add the observer

gistfile1.txt

func createObservers() {
        NotificationCenter.default.addObserver(self, selector: #selector(TabBarController.setBadge(notification:)), name: addItemNotfication, object: nil)
}

@objc func setBadge(notification: NSNotification) {
        //get the existant badge value
        let badgeValue = Int(self.tabBar.items![0].badgeValue!)!
        // set the new badge value
        self.tabBar.items![0].badgeValue = "\(badgeValue + 1)"
}