Android 笔记:AIDL进阶

原文地址: http://tianma.space/post/3246519744/

在上一篇博客 Android 笔记:IPC - AIDL 中讲到的 IPC 方式之一 AIDL 的基本用法,本文主要记录一下 AIDL 的进阶。

AIDL 中的注册与反注册

之前的 IBookManager 中只提供了获取 书籍列表(getBookList) 和 添加书籍(addBook) 的方法,现在我们将其扩展一下,希望能加入“当新的书本被添加之后,能够通知出去”。这是一种 观察者模式

由于 AIDL 中无法使用普通接口,所以添加新的 IOnNewBookArrived.aidl 接口,用于回调新书的到来:

package com.github.tianma8023.ipclearn.aidl;

import com.github.tianma8023.ipclearn.aidl.Book;

interface IOnNewBookArrivedListener {
    void onNewBookArrived(in Book newBook);
}

IBookManager.aidl 接口中添加新的注册监听/取消监听的方法:

package com.github.tianma8023.ipclearn.aidl;

import com.github.tianma8023.ipclearn.aidl.Book;
import com.github.tianma8023.ipclearn.aidl.IOnNewBookArrivedListener;

interface IBookManager {
    List getBookList();
    void addBook(in Book book);

    void registerListener(IOnNewBookArrivedListener listener);
    void unregisterListener(IOnNewBookArrivedListener listener);
}

远程服务端实现 BookManagerService, 实现新加的两个方法,在 Service 中开启线程,定时加入一本新书通知所有注册者:

public class BookManagerService extends Service {
    private static final String TAG = "BMS";

    // 当前Service是否被销毁
    private AtomicBoolean mIsServiceDestroyed = new AtomicBoolean(false);
    // 书籍列表
    private CopyOnWriteArrayList mBookList = new CopyOnWriteArrayList<>();
    // 观察者列表
    private CopyOnWriteArrayList mListenerList = new CopyOnWriteArrayList<>();

    private Binder mBinder = new IBookManager.Stub() {
        @Override
        public List getBookList() throws RemoteException {
            return mBookList;      
        }

        @Override
        public void addBook(Book book) throws RemoteException {
            mBookList.add(book);
        }

        @Override
        public void registerListener(IOnNewBookArrivedListener listener) throws RemoteException {
            if (!mListenerList.contains(listener)) {
                mListenerList.add(listener);
            } else {
                Log.d(TAG, "listener already exists " + listener);
            }
        }

        @Override
        public void unregisterListener(IOnNewBookArrivedListener) throws RemoteException {
            if (mListenerList.contains(listener)) {
                mListenerList.remove(listener);
                Log.d(TAG, "unregister listener succeed.");
            } else {
                Log.d(TAG, "listener not found, unregiser failed");
            }
        }
    };

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    @Override
    public void onCreate() {
        super.onCreate();

        mBookList.add(new Book(1, "Think in Java"));
        mBookList.add(new Book(2, "Android Programming"));
        new Thread(new ServiceWorker).start();
    }

    @Override
    public void onDestroy() {
        mIsServiceDestroyed.set(true);
        super.onDestroy();
    }

    private void onNewBookArrived(Book book) throws RemoteException {
        mBookList.add(book);
        // 通知所有Listener
        Log.d(TAG, "new book arrived, notify all listeners");
        for (IOnNewBookArrivedListener listener : mListenerList) {
            listener.onNewBookArrived(book);
        }
    }

    private class ServiceWorker implements Runnable {
        @Override
        public void run() {
            // 每5s在后台生成一本新书
            while(!mIsServiceDestroyed.get()) {
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                int bookId = mBookList.size() + 1;
                Book newBook = new Book(bookId, "new book#" + bookId);
                try {
                    onNewBookArrived(newBook);
                } catch (RemoteExcption e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

BookManagerServicce 置于独立进程中:


