Activity 与 Service 之间的消息传递

BgService代码

public class BgService extends Service {
    public static final String TAG = "BgService";
    private BgBinder binder;
 
    @Override
    public void onCreate() {
        super.onCreate();
        binder = new BgBinder();
        Log.d(TAG, "onCreate() executed");
    }
 
    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy() executed");
    }
 
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand() executed");
        return super.onStartCommand(intent, flags, startId);
    }
 
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.d(TAG, "onBind() executed");
        return binder;
    }
 
    class BgBinder extends Binder {
        public void doWork() {
            Log.d(TAG, "doWork() executed");
        }
    }
}

Activity 代码

public class MyActivity extends AppCompatActivity {
    private ServiceConnection bgServiceConnection;
    private BgService.BgBinder bgBinder;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...
        bgServiceConnection = new ServiceConnection() {
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                bgBinder = (BgService.BgBinder)service;
                bgBinder.doWork(); // 异步回调必须在这里调用
                Log.d("MyActivity", "onServiceConnected");
            }
 
            @Override
            public void onServiceDisconnected(ComponentName name) {
                bgBinder = null;
                Log.d("MyActivity", "onServiceDisconnected");
            }
        };
        ...
    }
 
    public void startBg(View view) {
        Intent intent = new Intent(this, BgService.class);
        startService(intent);
    }
 
    public void stopBg(View view) {
        Intent intent = new Intent(this, BgService.class);
        stopService(intent);
    }
 
    public void bindBg(View view) {
        Intent intent = new Intent(this, BgService.class);
        bindService(intent, bgServiceConnection, BIND_AUTO_CREATE);
    }
 
    public void unbindBg(View view) {
        unbindService(bgServiceConnection);
    }
}

其中
startService 调用onStartCommand, 如果service未create, 会在调用之前, 调用onCreate
stopService 会检查service被引用的情况, 如果没有其他引用, 则调用onDestroy

bindService 会调用onBind(之后在异步返回中执行onServiceConnected), 如果service未create, 会在调用之前, 调用onCreate. 注意, 不会调用onStartCommand
unbindService 会检查service被引用的情况, 如果没有其他引用, 则调用onDestroy,

unbindService与stopService的区别: stopService可多次调用, 不会抛异常, unbindService在执行后如果再调用会抛异常, 不处理则应用崩溃

onServiceDisconnected为什么没被调用? 这个只有在service因异常而断开连接的时候，这个方法才会被调用 This is called when the connection with the service has been unexpectedly disconnected -- that is, its process crashed. Because it is running in our same process, we should never see this happen.