BindService

public class BindService extends Service {
    private int mCount;

    private boolean mQuit;

    // 定义onBinder方法所返回的对象
    private final MyBinder mBinder = new MyBinder();

    // 通过继承Binder来实现IBinder类
    public class MyBinder extends Binder
    {
        public int getCount() {
            // 获取Service的运行状态：count
            return mCount;
        }
    }

    // 必须实现的方法，绑定该Service时回调该方法
    @Override
    public IBinder onBind(Intent intent) {
        System.out.println("Service is Binded");
        // 返回IBinder对象
        return mBinder;
    }

    // Service被创建时回调该方法。
    @Override
    public void onCreate() {
        super.onCreate();
        System.out.println("Service is Created");
        // 启动一条线程、动态地修改count状态值
        new Thread() {
            @Override
            public void run() {
                while (!mQuit) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                    }
                    mCount++;
                }
            }
        }.start();
    }

    // Service被断开连接时回调该方法
    @Override
    public boolean onUnbind(Intent intent) {
        System.out.println("Service is Unbinded");
        return true;
    }

    // Service被关闭之前回调该方法。
    @Override
    public void onDestroy() {
        super.onDestroy();
        this.mQuit = true;
        System.out.println("Service is Destroyed");
    }
}

<!-- 配置该Service组件 -->
<service android:name=".BindService" >
    <intent-filter>
        <action android:name="org.crazyit.service.BIND_SERVICE" />
    </intent-filter>
</service>

public class BindServiceTest extends Activity {
    Button bind, unbind, getServiceStatus;

    // 保持所启动的Service的IBinder对象
    BindService.MyBinder mBinder;

    // 定义一个ServiceConnection对象
    private final ServiceConnection mConnection = new ServiceConnection() {

        @Override
        // 当该Activity与Service连接成功时回调该方法
        public void onServiceConnected(ComponentName name, IBinder service) {
            System.out.println("--Service Connected--");
            // 获取Service的onBind方法所返回的MyBinder对象
            mBinder = (BindService.MyBinder) service;
        }

        @Override
        // 当该Activity与Service断开连接时回调该方法
        public void onServiceDisconnected(ComponentName name) {
            System.out.println("--Service Disconnected--");
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        bind = (Button) findViewById(R.id.bind);
        unbind = (Button) findViewById(R.id.unbind);
        getServiceStatus = (Button) findViewById(R.id.getServiceStatus);

        // 创建启动Service的Intent
        final Intent intent = new Intent();
        intent.setAction("org.crazyit.service.BIND_SERVICE");

        bind.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View source) {
                // 绑定指定Serivce
                bindService(intent, mConnection, Service.BIND_AUTO_CREATE);
            }
        });

        unbind.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View source) {
                // 解除绑定Serivce
                unbindService(mConnection);
            }
        });

        getServiceStatus.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View source) {
                // 获取、并显示Service的count值
                Toast.makeText(BindServiceTest.this, "Serivce的count值为：" + mBinder.getCount(), Toast.LENGTH_SHORT).show();
            }
        });
    }
}

对于servicer的onBind()方法所返回的IBinder对象来说，它可被当成该Service组件所返回的回调对象，service允许客户端通过该IBinder对象来访问Service内部的数据，这样即可实现客户端与Service之间的通信。