客户端 BookManagerActivity

public class BookManagerActivity extends Activity {

    private static final String TAG = "BookManagerActivity";
    private static final int MSG_NEW_BOOK_ARRIVED = 1;

    private IBookManager mRemoteBookManager;

    private ServiceConnection mConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            IBookManager bookManager = IBookManager.Stub.asInterface(service);
            mRemoteBookManager = bookManager;
            try {
                // 服务端的 getBookList() 方法可能会比较耗时,所以需要酌情考虑是否在子线程中进行访问
                List bookList = bookManager.getBookList();
                Log.i(TAG, "book list type: " + bookList.getClass().getCanonicalName());
                Log.i(TAG, "query book list: " + bookList);

                bookManager.registerListener(mOnNewBookArrivedListener);
            } catch(RemoteException e) {
                e.printStackTrace();
            }
        }

        public void onServiceDisconnected(ComponentName name) {
          mRemoteBookManager = null;
        }
    };

    private Handler mHandler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_NEW_BOOK_ARRIVED:
                    String message = "received new book: " + msg.obj;
                    Log.d(TAG, message);
                    break;
            }
            return true;
        }
    });

    private IOnNewBookArrivedListener mOnNewBookArrivedListener = new IOnNewBookArrivedListener.Stub() {
        @Override
        public void onNewBookArrived(Book newBook) throws RemoteException {
            mHandler.obtainMessage(MSG_NEW_BOOK_ARRIVED, newBook).sendToTarget();
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_book_manager);

        Intent intent = new Intent(this, BookManagerService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onDestroy() {
        preDestroy();
        super.onDestroy();
    }

    private void preDestroy() {
        // unregister listener
        if (mRemoteBookManager != null && mRemoteManager.asBinder().isBinderAlive()) {
            try {
                Log.i(TAG, "unregister listener: " + mOnNewBookArrivedListener);
                mRemoteBookManager.unregisterListener(mOnNewBookArrivedListener);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }
        // unbind service
        unbindService(mConnection);
    }
}

log日志:

com.github.tianma8023.ipclearn:remote I/BMS: new book arrived, notify all listeners
com.github.tianma8023.ipclearn D/BookManagerActivity: received new book: Book{bookId=3, bookName='new book#3'}

com.github.tianma8023.ipclearn I/BookManagerActivity: unregister listener: com.github.tianma8023.ipclearn.aidl.BookManagerActivity$4@80e21c1
com.github.tianma8023.ipclearn:remote D/BMS: listener not found, unregister failed

通过日志,可以看出,服务端每次的书籍推送确实收到,但是在服务端执行 unregisterListener 的时候却并没有正确执行。问题的原因在于, Binder 会把客户端传递过来的对象重新转化成新的对象,在客户端注册/反注册过程中使用的是同一个客户端对象,但是通过 Binder 传递到服务端的对象则不一样,所以会存在反注册失败的现象。

上述问题的解决方案就是使用 RemoteCallbackListRemoteCallbackList 由系统提供,专门用来删除跨进成的 listener 接口。

public class RemoteCallbackList

public interface IOnNewBookArrivedListener extends android.os.IInterface

可以看出来,RemoteCallbackList 是一个泛型,可以管理任意的 AIDL 接口。

RemoteCallbackList 部分源码:

public class RemoteCallbackList {
    ArrayMap mCallbacks = new ArrayMap();

    private final class Callback implements IBinder.DeathRecipent {
        final E mCallback;
        final Object mCookie;
        Callback(E callback, Object cookie) {
            mCallback = callback;
            mCookie = cookie;
        }
        // 省略...
    }
}

可以看出来 RemoteCallbackList 内部其实是一个 Map,建立起 IBinderCallback 的映射,而 Callback 又封装了真正的 IInterfacelistener,也就是实际上建立起了 IBinderlistener 的映射。

虽然之前的 IOnNewBookArrivedListener 会由客户端的一个对象会在服务端生成不一样的对象,但是其底层的 Binder 是一样的,所以 RemoteCallbackListener 正是利用了这个特性,真正地实现反注册。

正确姿势:
RemoteCallbackList 替换前面的 CopyOnWriteArrayList

// private CopyOnWiteArrayList mListenerList = new CopyOnWriteArrayList<>();
private RemoteCallbackList mListenerList = new RemoteCallbackList<>();

修改 registerListenerunregisterListener

@Override
public void registerListener(IOnNewBookArrivedListener listener) throws RemoteException {
    mListenerList.register(listener);
}

