ActivityMessenger | ActivityMessenger，借助Kotlin特性，简化Activity之间传参和回调的逻辑代码。

I haven't tried this in practice, but it seems reasonable to set mBound = true already when calling bindService instead of in the callback. Actually, the documentation says that you should call unbindService even if bindService returned false (meaning you would never get any onServiceConnected call and mBound would never be true):

Note: If the method returns false, your client does not have a valid connection to the service. However, your client should still call unbindService(); otherwise, your client will keep the service from shutting down when it is idle.

With this in mind it's clear that only setting mBound = true in onServiceConnected is not sufficient (or at least recommended). I would suspect that calling unbindService when not previously bound is a no-op, but that might need some confirmation. If so, setting mBound = true when calling bindService seems like a good approach.