【Swift】UITextViewにPlaceholderを追加する

public class PlaceHolderTextView: UITextView {

    lazy var placeHolderLabel:UILabel = UILabel()
    var placeHolderColor:UIColor      = UIColor.lightGray
    var placeHolder:String          = ""

    required public init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)!
    }

    deinit {
        NotificationCenter.default.removeObserver(self)
    }

    override public func awakeFromNib() {
        super.awakeFromNib()

        NotificationCenter.default.addObserver(self, selector: #selector(textChanged(notification:)), name: UITextView.textDidChangeNotification, object: nil)
    }

    override public func draw(_ rect: CGRect) {
        if(self.placeHolder.count > 0) {
            self.placeHolderLabel.frame           = CGRect(x: 8, y:8, width:self.bounds.size.width - 16,height: 0)
            self.placeHolderLabel.lineBreakMode   = NSLineBreakMode.byWordWrapping
            self.placeHolderLabel.numberOfLines   = 0
            self.placeHolderLabel.font            = self.font
            self.placeHolderLabel.backgroundColor = UIColor.clear
            self.placeHolderLabel.textColor       = self.placeHolderColor
            self.placeHolderLabel.alpha           = 0
            self.placeHolderLabel.tag             = 1

            self.placeHolderLabel.text = self.placeHolder as String
            self.placeHolderLabel.sizeToFit()
            self.addSubview(placeHolderLabel)
        }

        self.sendSubviewToBack(placeHolderLabel)

        if(self.text.utf16.count == 0 && self.placeHolder.count > 0){
            self.viewWithTag(1)?.alpha = 1
        }

        super.draw(rect)
    }

    @objc public func textChanged(notification:NSNotification?) -> (Void) {
        if(self.placeHolder.count == 0){
            return
        }

        if(self.text.utf16.count == 0) {
            self.viewWithTag(1)?.alpha = 1
        }else{
            self.viewWithTag(1)?.alpha = 0
        }
    }

}

var textView = PlaceHolderTextView()
textView.placeHolder = "hogehoge"