深入Android架构(从线程到AIDL)_20 IPC的Proxy-Stub设计模式02

2、 IBinder接口的一般用途

前言

一般用途

Android的IPC框架仰赖单一的IBinder接口。此时Client端调用IBinder接口的transact()函数，透过IPC机制而调用到远方(Remote)的onTransact()函数。
在Java层框架里， IBinder接口实现于Binder基类，如下图：
myActivity调用IBinder接口，执行myBinder的onTransact()函数，可送信息给myService去播放mp3音乐，如下图：
myService也能送Broadcast信息给myActivity，将字符串显示于画面上：

// myActivity.java
// ………
public class myActivity extends Activity implements OnClickListener {private final int WC = LinearLayout.LayoutParams.WRAP_CONTENT;private final int FP = LinearLayout.LayoutParams.FILL_PARENT;private Button btn, btn2, btn3;public TextView tv;private IBinder ib = null;private final String MY_S_EVENT = new String("com.misoo.pk01.myService.MY_S_EVENT");protected final IntentFilter filter=new IntentFilter(MY_S_EVENT);private BroadcastReceiver receiver=new myIntentReceiver();public void onCreate(Bundle icicle) {super.onCreate(icicle);LinearLayout layout = new LinearLayout(this);layout.setOrientation(LinearLayout.VERTICAL);btn = new Button(this); btn.setId(101); btn.setText("play");btn.setBackgroundResource(R.drawable.heart);btn.setOnClickListener(this);LinearLayout.LayoutParams param = new LinearLayout.LayoutParams(80, 50);param.topMargin = 10; layout.addView(btn, param);btn2 = new Button(this);btn2.setId(102);btn2.setText("stop");btn2.setBackgroundResource(R.drawable.heart);btn2.setOnClickListener(this);layout.addView(btn2, param);btn3 = new Button(this);btn3.setId(103); btn3.setText("exit");btn3.setBackgroundResource(R.drawable.cloud);btn3.setOnClickListener(this);layout.addView(btn3, param);tv = new TextView(this); tv.setText("Ready");LinearLayout.LayoutParams param2 = newLinearLayout.LayoutParams(FP, WC);param2.topMargin = 10;layout.addView(tv, param2);setContentView(layout);//---------------------------------registerReceiver(receiver, filter);//------------------------------------------------------bindService( new Intent("com.misoo.pk01.REMOTE_SERVICE"),mConnection, Context.BIND_AUTO_CREATE);}btn3 = new Button(this);btn3.setId(103); btn3.setText("exit");btn3.setBackgroundResource(R.drawable.cloud);btn3.setOnClickListener(this);layout.addView(btn3, param);tv = new TextView(this); tv.setText("Ready");LinearLayout.LayoutParams param2 = newLinearLayout.LayoutParams(FP, WC);param2.topMargin = 10;layout.addView(tv, param2);setContentView(layout);//---------------------------------registerReceiver(receiver, filter);//------------------------------------------------------bindService( new Intent("com.misoo.pk01.REMOTE_SERVICE"),mConnection, Context.BIND_AUTO_CREATE) );
}private ServiceConnection mConnection =new ServiceConnection() {@Override public void onServiceConnected(ComponentName className, IBinder ibinder) {ib = ibinder;}@Override public void onServiceDisconnected(ComponentName name) { }
};public void onClick(View v) {switch (v.getId()) {case 101: // Play ButtonParcel data = Parcel.obtain();Parcel reply = Parcel.obtain();try { ib.transact(1, data, reply, 0);} catch (Exception e) { e.printStackTrace(); }break;case 102: // Stop Buttondata = Parcel.obtain(); reply = Parcel.obtain();try { ib.transact(2, data, reply, 0);} catch (Exception e) { e.printStackTrace(); }break;case 103: finish(); break;}
}

其中的代码：
case 101: // Play Button
        //…..
        ib.transact(1, data, reply, 0);
case 102: // Stop Button
        // …..
        ib.transact(2, data, reply, 0);
就是对<Play>和<Stop>两个功能进行”编码” 的动作。
编好码之后，就将这编码值当做第1个参数传给IBinder接口的transact()函数。
于是编码值就跨进程地传递到myBinder类里的onTransact()函数了。

class myIntentReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {int bn = intent.getIntExtra("key",-1);if(bn == 0)tv.setText("Playing");elsetv.setText("Stop.");}
}// myService.java
// ……..
public class myService extends Service implements Runnable {private IBinder mBinder = null;private Thread th1;public static Handler h;private MediaPlayer mPlayer = null;public static Context ctx;private final String MY_S_EVENT = new String("com.misoo.pk01.myService.MY_S_EVENT");@Override public void onCreate() {super.onCreate(); ctx = this;mBinder = new myBinder();// 诞生一个子线程及其MQ； 等待Messageth1 = new Thread(this);th1.start();}@Overridepublic IBinder onBind(Intent intent) { return mBinder; }public void run() {Looper.prepare();h = new EventHandler(Looper.myLooper());Looper.loop();}//---------------------------------------class EventHandler extends Handler {public EventHandler(Looper looper) { super(looper); }public void handleMessage(Message msg) {String obj = (String)msg.obj;if(obj.contains("play")) {if(mPlayer != null) return;//----------------------------------Intent in = new Intent(MY_S_EVENT);in.putExtra("key", 0);ctx.sendBroadcast(in);//----------------------------------mPlayer = MediaPlayer.create(ctx, R.raw.dreamed);try { mPlayer.start();} catch (Exception e) {Log.e("Play", "error: " + e.getMessage(), e);}}else if(obj.contains("stop")) {if (mPlayer != null) {Intent in = new Intent(MY_S_EVENT);in.putExtra("key", 1);ctx.sendBroadcast(in);//----------------------------------mPlayer.stop(); mPlayer.release();mPlayer = null;}}}}
}// myBinder.java
// …….
public class myBinder extends Binder{@Override public boolean onTransact( int code, Parcel data, Parcel reply, int flags) throws android.os.RemoteException {switch( code ){case 1:// 将Message丢到子线程的MQ to play MP3String obj = "play";Message msg = myService.h.obtainMessage(1,1,1,obj);myService.h.sendMessage(msg);break;case 2:// 将Message丢到子线程的MQ to stop playingobj = "stop";msg = myService.h.obtainMessage(1,1,1,obj);myService.h.sendMessage(msg);break;}return true;}
}