使用案例

extension UITextView {
    private struct RuntimeKey {
        static let hw_placeholderLabelKey = UnsafeRawPointer.init(bitPattern: "hw_placeholderLabelKey".hashValue)
        /// ...其他Key聲明
    }

    /// 占位文字
    @IBInspectable public var placeholder: String {
        get {
            return self.placeholderLabel.text ?? ""
        }
        set {
            self.placeholderLabel.text = newValue
        }
    }

    /// 占位文字顏色
    @IBInspectable public var placeholderColor: UIColor {
        get {
            return self.placeholderLabel.textColor
        }
        set {
            self.placeholderLabel.textColor = newValue
        }
    }

    private var placeholderLabel: UILabel {
        get {
            var label = objc_getAssociatedObject(self, UITextView.RuntimeKey.hw_placeholderLabelKey!) as? UILabel
            if label == nil {
                if (self.font == nil) {
                    self.font = UIFont.systemFont(ofSize: 14)
                }
                label = UILabel.init(frame: self.bounds)
                label?.numberOfLines = 0
                label?.font = self.font
                label?.textColor = UIColor.lightGray
                self.addSubview(label!)
                self.setValue(label!, forKey: "_placeholderLabel")
                objc_setAssociatedObject(self, UITextView.RuntimeKey.hw_placeholderLabelKey!, label!, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
                self.sendSubview(toBack: label!)
            }
            return label!
        }
        set {
            objc_setAssociatedObject(self, UITextView.RuntimeKey.hw_placeholderLabelKey!, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
}
 

Swift-UITextView占位文字及占位文字顏色擴展(可在xib中直接使用)