public interface IMainWindow 
    {
        string FolderPatch { get;}
        event EventHandler OpenFileDialog;
    }
    /// <summary>
    /// Логика взаимодействия для MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window, IMainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
        }
 
        public string FolderPatch
        {
            get { return textBox1.Text; }
        }
 
        public event EventHandler OpenFileDialog;
 
        private void button1_Click(object sender, RoutedEventArgs e)
        {
            if (OpenFileDialog != null) OpenFileDialog(this, EventArgs.Empty);
        }
    }

public class MyClass
    {
        private readonly IMainWindow _view;
 
        public MainPresentor(IMainWindow view)
        {
            _view = view;
            _view.OpenFileDialog += new EventHandler(_view_OpenFileDialog);
        }
 
        void _view_OpenFileDialog(object sender, EventArgs e)
        {
            //код
        }
    }

public MainWindow()
        {
            InitializeComponent();
            MainWindow window = new MainWindow();
            MyClass MP = new MyClass(window);
        }