在Activity中獲取Service對象可以通過以下步驟：

1. 在Activity中使用bindService()方法綁定Service。在onServiceConnected()方法中獲取Service對象。

public class MyActivity extends Activity {
    private MyService myService;

    private ServiceConnection serviceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            MyService.MyBinder binder = (MyService.MyBinder) service;
            myService = binder.getService();
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            myService = null;
        }
    };

    @Override
    protected void onStart() {
        super.onStart();
        Intent serviceIntent = new Intent(this, MyService.class);
        bindService(serviceIntent, serviceConnection, Context.BIND_AUTO_CREATE);
    }

    @Override
    protected void onStop() {
        super.onStop();
        unbindService(serviceConnection);
    }
}

2. 在Service中創建一個Binder類用于返回Service對象。

public class MyService extends Service {
    private final IBinder binder = new MyBinder();

    public class MyBinder extends Binder {
        MyService getService() {
            return MyService.this;
        }
    }

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

通過這樣的方式，可以在Activity中獲取到Service對象并調用其方法。