Android多进程之Binder解绑监听的问题

Android多进程系列

• Android 多进程通信之几个基本问题
• Android多进程之Binder的使用
• Android多进程之手动编写Binder类

接上一篇文章《Android多进程之手动编写Binder类》中向服务端注册监听事件的问题，在扩展了Binder类后，我们还需要改造对应的服务端和客户端

客户端和服务端的改造

服务端改造

• 增加注册监听接口的功能

private CopyOnWriteArrayList<IOnNewBookArrivedListener> mListenerList = new CopyOnWriteArrayList<IOnNewBookArrivedListener>(); private Binder mBinder = new BookManagerImpl(){ @Override public List<Book> getBookList() throws RemoteException { Log.e(TAG, "getBookList-->"+ System.currentTimeMillis()); return mBookList; } @Override public void addBook(Book book) throws RemoteException { Log.e(TAG, "addBook-->"); mBookList.add(book); } @Override public void registerListener(IOnNewBookArrivedListener listener) { if (!mListenerList.contains(listener)) { mListenerList.add(listener); }else { Log.e(TAG, "already exists"); } Log.e(TAG, "registerListener, size:"+mListenerList.size()); } @Override public void unRegisterListener(IOnNewBookArrivedListener listener) { if (mListenerList.contains(listener)) { mListenerList.remove(listener); Log.e(TAG, "unRegisterListener listener succeed"); }else { Log.e(TAG, "not found, can not unregister"); } Log.e(TAG, "unRegisterListener, current size:"+mListenerList.size()); } };

• 添加一个任务，定时像书籍列表中添加一本书，并触发通知客户端的操作

@Override public void onCreate() { super.onCreate(); Log.e(TAG, "onCreate-->"+ System.currentTimeMillis()); mBookList.add(new Book(1, "Android")); mBookList.add(new Book(2, "IOS")); new Thread(new ServiceWorker()).start(); } private void onNewBookArrived(Book book) throws RemoteException{ mBookList.add(book); Log.e(TAG, "new book arrived, notify listeners:" + mListenerList.size()); for (int i=0; i<mListenerList.size(); i++) { IOnNewBookArrivedListener listener = mListenerList.get(i); Log.e(TAG, "new book arrived, notify listener:" + listener); listener.onNewBookArrived(book); } } private class ServiceWorker implements Runnable { @Override public void run() { while (!mIsServiceDestoryed.get()) { try { Thread.sleep(5000); }catch (InterruptedException e) { e.printStackTrace(); } int bookId = mBookList.size() + 1; Book newBook = new Book(bookId, "new book#" + bookId); try { onNewBookArrived(newBook); }catch (RemoteException e) { e.printStackTrace(); } } } }

• 通知客户端的过程就是调用每个注册的监听接口的onNewBookArrived方法，也就是一个服务端调用客户端的过程，分别是调用onNewBookArrived-->onTransact-->Proxy的onNewBookArrived-->客户端

客户端改造

• 首先要声明一个IOnNewBookArrivedListener对象，并注册到服务端中

private IBookManager mRemoteBookManager; private ServiceConnection mConnection = new ServiceConnection() { @Override public void onServiceConnected(ComponentName componentName, IBinder iBinder) { Log.e(TAG, "ServiceConnection-->"+ System.currentTimeMillis()); IBookManager bookManager = BookManagerImpl.asInterface(iBinder); mRemoteBookManager = bookManager; try { List<Book> list = bookManager.getBookList(); Log.e(TAG, "query book list, list type:" + list.getClass().getCanonicalName()); Log.e(TAG, "query book list:" + list.toString()); Book newBook = new Book(3, "Android 进阶"); bookManager.addBook(newBook); Log.e(TAG, "add book:" + newBook); List<Book> newList = bookManager.getBookList(); Log.e(TAG, "query book list:" + newList.toString()); bookManager.registerListener(mOnNewBookArrivedListener); } catch (RemoteException e) { e.printStackTrace(); } } @Override public void onServiceDisconnected(ComponentName componentName) { mRemoteBookManager = null; Log.e(TAG, "binder died"); } }; /** * 这个方法运行在客户端的binder线程池中，不能直接进行UI操作 */ private IOnNewBookArrivedListener mOnNewBookArrivedListener = new OnNewBookArrivedListenerImpl(){ @Override public void onNewBookArrived(Book book) { mHandler.obtainMessage(MESSAGE_NEW_BOOK_ARRIVED, book).sendToTarget(); } };

