Develop系列-API Guides-应用组件-Services-Bound Services

Bound Services

CS架构,其中C是调用组件,S是Bound Services;

C通过bindService来绑定,这个方法立即返回,没有返回值,C需要实现ServiceConnection里面的onServiceConnected和onServiceDisconnected接口。

多个C绑定同一个S时,S只调用一次onBind返回IBinder,后续来绑定S的C,直接得到同一个IBinder,onBind不再重复执行。

创建Bound Services

  • 扩展Binder类:只在应用内部调用的服务,不会被其他应用或者跨进程调用。
  • 使用Messenger:Service定义Handler来接收Message,Client发送Message。这是IPC调用最简单的实现方式,但是Messenger队列在一个线程中排队处理所有请求,没法同时多线程处理。
  • 用AIDL:如果是跨进程的并且需要同时处理多个请求,那么请直接使用AIDL

扩展Binder类

Service代码:

public class LocalService extends Service {

    // Binder given to clients

    private final IBinder mBinder = new LocalBinder();

    // Random number generator

    private final Random mGenerator = new Random();

    /**

     * Class used for the client Binder.  Because we know this service always

     * runs in the same process as its clients, we don't need to deal with IPC.

     */

    public class LocalBinder extends Binder {

        LocalService getService() {

            // Return this instance of LocalService so clients can call public methods

            return LocalService.this;

        }

    }

    @Override

    public IBinder onBind(Intent intent) {

        return mBinder;

    }

    /** method for clients */

    public int getRandomNumber() {

      return mGenerator.nextInt(100);

    }

}

Client代码:

public class BindingActivity extends Activity {

    LocalService mService;

    boolean mBound = false;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

    }

    @Override

    protected void onStart() {

        super.onStart();

        // Bind to LocalService

        Intent intent = new Intent(this, LocalService.class);

        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);

    }

    @Override

    protected void onStop() {

        super.onStop();

        // Unbind from the service

        if (mBound) {

            unbindService(mConnection);

            mBound = false;

        }

    }

    /** Called when a button is clicked (the button in the layout file attaches to

      * this method with the android:onClick attribute) */

    public void onButtonClick(View v) {

        if (mBound) {

            // Call a method from the LocalService.

            // However, if this call were something that might hang, then this request should

            // occur in a separate thread to avoid slowing down the activity performance.

            int num = mService.getRandomNumber();

            Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();

        }

    }



    /** Defines callbacks for service binding, passed to bindService() */

    private ServiceConnection mConnection = new ServiceConnection() {

        @Override

        public void onServiceConnected(ComponentName className,

                IBinder service) {

            // We've bound to LocalService, cast the IBinder and get LocalService instance

            LocalBinder binder = (LocalBinder) service;

            mService = binder.getService();

            mBound = true;

        }

        @Override

        public void onServiceDisconnected(ComponentName arg0) {

            mBound = false;

        }

    };

}

使用Messenger

Service代码:

public class MessengerService extends Service {

    /** Command to the service to display a message */

    static final int MSG_SAY_HELLO = 1;

    /**

     * Handler of incoming messages from clients.

     */

    class IncomingHandler extends Handler {

        @Override

        public void handleMessage(Message msg) {

            switch (msg.what) {

                case MSG_SAY_HELLO:

                    Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show();

                    break;

                default:

                    super.handleMessage(msg);

            }

        }

    }

    /**

     * Target we publish for clients to send messages to IncomingHandler.

     */

    final Messenger mMessenger = new Messenger(new IncomingHandler());

    /**

     * When binding to the service, we return an interface to our messenger

     * for sending messages to the service.

     */

    @Override

    public IBinder onBind(Intent intent) {

        Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show();

        return mMessenger.getBinder();

    }

}

Client代码:

public class ActivityMessenger extends Activity {

    /** Messenger for communicating with the service. */

    Messenger mService = null;

    /** Flag indicating whether we have called bind on the service. */

    boolean mBound;

    /**

     * Class for interacting with the main interface of the service.

     */

    private ServiceConnection mConnection = new ServiceConnection() {

        public void onServiceConnected(ComponentName className, IBinder service) {

            // This is called when the connection with the service has been

            // established, giving us the object we can use to

            // interact with the service.  We are communicating with the

            // service using a Messenger, so here we get a client-side

            // representation of that from the raw IBinder object.

            mService = new Messenger(service);

            mBound = true;

        }

        public void onServiceDisconnected(ComponentName className) {

            // This is called when the connection with the service has been

            // unexpectedly disconnected -- that is, its process crashed.

            mService = null;

            mBound = false;

        }

    };

    public void sayHello(View v) {

        if (!mBound) return;

        // Create and send a message to the service, using a supported 'what' value

        Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0);

        try {

            mService.send(msg);

        } catch (RemoteException e) {

            e.printStackTrace();

        }

    }



    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

    }

    @Override

    protected void onStart() {

        super.onStart();

        // Bind to the service

        bindService(new Intent(this, MessengerService.class), mConnection,

            Context.BIND_AUTO_CREATE);

    }

    @Override

    protected void onStop() {

        super.onStop();

        // Unbind from the service

        if (mBound) {

            unbindService(mConnection);

            mBound = false;

        }

    }

}

绑定服务

只有activities、Services、content providers能绑定到服务,broadcast receiver不能绑定!

生命周期

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