Retrieving all Window classes in WPF by reflection?

I have WPF project that I use for test purposes, for every Window I create I add new button in the start window, I want to change this and add the buttons dynamically by reflection, I tried this:

public partial class _DynamicWindow : Window
    {
        StackPanel stack = new StackPanel();
        public _DynamicWindow()
        {
            InitializeComponent();
            RetrieveAll();
        }

        private void RetrieveAll()
        {
            foreach (var window in Assembly.GetAssembly(typeof(Window)).GetTypes())
            {
                CreateButton(window);
            }
        }

        private void CreateButton(Type window)
        {
            var obj = Activator.CreateInstance(window) as Window;
            Button btnShow = new Button();
            btnShow.Click += delegate { obj.Show(); };
            btnShow.Content = obj.Name;
            stack.Children.Add(btnShow);
        }
    }

but I get this error:

System.Windows.Markup.XamlParseException: ''The invocation of the constructor on type 'WPFTest._DynamicWindow' that matches the specified binding constraints threw an exception.' Line number '6' and line position '9'.'

ArgumentException: Cannot create an instance of <>f__AnonymousType0`1[j__TPar] because Type.ContainsGenericParameters is true.