Service启动流程及生命周期

service启动流程

======== case 1. bind a service ============
TestAidl-Client: ------ =====> bindService()------
TestAidl-Client: ------ <===== bindService()------
TestAidl-Service: ------ service onCreate()------
TestAidl-Service: ------ service onBind()------ ：onBind() is only called once, even we call bindService() multiple times, onBind() wont't be invoked.
TestAidl-Client: ------ onServiceConnected()------

======== case 2. unbind a service ============
TestAidl-Client: ------ =====> unbindService()------：if unbindService() is called with an un-bound service, exception will occur : java.lang.IllegalArgumentException: Service not registered
TestAidl-Client: ------ <===== unbindService()------：NOTE: onServiceDisconnected() won't be called due to unbindService(), 只有当servie异常退出时，系统才会调用onServiceDisconnected()
TestAidl-Service: ------ service onUnbind()------：onUnbind() is only called once when the last bound component unbind from the service, usually the service onDestroy() will be called afterwards..
【TestAidl-Service: ------ service onDestroy()------】

======== case 3. start a service ============ 
TestAidl-Client: ------ =====> startService()------
TestAidl-Client: ------ <===== startService()------
TestAidl-Service: ------ service onCreate()------
TestAidl-Client: ------ service onStartCommand()------：You should never call onStartCommand() directly.

======== case 4. stop a service ============ 
TestAidl-Client: ------ =====> stopService()------：stopService() can be called multiple times, nothing happened.
TestAidl-Client: ------ <===== stopService()------
【TestAidl-Service: ------ service onDestroy()------】

所以，在Service，只有onStart( )可被多次调用（通过多次startService调用），其他onCreate( )，onBind( )，onUnbind( )，onDestory( )在一个生命周期中只能被调用一次。

service的生命周期

1. A Started service will be destroyed once stopService() is called, no matter which component calls.

2. A bound service will be destroyed only when the last bound component calls the unbindService().

3. if a service is both started and bound, it will be destroyed when stopService() is called and no one is bound to the service at that time，除此之外，不管是调用unbindService()或者stopService()都是不起作用的。