App.axaml.cs

using System.Linq;
using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Data.Core.Plugins;
using Avalonia.Markup.Xaml;
using PostCodeSerialMonitor.ViewModels;
using PostCodeSerialMonitor.Views;
using Microsoft.Extensions.DependencyInjection;

namespace PostCodeSerialMonitor;

public partial class App : Application
{
    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this);
    }

    public override void OnFrameworkInitializationCompleted()
    {
        // If you use CommunityToolkit, line below is needed to remove Avalonia data validation.
        // Without this line you will get duplicate validations from both Avalonia and CT
        BindingPlugins.DataValidators.RemoveAt(0);

        // Register all the services needed for the application to run
        var collection = new ServiceCollection();
        collection.AddCommonServices();

        // Creates a ServiceProvider containing services from the provided IServiceCollection
        var services = collection.BuildServiceProvider();

        var mainWindowViewModel = services.GetRequiredService<MainWindowViewModel>();

        //@todo Load language setting in cofig.json.
        //
        //Assets.Resources.Culture = new CultureInfo("en-US");

        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            // Avoid duplicate validations from both Avalonia and the CommunityToolkit. 
            // More info: https://docs.avaloniaui.net/docs/guides/development-guides/data-validation#manage-validationplugins
            DisableAvaloniaDataAnnotationValidation();

            desktop.MainWindow = new MainWindow
            {
                DataContext = mainWindowViewModel,
            };
        }

        base.OnFrameworkInitializationCompleted();
    }

    private void DisableAvaloniaDataAnnotationValidation()
    {
        // Get an array of plugins to remove
        var dataValidationPluginsToRemove =
            BindingPlugins.DataValidators.OfType<DataAnnotationsValidationPlugin>().ToArray();

        // remove each entry found
        foreach (var plugin in dataValidationPluginsToRemove)
        {
            BindingPlugins.DataValidators.Remove(plugin);
        }
    }
}