@Override
public void unregisterListener(IOnNewBookArrivedListener listener) throws RemoteException {
    mListenerList.unregister(listener);
}

修改通知所有已注册的 listener 的 onNewBookArrived 方法:

private void onNewBookArrived(Book book) throws RemoteException {
    mBookList.add(book);
    // 通知所有listener
    Log.i(TAG, "new book arrived, notify all listeners");
    final int N = mListenerList.beginBroadcast();
    for (int i = 0; i < N; i++) {
        IOnNewBookArrivedListener listener = mListenerList.getBroadcastItem(i);
        if(listener != null) {
            listener.onNewBookArrived(book);
        }
    }
    mListenerList.finishBroadcast();
}

注意,遍历 RemoteCallbackList 必须要用上述方式进行,即 begiinBroadcastfinishBroadcast 必须配对使用。

AIDL 重连 Service

当服务端程序意外停止时,Binder 会意外死亡,需要重新连接 Service,有两种解决方案:

  1. Binder 设置 DeathRecipient 监听,当 Binder 死亡时,会回调 DeathRecipient#binderDied(),这时可以重连 Service;
  2. ServiceConnection#onServiceDisconnected() 中重连 Service。

两者的区别在于在 bindDied 中是在客户端的 Binder 线程池被调用,而 onServiceDisconnected 是在UI线程中被回调。

BookManagerActivity 中加入:

public class BookManagerActivity extends Activity {
    // ...
    private IBookManager mRemoteBookManager;

    private IBinder.DeathRecipient mDeathRecipient = new IBinder.DeathRecipient() {
        @Override
        public void binderDied() {
          // 子线程,binder线程
            if (mRemoteBookManager == null) 
                return;
            mRemoteBookManager.asBinder().unlinkToDeath(mDeathRecipient, 0);
            mRemoteBookManager = null;
            // TODO: 重新绑定 Service
        }
    }

    private ServiceConnection mConnection = new ServiceConnection() {
      @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            IBookManager bookManager = IBookManager.Stub.asInterface(service);
            mRemoteBookManager = bookManager;
            try {
                mRemoteBookManager.asBinder().linkToDeath(mDeathRecipient, 0); 
                // ... 省略
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            mRemoteBookManager = null;
            // 主线程
            // TODO: 重连 Service
        }
    }
}

权限验证

默认情况下,远程服务可以被其他外部组件连接上,所以,必要的时候需要加入权限验证。通常有以下几种方案:

  1. 在远程 Service 的 onBind 中进行验证,这里的验证方式也有很多,常用的是使用 permission 进行验证:
    在 AndroidManifest 中声明所需要的权限:
    
    
    BookManagerServiceonBind 中做权限验证:
    public IBinder onBind(Intent intent) {
       // 权限验证
       int result = checkCallingOrSelfPermission (com.github.tianma8023.ipclearn.permission.ACCESS_BOOK_SERVICE);
       if (result == PackageManager.PERMISSION_DENIED)
           return null;
       return mBinder;
    }
    
    这样就完成了权限的验证,当有客户端需要连接该服务时,需要申请权限:
    
    
  2. 在服务端的 Binder#onTransact() 中进行权限验证:
private Binder mBinder = new IBookManager.Stub() {
  // ...
  @Override
  public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
      // 权限验证
      // 1. 需要声明自定权限 "com.github.tianma8023.ipclearn.permission.ACCESS_BOOK_SERVICE"
      // 2. 包名前缀必须是 "com.github.tianma8023"
      int check = checkCallingOrSelfPermission("com.github.tianma8023.ipclearn.permission.ACCESS_BOOK_SERVICE");
      if (check == PackageManager.PERMISSION_DENIED)
          return false;
      String packageName = null;
      String[] packages = getPackageManager().getPackagesForUid(getCallingUid());
      if (packages != null && packages.length > 0) {
          packageName = packages[0];
      }
      if (packageName == null || !packageName.startsWith("com.github.tianma8023")) {
          return false;
      }
      return super.onTransact(code, data, reply, flags);
  }
}

上述代码片段,验证了 permission,还验证了包名前缀,只有都满足要求的才能验证通过。

  1. Service 指定 android:permission 属性。

代码参考

IPCLearn

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