title: WPF. How hide/show main window from another window
body: <p>I have Two windows MainWindow and Login.
  The button which shows login located on mainWindow</p>
  
  <pre><code>this.Hide();
          Login li = new Login();
          li.Show();
  </code></pre>
  
  <p>on Login Window is button which checks password how i can show MainWindow if password is correct?</p>