iOS 개발: UITExtView에 자리 표시자를 추가하는 방법

class CustomTextView: UITextView {
    private var _placeholder:String!
    
    init(frame:CGRect,placeholder:String) {
        super.init(frame: frame, textContainer: nil)
        _placeholder = placeholder
        NotificationCenter.default.addObserver(self, selector: #selector(textDidChange), name: .UITextViewTextDidChange, object: self)//         
    }
    
    override func draw(_ rect: CGRect) {
        if hasText{
            return//         ，    
        }
        _placeholder.draw(in: CGRect(x:5,y:7,width:rect.width-10,height:rect.height), withAttributes: [NSForegroundColorAttributeName:UIColor.yellow,NSFontAttributeName:UIFont.systemFont(ofSize: 14)])//        ，            ，                ，     
    }
    
    func textDidChange(){
        setNeedsDisplay()//  drawRect  ，      drawRect  
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}
///////////////////////

    override func viewDidLoad() {
        super.viewDidLoad()
        let textView = CustomTextView(frame: CGRect(x: 100, y: 100, width: 100, height: 100),placeholder:"     ")
        textView.backgroundColor = UIColor.brown
        view.addSubview(textView)
    }