//被觀察者
 public class Wechat extends Observable{
  public void postNewPublication(String content){
   setChanged();
   notifyObservers(content);
  }
 }

 //觀察者
 public class Reader implements Observer{
  public String name ;

  public Reader(String name) {
   this.name = name;
  }

  @Override
  public void update(Observable o, Object arg) {
   Log.i(TAG, "update: wechat is update content is :"+arg);
  }
 }
 
 public void test(){
  Wechat wechat=new Wechat();
  
  Reader reader1=new Reader("reader1");
  Reader reader2=new Reader("reader2");
  Reader reader3=new Reader("reader3");
  
  wechat.addObserver(reader1);
  wechat.addObserver(reader2);
  wechat.addObserver(reader3);
  
  wechat.postNewPublication("up up up");
 }

 public void notifyDataSetChanged() {
  mDataSetObservable.notifyChanged();
 }

private final DataSetObservable mDataSetObservable = new DataSetObservable();

public class DataSetObservable extends Observable<DataSetObserver> {

public void notifyChanged() {
  synchronized(mObservers) {
   for (int i = mObservers.size() - 1; i >= 0; i--) {
    mObservers.get(i).onChanged();
   }
  }
 }
 }

class AdapterDataSetObserver extends DataSetObserver {
  private Parcelable mInstanceState = null;
  @Override
  public void onChanged() {
   mDataChanged = true;
   mOldItemCount = mItemCount;
   mItemCount = getAdapter().getCount();
   if (AdapterView.this.getAdapter().hasStableIds() && mInstanceState != null
     && mOldItemCount == 0 && mItemCount > 0) {
    AdapterView.this.onRestoreInstanceState(mInstanceState);
    mInstanceState = null;
   } else {
    rememberSyncState();
   }
   checkFocus();
   //重新布局
   requestLayout();
  }

  ...

  public void clearSavedState() {
   mInstanceState = null;
  }
 }