Avalonia/samples/GpuInterop/App.axaml.cs

using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Markup.Xaml;

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

        public override void OnFrameworkInitializationCompleted()
        {
            if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktopLifetime)
            {
                desktopLifetime.MainWindow = new MainWindow();
            }
        }
    }
}