When switch the net network from 5G to 4G in Setting->Cellular->Primary(the current card using for WANN) -> voice & data -> change to 4G.
The iOS API
SCNetworkReachabilitySetCallback
not callback.
I try using CTServiceRadioAccessTechnologyDidChangeNotification to get the notification, but won't work too.
And using addObserver:forKeyPath to observer the CTTelephonyNetworkInfo
instance's
currentRadioAccessTechnology value, it not change too.
But if you create a new CTTelephonyNetworkInfo instance, the currentRadioAccessTechnology will return a new value which is correct.
So it seems the only way to get the new currentRadioAccessTechnology in time， is to start a timer. Is there a graceful way to get it ?