public void OnClosing(ViewModelClosingEventArgs e)
 {
     var handler = Closing;
     if (handler != null) handler(this, e);
 }
 protected virtual bool RaiseClosing(object parameter)
 {
     var handler = Closing;
     if (handler == null)
         return true;
     var args = new ViewModelClosingEventArgs(this, parameter);
     handler(this, args);
     return !args.Cancel;
 }