在Android中观察者模式的简单使用

public class MyApplication extends Application {

    private List<Activity> activityList = new LinkedList<Activity>();
    private static MyApplication instance;

    private MyApplication(){
    }

    //单例模式中获取唯一的MyApplication实例
    public static MyApplication getInstance() {
        if(null == instance){
            instance = new MyApplication();
        }
        return instance;
    }

    //添加Activity到容器中
    public void addActivity(Activity activity){
        activityList.add(activity);
    }

    //遍历所有Activity并finish
    public void exit(){
        for(Activity activity:activityList){
            activity.finish();
        }
        System.exit(0);
    }
}