UITextField+MaxTextLength Swift 4

UITextField+MaxTextLength.swift

import UIKit

private var _UITextField_maxTextLength = "_UITextField_maxTextLength"

extension UITextField {
    
    @IBInspectable
    var maxTextLength:Int {
        get {
            return objc_getAssociatedObject(self,
                                            &_UITextField_maxTextLength) as? Int ?? .max
        }
        set {
            if  objc_getAssociatedObject(self, &_UITextField_maxTextLength) != nil {
                objc_setAssociatedObject(self, &_UITextField_maxTextLength,
                                         newValue, .OBJC_ASSOCIATION_ASSIGN)
                return
            }
            addTarget(self, action: #selector(__textChanged), for: .editingChanged)
            objc_setAssociatedObject(self, &_UITextField_maxTextLength,
                                     newValue, .OBJC_ASSOCIATION_ASSIGN)
        }
    }
    
    @objc private func __textChanged() {
        let maxCount = maxTextLength
        if let text = text,
           text.count > maxCount {
            let endIndex = text.index(text.startIndex, offsetBy: maxCount)
            self.text = String(text[..<endIndex])
        }
    }
}