iOS12
单独设置每个tabBarItem
vc.tabBarItem.setTitleTextAttributes([NSAttributedString.Key.foregroundColor :UIColor.red ,NSAttributedString.Key.font:UIFont .systemFont(ofSize: 13)], for: .selected)
vc.tabBarItem.setTitleTextAttributes([NSAttributedString.Key.foregroundColor : UIColor.black,NSAttributedString.Key.font:UIFont.systemFont(ofSize: 13)], for: .normal)
iOS13
if #available(iOS 13.0, *){
let standardAppearance = self.tabBar.standardAppearance.copy()
let inlineLayoutAppearance:UITabBarItemAppearance = UITabBarItemAppearance.init()
inlineLayoutAppearance.normal.titleTextAttributes = [NSAttributedString.Key.foregroundColor :normalColor ,NSAttributedString.Key.font:notmalFont]
inlineLayoutAppearance.selected.titleTextAttributes = [NSAttributedString.Key.foregroundColor :selectedColor ,NSAttributedString.Key.font:selectedFont]
standardAppearance.stackedLayoutAppearance = inlineLayoutAppearance
self.tabBar.standardAppearance = standardAppearance
}
注：在iOS13 使用12方法，自改文字大小，造成文字不居中。但是使用iOS13方法修改后，文字显示不全，所以在iOS13 中要两种方法都加上。
