Activity与Service的交互相关的面试题及答案

以下是Activity与Service的交互相关的面试题及答案：

1. Activity如何启动Service？

答：Activity可以通过调用`startService()`方法来启动Service。例如：

Intent intent = new Intent(this, MyService.class);
startService(intent);

2. Service如何与Activity进行通信？

答：Service可以通过Binder机制与Activity进行通信。以下是一些实现方式：

- Service中定义Binder

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

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

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

    public int getRandomNumber() {
        return new Random().nextInt(100);
    }
}

- Activity中绑定Service，并获取Service实例

private MyService mService;
private boolean mBound = false;

private ServiceConnection mConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName className, IBinder service) {
        MyService.MyBinder binder = (MyService.MyBinder) service;
        mService = binder.getService();
        mBound = true;
    }

    @Override
    public void onServiceDisconnected(ComponentName arg0) {
        mBound = false;
    }
};

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

@Override
protected void onStop() {
    super.onStop();
    if (mBound) {
        unbindService(mConnection);
        mBound = false;
    }
}

public void onClick(View view) {
    if (mBound) {
        int num = mService.getRandomNumber();
        Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();
    }
}

3. Service如何在后台执行任务并向Activity发送结果？

答：Service可以通过Handler机制向Activity发送结果。以下是一个例子：

- Service中定义Handler

public class MyService extends Service {
    private Looper mServiceLooper;
    private ServiceHandler mServiceHandler;

    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            // 执行任务
            int result = doWork();

            // 发送结果
            Message message = mHandler.obtainMessage();
            message.arg1 = result;
            mHandler.sendMessage(message);
        }
    }

    @Override
    public void onCreate() {
        super.onCreate();
        HandlerThread thread = new HandlerThread("ServiceStartArguments", Process.THREAD_PRIORITY_BACKGROUND);
        thread.start();

        // 获取Handler的Looper
        mServiceLooper = thread.getLooper();
        // 创建ServiceHandler
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Message message = mServiceHandler.obtainMessage();
        message.arg1 = startId;
        mServiceHandler.sendMessage(message);

        // Service执行完任务后自动停止
        return START_NOT_STICKY;
    }

    private int doWork() {
        // 执行任务
        return new Random().nextInt(100);
    }

    // Activity中定义Handler
    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            Toast.makeText(getApplicationContext(), "Result: " + msg.arg1, Toast.LENGTH_SHORT).show();
        }
    };

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

- Activity中调用Service

Intent intent = new Intent(this, MyService.class);
startService(intent);

通过以上的例子可以看出，Service可以在后台执行任务，并通过Handler机制将结果发送给Activity。