<MainWindow>();
            window.Show();
        }

        protected override async void OnExit(ExitEventArgs e)
        {
            using (_host) { await _host.StopAsync(); }
            base.OnExit(e);
        }
    }
}