观察者模式 android 更新UI

原来的网址：http://malong26.iteye.com/blog/1858724

android的app程序退出有几种方式：activity队列方式、广播方式。在这里介绍一下我实现该功能的方式--观察者模式。 
    方法的大概思路为：建立Activity基类，实现观察者接口，实现监听方法，finish掉本实例；在Application里面单例一个目标对象，当需要关闭程序的时候，调用目标对象的通知方法，通知所有观察者。 
    代码如下： 
观察者接口 

public interface Observer {
    public void update(Subject subject);
}

目标对象基类 

public class Subject {
    private List<Observer> observers = new ArrayList<Observer>();

    public void attach(Observer observer){
        observers.add(observer);
    }

    public void detach(Observer observer){
        observers.remove(observer);
    }

    protected void notifyObservers(){
        for(Observer observer : observers){
            observer.update(this);
        }
    }
}

目标对象子类(实现具体退出方法) 

public class ApplicationSubject extends Subject {
    public void exit(){
        notifyObservers();
    }
}

MyApplication类(在Manifest文件中将标签application的name改为本类的全限定名) 

public class MyApplication extends Application {

    private static ApplicationSubject applicationSubject;

    public ApplicationSubject getApplicationSubject() {
                if(applicationSubject == null) applicationSubject = new ApplicationSubject();
        return applicationSubject;
    }

}

Activity基类 

public abstract class BaseActivity extends Activity implements Observer {

    public MyApplication app;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        app = (MyApplication) this.getApplication();
        app.getApplicationSubject().attach(this);
    }

    @Override
    public void finish() {
        // TODO Auto-generated method stub
                app.getApplicationSubject().detach(this);
        super.finish();
    }

    /**
     * 关闭程序
     */
    public void close() {
        app.getApplicationSubject().exit();
    };

    @Override
    public void update(Subject subject) {
        // TODO Auto-generated method stub
        this.finish();
    }

}

写几个测试页面测试一下 

public class ATestActivity extends BaseActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        startActivity(new Intent(this, BTestActivity.class));
    }
}
public class BTestActivity extends BaseActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        close(); //在BTestActivity中调用close方法，发现A和B都关闭了
    }
}