iOS - Swift 扩展UITextField属性实现输入长度限制

最近发现使用- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string; // return NO to not change text代理方法进行输入长度控制时，出现在第三方键盘输入表情符号时键盘删除键失效的bug 代码如下：

// 限制 textField 输入长度
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        // 出现第三方键盘输入表情符号时会出现键盘删除键失效的bug
        if textField == name_TF {
            let maxLength = 100
            let currentText = textField.text ?? ""
            guard let stringRange = Range(range, in: currentText) else { return false }
            let updatedText = currentText.replacingCharacters(in: stringRange, with: string)
            return updatedText.count <= maxLength
        }
        return true
    }

不深究只看结果

通过扩展UITextField的lk_maxLength属性，实现输入长度的限制

import UIKit

extension UITextField {
    // 增加扩展属性
    private struct LKTextFieldMaxLengthAssociatedKeys {
        static var maxLength  = 0
    }
    
    @objc var lk_maxLength:Int {
        
        get {
            return objc_getAssociatedObject(self, &LKTextFieldMaxLengthAssociatedKeys.maxLength) as? Int ?? 0
        }
        
        set(newValue) {
            self.addTarget(self, action: #selector(checkMaxLength), for: .editingChanged)
            objc_setAssociatedObject(self, &LKTextFieldMaxLengthAssociatedKeys.maxLength, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
    
    @objc private func checkMaxLength() {
        
        guard let maxLength = objc_getAssociatedObject(self, &LKTextFieldMaxLengthAssociatedKeys.maxLength) as? Int,
              maxLength > 0,
              let prospectiveText = self.text,
              prospectiveText.count > maxLength
        else {
            return
        }
        
        let selection = selectedTextRange
        
        let maxCharIndex = prospectiveText.index(prospectiveText.startIndex, offsetBy: maxLength)
        let newText = String(prospectiveText[..<maxCharIndex])
        
        self.text = newText
        selectedTextRange = selection
    }
}

使用

name_TF.lk_maxLength = 10 // 限制名称长度