// show register window
private void Register_the_patient_handler(object sender, RoutedEventArgs e)
{
this.Hide();
Przychodnia.RegisterWindow registerWindow = new RegisterWindow();
registerWindow.Show();
}
// show register window
private void Register(object sender, RoutedEventArgs e)
{
Przychodnia.RegisterWindow register = new RegisterWindow();
this.Close();
register.Show();
}