一个关于观察者模式的问题

[honglei92]

data.java

public class Data {
	private int dataChange;
	private String date;
	private Boolean isYejian;
	private int tihao;

DataChange.java

public class DataChange extends Observable {
	private static DataChange instance=null;

	public static DataChange getInstance() {
		if (null==instance) {
			instance=new DataChange();
		}
		return instance;
	}
	
	public void notifyDataChange(Data data)
	{
		setChanged();
		notifyObservers(data);
	}
	
}

DataWatcher.java

public abstract class DataWatcher  implements Observer {

	@Override
	public void update(Observable observable, Object data) {
		
	}

avtivityB中单击事件代码：

Data mData = new Data();
				mData.setTihao(position);
				DataChange.getInstance().notifyDataChange(mData);

activityA继承自fragmentactivity,
声明部分:

private DataWatcher watcher = new DataWatcher() {
		public void update(java.util.Observable observable, Object data) {
			super.update(observable, data);
			Data mData = (Data) data;
			tihao=mData.getTihao();
			Log.i("选中题号", "mData---->>" + mData.getTihao());
		}

	};

监听部分:

@Override
	protected void onResume() {
		super.onResume();
		DataChange.getInstance().addObserver(watcher);
		Log.i("执行了方法", "onResume");
	}

	@Override
	protected void onPause() {
		super.onPause();
		DataChange.getInstance().deleteObserver(watcher);
	}

但是就是watcher方法没被调用到，求大神解释。

[honglei92]

http://stackoverflow.com/questions/21428674/how-to-set-edittext-values-after-intent-back-to-old-activity