前言:听说iOS13 把私有的key給禁止了(例如_placeholderLabel),乱调会崩溃,我去,当时我就想..........

好了进入正题,之前用kvc给UITextView添加占位文字挺方便的 就是自己在扩展中通过runtime定义2个属性,自己创建一个label,最后通过kvc给_placeholderLabel就完事了,啥都不要我们操心

Swift版在这
OC版在这

那本文就不用kvc了设置了,那么占位文字的显示隐藏就需要自己控制了,咱们通过观察者来实现占位文字的显示隐藏,真是操碎了心

直接上代码了

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

    /// 占位文字y值调整
    @IBInspectable public var placeholderY: CGFloat {
        get {
            return placeholderLabel.frame.origin.y
        }
        set {
            self.placeholderLabel.frame = CGRect(x: placeholderLabel.frame.origin.x, y: newValue, width: placeholderLabel.frame.size.width, height: placeholderLabel.frame.size.height)
            self.setNeedsLayout()
        }
    }
    /// 占位文字
    @IBInspectable public var placeholder: String {
        get {
            return self.placeholderLabel.text ?? ""
        }
        set {
            let attributedText = NSMutableAttributedString(string: newValue)
            let style = NSMutableParagraphStyle()
            style.lineSpacing = 3 // 别问为啥是3 我也不知道看着像而已
            style.lineBreakMode = .byCharWrapping
            attributedText.addAttribute(.paragraphStyle, value: style, range: NSMakeRange(0,newValue.count))
            placeholderLabel.attributedText = attributedText
        }
    }
    /// 占位文字颜色
    @IBInspectable public var placeholderColor: UIColor {
        get {
            return placeholderLabel.textColor
        }
        set {
            placeholderLabel.textColor = newValue
        }
    }
    
    private var placeholderLabel: UITextViewPlaceholderLabel {
        get {
            var label = objc_getAssociatedObject(self, UITextView.RuntimeKey.hw_placeholderLabelKey!) as? UITextViewPlaceholderLabel
            if label == nil { // 不存在是 创建 绑定
                if (font == nil) { // 防止没大小时显示异常 系统默认设置14
                    font = UIFont.systemFont(ofSize: 14)
                }
                let width = bounds.width-10
                let y: CGFloat = 8
                let x: CGFloat = 6
                let frame = CGRect(x: x, y: y, width: width, height: bounds.size.height-y*2) // 别问为啥是这些数字 看着位置对然后就这样了
                label = UITextViewPlaceholderLabel.init(frame: frame)
                label?.numberOfLines = 0
                label?.font = font
                label?.textColor = UIColor.lightGray
                self.addSubview(label!)
//                self.setValue(label!, forKey: "_placeholderLabel") // 听说iOS13 会崩溃
                addObserver() // 在此添加观察者 保证只添加一次
                objc_setAssociatedObject(self, UITextView.RuntimeKey.hw_placeholderLabelKey!, label!, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
                self.sendSubviewToBack(label!)
            }
            return label!
        }
        set {
            objc_setAssociatedObject(self, UITextView.RuntimeKey.hw_placeholderLabelKey!, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    /// 添加观察者监听内容改变
    private func addObserver() {
        #if swift(>=4.2)
        let UITextViewTextDidChange = UITextView.textDidChangeNotification
        #else
        let UITextViewTextDidChange = Notification.Name.UITextViewTextDidChange
        #endif
        NotificationCenter.default.addObserver(self, selector: #selector(refreshPlaceholder), name:UITextViewTextDidChange, object: self)
    }
    
    @objc internal func refreshPlaceholder() {
        if !text.isEmpty || !attributedText.string.isEmpty {
            placeholderLabel.alpha = 0
        } else {
            placeholderLabel.alpha = 1
        }
    }
  
    open override func removeFromSuperview() {
        super.removeFromSuperview()
        placeholderLabel.removeFromSuperview() // 移除占位Label
        NotificationCenter.default.removeObserver(self) // 移除观察者
    }
}

// MARK: - 调整文字内容在左上角
class UITextViewPlaceholderLabel: UILabel {
    override func textRect(forBounds bounds: CGRect, limitedToNumberOfLines numberOfLines: Int) -> CGRect {
        var textRect = super.textRect(forBounds: bounds, limitedToNumberOfLines: numberOfLines)
        textRect.origin.y = bounds.origin.y
        return textRect
    }
    override func drawText(in rect: CGRect) {
        let actualRect = textRect(forBounds: rect, limitedToNumberOfLines: numberOfLines)
        super.drawText(in: actualRect)
    }
}

出现问题:文字大小导致换行,默认位置不满足必须手动设置(图中第三个编辑框为手动设置补正)

文字大小导致换行,默认位置不满足必须手动设置

image.png

Dome
欢迎大家一起发现问题探讨解决