虽然模型不了解视图的任何详细信息，但是模型和视图之间存在“观察者”关系。换句话说，视图保留对模型的引用并将其自身注册到模型以接收更改通知。接收到通知后，视图将从模型中获取新数据并对 UI 进行更新。(Although the model does not understand any of the details of the view, there is an observer relationship between the model and the view. In other words, the view retains the reference to the model and registers itself into the model to receive the change notification. Upon receipt of the notification, the view will retrieve new data from the model and update the UI.)