一個簡單的觀察者模式例子

一：下面的這個類是核心類
public class NotificationCenter {

//static reference for singleton
private static NotificationCenter _instance;
private static NotificationCenter _instance2;
private HashMap<String, ArrayList<NotificationDelegate>> registredObjects;

//default c'tor for singleton
private NotificationCenter(){
    registredObjects = new HashMap<>();
}
//returning the reference
public static synchronized NotificationCenter defaultCenter(){
    if(_instance == null)
        _instance = new NotificationCenter();
    return _instance;
}
//returning the reference
public static synchronized NotificationCenter defaultCenterNew(){
    if(_instance2 == null)
        _instance2 = new NotificationCenter();
    return _instance2;
}

public synchronized void addFucntionForNotification(String notificationName, NotificationDelegate delegate){
    ArrayList<NotificationDelegate> list = registredObjects.get(notificationName);
    if(list == null) {
        list = new ArrayList<>();
        registredObjects.put(notificationName, list);
    }
    list.add(delegate);
}

public synchronized void removeFucntionForNotification(String notificationName, NotificationDelegate r){
    if(registredObjects == null){
        return ;
    }
    ArrayList<NotificationDelegate> list = registredObjects.get(notificationName);
    if(list != null) {
        list.remove(r);
    }
}

public synchronized void postNotificationName(String notificationName, Object obj){
    ArrayList<NotificationDelegate> list = registredObjects.get(notificationName);

// LogUtils.showLog(“==========”,” ” + list);
if(list != null) {
for(NotificationDelegate r: list){
r.update(notificationName,obj);
// LogUtils.showLog(“==========”,” upadate “);
}

    }
}

// public synchronized void postNotification(Object obj){
// for(String name: registredObjects.keySet()){
// ArrayList list = registredObjects.get(name);
// if(list!= null){
// for(NotificationDelegate r: list)
// r.update(“”,obj);
// }
// }
// }

}
二：
/**
* Created by dongwanlin on 2016/6/2.
*/
public interface NotificationDelegate {
public void update(String name, Object obj);
}

三：
( 1 )傳送
SmmApplication.center.postNotificationName(FinalConstant.AutoQuotation_Finish, categoryId);
（2）接收
private void registerListener() {
final Gson gson = new Gson();
// 實時更新監聽器
delegate = new NotificationDelegate() {
@Override
public void update(String name, Object obj) {
if (name.equals(FinalConstant.AutoQuotation_Finish)) {
s_page = 1;
getData();
}
}
};
if (SmmApplication.center != null) { SmmApplication.center.addFucntionForNotification(FinalConstant.AutoQuotation_Finish,delegate);
}
}
@Override
public void onDestroy() {
super.onDestroy();
if (SmmApplication.center != null) {
SmmApplication.center.removeFucntionForNotification(FinalConstant.AutoQuotation_Finish, delegate);
}
}