// Observer, the classes that need to use the observer pattern implement this interface
public interface Observer {
void update(Object... objs);
}
// Observed ( 1 Abstract class, easy to extend)
public abstract class Observable {
public final ArrayList<Class<?>> obserList = new ArrayList<Class<?>>();
/** Attach Observer (register an observer by instance)
* <b>Notice:</b> ob can't be null ,or it will throw NullPointerException
* */
public <T> void registerObserver(T ob) {
if (ob == null) throw new NullPointerException();
this.registerObserver(ob.getClass());
}
/**
* Attach Observer (by Class Registered observer)
* @param cls
*/
public void registerObserver(Class<?> cls) {
if (cls == null) throw new NullPointerException();
synchronized(obserList) {
if (!obserList.contains(cls)) {
obserList.add(cls);
}
}
}
/** Unattach Observer (unregister observer)
* <b>Notice:</b>
* <b>It reverses with attachObserver() method</b>
* */
public <T> void unRegisterObserver(T ob) {
if (ob == null) throw new NullPointerException();
this.unRegisterObserver(ob.getClass());
}
/** Unattach Observer (unregister the observer, sometimes used without getting an instance)
* <b>Notice:</b>
* <b>It reverses with attachObserver() method</b>
* */
public void unRegisterObserver(Class<?> cls) {
if(cls == null) throw new NullPointerException();
synchronized(obserList){
Iterator<Class<?>> iterator = obserList.iterator();
while(iterator.hasNext()) {
if(iterator.next().getName().equals(cls.getName())){
iterator.remove();
break;
}
}
}
}
/** detach all observers */
public void unRegisterAll() {
synchronized(obserList) {
obserList.clear();
}
}
/** Ruturn the size of observers */
public int countObservers() {
synchronized(obserList) {
return obserList.size();
}
}
/**
* notify all observer (notifies all observers, implemented in subclasses)
* @param objs
*/
public abstract void notifyObservers(Object... objs);
/**
* notify one certain observer Notice something, 1 A certain observer)
* @param cls
* @param objs
*/
public abstract void notifyObserver(Class<?> cls, Object... objs);
/**
* notify one certain observer
* @param cls
* @param objs
*/
public abstract <T> void notifyObserver(T t, Object... objs);
}
// Target observed
public class ConcreteObservable extends Observable {
private static ConcreteObservable instance = null;
private ConcreteObservable() {}
public static synchronized ConcreteObservable getInstance() {
if (instance == null) {
instance = new ConcreteObservable();
}
return instance;
}
@Override
public <T> void notifyObserver(T t, Object... objs) {
// TODO Auto-generated method stub
if (t == null) throw new NullPointerException();
this.notifyObserver(t.getClass(), objs);
}
@Override
public void notifyObservers(Object... objs) {
// TODO Auto-generated method stub
for (Class<?> cls : obserList) {
this.notifyObserver(cls, objs);
}
}
@Override // through java The reflection mechanism implements the call
public void notifyObserver(Class<?> cls, Object... objs) {
// TODO Auto-generated method stub
if (cls == null) throw new NullPointerException();
Method[] methods = cls.getDeclaredMethods();
for (Method method : methods) {
if (method.getName().equals("update")) {
try {
method.invoke(cls, objs);
break;
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
// use ( implementation Observer Interface)
public class Text extends Activity implements Observer {
public void onCreate(...) {
ConcreteObservable.getInstance().registerObserver(Text.class);
....
}
// Implement interface handling
public void update(Object... objs) {
// Do operations, like update data, update UI Etc.
}
}