StTest/MyTests/MainWindow.xaml.cs

using System.Windows;
using System.Windows.Input;

namespace MyTests
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            MainFrame.Content = new Pages.LoginPage();
        }

        #region Кнопки закрытия и скрытия приложения
        private void Border_MouseDown(object sender, MouseButtonEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
                DragMove(); // Возможность перетаскивать
        }

        private void ButtonMininize_Click(object sender, RoutedEventArgs e)
        {
            Application.Current.MainWindow.WindowState = WindowState.Minimized; //Скрытие
        }

        private void WindowStateButton_Click(object sender, RoutedEventArgs e)
        {
            if (Application.Current.MainWindow.WindowState != WindowState.Maximized)
                Application.Current.MainWindow.WindowState = WindowState.Maximized;
            else
                Application.Current.MainWindow.WindowState = WindowState.Normal;
        }

        private void CloseButton_Click(object sender, RoutedEventArgs e)
        {
            Application.Current.Shutdown(); // Закрытие программы
        }
        #endregion

    }
}