UITextView+maxLengthAndPlaceHolder.swift

private var __maxLengthsForTextView = [UITextView: Int]()
private var kAssociationKeyMaxLengthTextView: Int = 0

extension UITextView:UITextViewDelegate {
    @IBInspectable var maxLength: Int {
        get {
            if let length = objc_getAssociatedObject(self, &kAssociationKeyMaxLengthTextView) as? Int {
                return length
            } else {
                return Int.max
            }
        }
        set {
            self.delegate = self
            
            objc_setAssociatedObject(self, &kAssociationKeyMaxLengthTextView, newValue, .OBJC_ASSOCIATION_RETAIN)
        }
    }
    
    /*public func textViewDidChange(_ textView: UITextView) {
        checkMaxLength(textField: self)
    }*/
    @objc func checkMaxLength(textField: UITextView) {
        guard let prospectiveText = self.text,
            prospectiveText.count > maxLength
            else {
                return
        }
        
        let selection = selectedTextRange
        
        let indexEndOfText = prospectiveText.index(prospectiveText.startIndex, offsetBy: maxLength)
        let substring = prospectiveText[..<indexEndOfText]
        text = String(substring)
        
        selectedTextRange = selection
    }
    
    
    /// Resize the placeholder when the UITextView bounds change
    override open var bounds: CGRect {
        didSet {
            self.resizePlaceholder()
        }
    }
    
    /// The UITextView placeholder text
    public var placeholder: String? {
        get {
            var placeholderText: String?
            
            if let placeholderLabel = self.viewWithTag(100) as? UILabel {
                placeholderText = placeholderLabel.text
            }
            
            return placeholderText
        }
        set {
            if let placeholderLabel = self.viewWithTag(100) as! UILabel? {
                placeholderLabel.text = newValue
                placeholderLabel.sizeToFit()
            } else {
                self.addPlaceholder(newValue!)
            }
        }
    }
    
    /// When the UITextView did change, show or hide the label based on if the UITextView is empty or not
    ///
    /// - Parameter textView: The UITextView that got updated
    public func textViewDidChange(_ textView: UITextView) {
        if let placeholderLabel = self.viewWithTag(100) as? UILabel {
            placeholderLabel.isHidden = self.text.count > 0
        }
        checkMaxLength(textField: self)
    }
    
    func checkPlaceholder() {
        if let placeholderLabel = self.viewWithTag(100) as? UILabel {
            placeholderLabel.isHidden = self.text.count > 0
        }
        checkMaxLength(textField: self)
    }
    
    /// Resize the placeholder UILabel to make sure it's in the same position as the UITextView text
    private func resizePlaceholder() {
        if let placeholderLabel = self.viewWithTag(100) as! UILabel? {
            let labelX = self.textContainer.lineFragmentPadding
            let labelY = self.textContainerInset.top - 2
            let labelWidth = self.frame.width - (labelX * 2)
            let labelHeight = placeholderLabel.frame.height

            placeholderLabel.frame = CGRect(x: labelX, y: labelY, width: labelWidth, height: labelHeight)
        }
    }
    
    /// Adds a placeholder UILabel to this UITextView
    private func addPlaceholder(_ placeholderText: String) {
        let placeholderLabel = UILabel()
        
        placeholderLabel.text = placeholderText
        placeholderLabel.sizeToFit()
        
        placeholderLabel.font = self.font
        placeholderLabel.textColor = UIColor.lightGray
        placeholderLabel.tag = 100
        
        placeholderLabel.isHidden = self.text.count > 0
        
        self.addSubview(placeholderLabel)
        self.resizePlaceholder()
        self.delegate = self
    }
}