Show emoji keyboard first time when user touched UITextView.


Keypoint is ‘textInputMode’ in UITextView. 

class EmojiTextView: UITextView {
    override var textInputMode: UITextInputMode? {
        for mode in UITextInputMode.activeInputModes {
            if mode.primaryLanguage == "emoji" {
                return mode
            }
        }
        return self.textInputMode
    }
}