Android组件通讯之Service的基础绑定

当一个Activity通过Intent绑定一个Service时，会调用Service的onBind方法。此方法会返回一个IBinder对象，此对象作为参数传递给Activity中定义好的ServiceConnection中的onServiceConnected()方法，使得Activity获取到Service的操作接口

下面是一个例子，通过两个按钮来绑定和解绑一个Service，但是需要注意的是，如果当前没有绑定Service而直接解绑，会出现IllegalArgumentException，所以比较好的解决办法是使用一个标记接口判断绑定对象是否存在，具体见代码

标记接口:

//  我只是一个空接口
public interface IService {}

然后是我们自己的Service类：

public class MyService extends Service {
    
    private MyBinder myBinder = new MyBinder();
    
    @Override
    public IBinder onBind(Intent intent) {
System.out.println("**** onBind() ****");
        return myBinder;
    }
    
    @Override
    public void onCreate() {
System.out.println("**** onCreate() ****");
        super.onCreate();
    }

    @Override
    public void onDestroy() {
System.out.println("**** onDestroy() ****");
        super.onDestroy();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
System.out.println("**** onStartCommand() ****");
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onRebind(Intent intent) {
System.out.println("**** onRebind() ****");
        super.onRebind(intent);
    }

    @Override
    public boolean onUnbind(Intent intent) {
System.out.println("**** onUnbind() ****");
        return super.onUnbind(intent);
    }
    
    // 注意！ MyBinder为Binder与IService的共同子类
    class MyBinder extends Binder implements IService {}
    
}

Activity：

public class MainActivity extends Activity {
    
    private Button bindServiceBtn = null;
    private Button unbindServiceBtn = null;
    private IService myService = null;
    
    // 实例化ServiceConnection接口用以处理绑定后Service传回的操作接口
    private ServiceConnection conn = new ServiceConnection() {
        
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            System.out.println("**** conn.onServiceConnected() ****");    
            // 此处实际上是参数service向下转型为MyBinder, 然后再向上转型为IService,若绑定成功,则IService对象不为空
            myService = (MyBinder) service;
        }
        
        @Override
        public void onServiceDisconnected(ComponentName name) {
            System.out.println("**** conn.onServiceDisconnected() ****");    
        }
        
    };
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        bindServiceBtn = (Button) findViewById(R.id.bindServiceBtn);
        unbindServiceBtn = (Button) findViewById(R.id.unbindServiceBtn);
        
        bindServiceBtn.setOnClickListener(new BindServiceListener());
        unbindServiceBtn.setOnClickListener(new UnbindServiceListener());
        
    }
    
    private class BindServiceListener implements OnClickListener {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, MyService.class);
            MainActivity.this.bindService(intent, conn, Context.BIND_AUTO_CREATE);
        }
    }
    
    private class UnbindServiceListener implements OnClickListener {
        @Override
        public void onClick(View v) {
            // 判断IService是否为空,不为空才可解绑
            if (MainActivity.this.myService != null) {
                MainActivity.this.unbindService(conn);
                MainActivity.this.myService = null;
            } else {
                Toast.makeText(MainActivity.this, "请绑定服务", Toast.LENGTH_SHORT).show();
            }
        }
    }

}