public static DoctorMainWindow GetInstance(Doctor loggedDoctor)
 {
     if (instance == null)
     {
         instance = new DoctorMainWindow(loggedDoctor);
     }
     return(instance);
 }
 private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
 {
     MainWindow.Serialize();
     instance = null;
 }