浅谈Android设计模式学习之观察者模式

public class MyPerson extends Observable {

  private String name;
  private int age;
  private String sex;

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
    setChanged();
    notifyObservers();
  }

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
    setChanged();
    notifyObservers();
  }

  public String getSex() {
    return sex;
  }

  public void setSex(String sex) {
    this.sex = sex;
    setChanged();
    notifyObservers();
  }

  @Override
  public String toString() {
    return "MyPerson [name=" + name + ", age=" + age + ", sex=" + sex + "]";
  }
}

public class MyObserver implements Observer {

  private int id;
  private MyPerson myPerson;

  public MyObserver(int id) {
    System.out.println("我是观察者---->" + id);
    this.id = id;
  }

  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public MyPerson getMyPerson() {
    return myPerson;
  }

  public void setMyPerson(MyPerson myPerson) {
    this.myPerson = myPerson;
  }

  @Override
  public void update(Observable observable, Object data) {
    System.out.println("观察者---->" + id + "得到更新");
    this.myPerson = (MyPerson) observable;
    System.out.println(((MyPerson) observable).toString());
  }

}

public class MainActivity extends Activity {

  private Button btnAddObserver;
  private Button btnChangeData;
  private MyPerson observable;
  private MyObserver myObserver;
  private List myObservers;
  private ListView listview;

  private int i;

  private Handler handler = new Handler() {
    public void handleMessage(android.os.Message msg) {
      MyListAdapter myListAdapter = new MyListAdapter(MainActivity.this,
          myObservers);
      listview.setAdapter(myListAdapter);

    };
  };

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btnAddObserver = (Button) findViewById(R.id.btn_add_observer);
    btnChangeData = (Button) findViewById(R.id.btn_change_data);
    listview = getListView();

    observable = new MyPerson();
    myObservers = new ArrayList();

    btnAddObserver.setOnClickListener(new OnClickListener() {

      @Override
      public void onClick(View v) {
        myObserver = new MyObserver(i);
        i++;
        observable.addObserver(myObserver);
        myObservers.add(myObserver);
        handler.sendEmptyMessage(0);
      }
    });

    btnChangeData.setOnClickListener(new OnClickListener() {

      @Override
      public void onClick(View v) {
        observable.setName("a" + i);
        observable.setAge(10 + i);
        observable.setSex("男" + i);
        handler.sendEmptyMessage(0);
      }
    });

  }

  @Override
  protected void onDestroy() {
    // TODO Auto-generated method stub
    super.onDestroy();
    observable.deleteObserver(myObserver);
  }
}

public abstract class BaseAdapter implements ListAdapter, SpinnerAdapter {
  // 数据集观察者
  private final DataSetObservable mDataSetObservable = new DataSetObservable();

  // 代码省略

  public void registerDataSetObserver(DataSetObserver observer) {
    mDataSetObservable.registerObserver(observer);
  }

  public void unregisterDataSetObserver(DataSetObserver observer) {
    mDataSetObservable.unregisterObserver(observer);
  }

  /**
   * Notifies the attached observers that the underlying data has been changed
   * and any View reflecting the data set should refresh itself.
   * 当数据集用变化时通知所有观察者
   */
  public void notifyDataSetChanged() {
    mDataSetObservable.notifyChanged();
  }
}

public class DataSetObservable extends Observable {
  /**
   * Invokes onChanged on each observer. Called when the data set being observed has
   * changed, and which when read contains the new state of the data.
   */
  public void notifyChanged() {
    synchronized(mObservers) {
      // 调用所有观察者的onChanged方式
      for (int i = mObservers.size() - 1; i >= 0; i--) {
        mObservers.get(i).onChanged();
      }
    }
  }

}

 @Override
  public void setAdapter(ListAdapter adapter) {
    // 如果已经有了一个adapter,那么先注销该Adapter对应的观察者
    if (mAdapter != null && mDataSetObserver != null) {
      mAdapter.unregisterDataSetObserver(mDataSetObserver);
    }

    // 代码省略

    super.setAdapter(adapter);

    if (mAdapter != null) {
      mAreAllItemsSelectable = mAdapter.areAllItemsEnabled();
      mOldItemCount = mItemCount;
      // 获取数据的数量
      mItemCount = mAdapter.getCount();
      checkFocus();
      // 注意这里 : 创建一个一个数据集观察者
      mDataSetObserver = new AdapterDataSetObserver();
      // 将这个观察者注册到Adapter中，实际上是注册到DataSetObservable中
      mAdapter.registerDataSetObserver(mDataSetObserver);

      // 代码省略
    } else {
      // 代码省略
    }

    requestLayout();
  }

 class AdapterDataSetObserver extends AdapterView.AdapterDataSetObserver {
    @Override
    public void onChanged() {
      super.onChanged();
      if (mFastScroll != null) {
        mFastScroll.onSectionsChanged();
      }
    }

    @Override
    public void onInvalidated() {
      super.onInvalidated();
      if (mFastScroll != null) {
        mFastScroll.onSectionsChanged();
      }
    }
  }

class AdapterDataSetObserver extends DataSetObserver {

    private Parcelable mInstanceState = null;
    // 调用Adapter的notifyDataSetChanged的时候会调用所有观察者的onChanged方法,核心实现就在这里
    @Override
    public void onChanged() {
      mDataChanged = true;
      mOldItemCount = mItemCount;
      // 获取Adapter中数据的数量
      mItemCount = getAdapter().getCount();

      // Detect the case where a cursor that was previously invalidated has
      // been repopulated with new data.
      if (AdapterView.this.getAdapter().hasStableIds() && mInstanceState != null
          && mOldItemCount == 0 && mItemCount > 0) {
        AdapterView.this.onRestoreInstanceState(mInstanceState);
        mInstanceState = null;
      } else {
        rememberSyncState();
      }
      checkFocus();
      // 重新布局ListView、GridView等AdapterView组件
      requestLayout();
    }

    // 代码省略

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