BroadcastReceiver的register与unregister的timing问题

http://stackoverflow.com/questions/7887169/android-when-to-register-unregister-broadcast-receivers-created-in-an-activity

onDestroy() is not guaranteed to be called, and you could continue receiving broadcasts for a long time, when the Activity is no longer open.

onDestroy()

并不能保证被调用，所以有这种可能：在

onDestroy()

没有被调用的情况下（此时Activity并不在前台foreground），而你还在接收Broadcast，这可能不是你想要的。

所以，如只想在Activity在前台的时候接收Broadcast，那你就用

onResume() / onPause()