在开发应用的时候，我们有时候需要Service来处理后台任务。同时需要两者之间的实时交互，比如说下载的时候我们需要实时地更新Notification的下载进度。我们可以通过BroadcastReceiver来实现Service和Activity的交互，但是今天我们来介绍另外一种实现方法。使用Handler实现Activity和Service之间的交互。
实现的原理：
1.在Service中的onCreate方法中创建Service端的Handler和Messenger对象，并且在handleMessage方法中获取Activity端的Messenger
2.在Service的onBind方法中返回Messenger的Binder对象
3.在Activity中创建一个Handler对象，用来处理消息
4.在Activity中创建一个ServiceConnection对象，并且在onServiceConnected方法中，获取Service端的Messenger对象
5.在Activity创建Messenger，并封装在Message中传递给Service端
文字不理解可以看图并结合代码来思考
原理图
public class MessengerService extends Service{
private Messenger mActivityMessenger;
private Handler handler;
private Messenger mServiceMessenger;
@Override
public void onCreate() {
super.onCreate();
Log.i("TAG", "onCreate()");
/**
* HandlerThread是Android系统专门为Handler封装的一个线程类，
通过HandlerThread创建的Hanlder便可以进行耗时操作了
* HandlerThread是一个子线程,在调用handlerThread.getLooper()之前必须先执行
* HandlerThread的start方法。
*/
HandlerThread handlerThread = new HandlerThread("serviceCalculate");
handlerThread.start();
handler = new Handler(handlerThread.getLooper()){
@Override
public void handleMessage(Message msg) {
if(msg.what == 0x11){
if(mActivityMessenger == null) {
mActivityMessenger = msg.replyTo;
}
//模拟耗时任务
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//发送结果回Activity
Message message = this.obtainMessage();
message.what = 0x12;
message.arg1 = msg.arg1 + msg.arg2;
try {
mActivityMessenger.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
};
mServiceMessenger = new Messenger(handler);
}
@Override
public IBinder onBind(Intent intent) {
Log.i("TAG","onBind()");
return mServiceMessenger.getBinder();
}
}
public class ScrollingActivity extends AppCompatActivity {
private Button sendToServiceBtn;
//Service端的Messenger对象
private Messenger mServiceMessenger;
//Activity端的Messenger对象
private Messenger mActivityMessenger;
/**
* Activity端的Handler处理Service中的消息
*/
private Handler handler = new Handler(){
@Override
public void handleMessage(Message msg) {
if(msg.what == 0x12){
Toast.makeText(ScrollingActivity.this, "Service发送过来的结果是......"
+ msg.arg1,Toast.LENGTH_SHORT).show();
}
}
};
/**
* Service绑定状态的监听
*/
private ServiceConnection connection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
//获取Service端的Messenger
mServiceMessenger = new Messenger(service);
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_scrolling);
sendToServiceBtn = (Button) findViewById(R.id.btn_sendToService);
sendToServiceBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//Activity端的Messenger
if(mActivityMessenger == null) {
mActivityMessenger = new Messenger(handler);
}
//创建消息
Message message = Message.obtain();
message.what = 0x11;
message.arg1 = 2016;
message.arg2 = 1;
//设定消息要回应的Messenger
message.replyTo = mActivityMessenger;
try {
//通过ServiceMessenger将消息发送到Service中的Handler
mServiceMessenger.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
});
//绑定Service
Intent intent = new Intent(ScrollingActivity.this, MessengerService.class);
bindService(intent, connection, Service.BIND_AUTO_CREATE);
}
}
接下来几篇文章会介绍Message MessageQueue Looper Handler的流程和源代码
