Every time when the app opens fire $ionicPush.register?

I was trying to read a notification using $rootScope.$on(’$cordovaPush:notificationReceived’, function(event, notification). It only works for the first time app opening. Then whenever the app is reopened it doesn’t work.

Is it a good practice to call $ionicPush.register? every time the app opens?
Or any other way I can get $cordovaPush:notificationReceived fired.