• 然后由于客户端的IOnNewBookArrivedListener回调方法onNewBookArrived运行在Binder线程池中，所以需要一个Handler来切换到UI线程

private static final int MESSAGE_NEW_BOOK_ARRIVED = 1; private Handler mHandler = new Handler() { @Override public void handleMessage(Message message) { switch (message.what) { case MESSAGE_NEW_BOOK_ARRIVED: Log.e(TAG, "receive new book:" + message.obj); break; default: super.handleMessage(message); } } };

• 最后需要在客户端退出时解除服务端的注册监听

@Override protected void onDestroy() { if (mRemoteBookManager != null && mRemoteBookManager.asBinder().isBinderAlive()) { try { Log.e(TAG, "unRegister listener:" + mOnNewBookArrivedListener); mRemoteBookManager.unRegisterListener(mOnNewBookArrivedListener); }catch (RemoteException e) { e.printStackTrace(); } } unbindService(mConnection); super.onDestroy(); }

改造结果

• 通过上图我们可以看到，我们已经成功实现了预期的功能，并且服务端通知客户端的调用过程也如我们上面所说的那样
• 接下去我们退出应用，这样可以测试解绑监听的功能
  
• 从上图我们可以看到，服务端调用解绑失败了，提示找不到接口，这是咋回事呢？

利用Binder进行进程间通信，Binder会把客户端传递的参数AIDL接口和Parcelable对象，重新转化并生成一个新的对象。因为对象是不能跨进程传输的，对象的跨进程传输本质上就是序列化和反序列化的过程。所以上述情况服务端根本就没有客户端的那个对象，那肯定找不到会解绑失败。那咋办呢？

RemoteCallBackList

RemoteCallBackList是啥

public class RemoteCallbackList<E extends IInterface> { /*package*/ ArrayMap<IBinder, Callback> mCallbacks = new ArrayMap<IBinder, Callback>(); ... }

• RemoteCallBackList的内部有一个Map结构用来保存所有的AIDL回调，这个Map的key是IBinder类型，value是CallBack类型

public boolean register(E callback, Object cookie) { synchronized (mCallbacks) { if (mKilled) { return false; } IBinder binder = callback.asBinder(); try { Callback cb = new Callback(callback, cookie); binder.linkToDeath(cb, 0); mCallbacks.put(binder, cb); return true; } catch (RemoteException e) { return false; } } }

• 每次有新的接口来，就调用register方法注册，添加到mCallbacks中
• 通过上面的源码我们可以看到，由于客户端跨进程传输的对象的底层的Binder对象都是同一个，所以我们可以通过这一点，当需要解除注册监听时，就可以通过遍历RemoteCallBackList找到与解绑客户端Binder对象相同的listener并删除即可
• 而且我们可以看到RemoteCallBackList中实现了线程同步，我们在利用它进行注册和解注册时不需要处理同步问题。
• 特别的是，客户端进程终止后，RemoteCallBackList能够自动解除客户端所注册的listener

用RemoteCallBackList实现实现解绑注册

private RemoteCallbackList<IOnNewBookArrivedListener> mListenerList = new RemoteCallbackList<IOnNewBookArrivedListener>(); private Binder mBinder = new BookManagerImpl(){ @Override public List<Book> getBookList() throws RemoteException { Log.e(TAG, "getBookList-->"+ System.currentTimeMillis()); return mBookList; } @Override public void addBook(Book book) throws RemoteException { Log.e(TAG, "addBook-->"); mBookList.add(book); } @Override public void registerListener(IOnNewBookArrivedListener listener) { //注册接口 mListenerList.register(listener); } @Override public void unRegisterListener(IOnNewBookArrivedListener listener) { //解注册接口 mListenerList.unregister(listener); } }; //通知客户端 private void onNewBookArrived(Book book) throws RemoteException{ mBookList.add(book); final int N = mListenerList.beginBroadcast(); for (int i=0; i<N; i++) { IOnNewBookArrivedListener listener = mListenerList.getBroadcastItem(i); if (listener != null) { try { listener.onNewBookArrived(book); }catch (RemoteException e) { e.printStackTrace(); } } } mListenerList.finishBroadcast(); }

• 通过RemoteCallBackList的改造，我们就可以成功解注册客户端的listener了

注意点

• RemoteCallBackList并不是一个List，我们无法像操作list一样操作它，比如调用size方法
• 遍历RemoteCallBackList必须按照上面代码中的方式进行，beginBroadcast方法和finishBroadcast方法必须配对使用

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