实现效果:

点击进入输入状态时placeholder变小上移,退出输入状态时若是textfield为空则恢复原状.

密码类型有明密文转换按钮.

使用extension实现通过修改属性控制最大输入数,默认15.

#实现思路:
使用自定制的label代替placeholder,在代理中判断textfield当前状态.根据输入状态来修改自定制label的状态.

给textfield加extension,通过runtime为其加最大输入数属性,使其实现方法来控制最大输入数.

实现方式:

1.重写textfield,来实现我们需要的样式.

2.为textfield加拓展,来实现最大输入数控制.

3.实现动画效果.

4.在代理方法中判断状态调用textfield的动画方法

1.重写textfield,来实现我们需要的样式.

  private let bottomLine : CALayer = {
        let line = CALayer()
        line.backgroundColor = UIColor.x4FB0FF.cgColor
        line.isHidden = true
        return line
    }()
    public let label : UILabel = {
        let label = UILabel()
        label.font = UIFont.systemFont(ofSize: 18)
        label.textColor = UIColor.x333333_alpha40
        label.textAlignment = .left
        label.frame = CGRect(x: 0, y: 0, width: 100, height: 30)
        return label
    }()
/// init方法
    ///
    /// - Parameters:
    ///   - frame: frame
    ///   - isSecure: 是否是密码格式
    init(frame:CGRect,isSecure:Bool){
        super.init(frame:frame)
        self.isSecureTextEntry = isSecure
        drawMyView()
        /// 添加字数判断
        addChangeTextTarget()
    }
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func drawMyView()  {
        self.addSubview(label)
        self.layer.addSublayer(bottomLine)
        if self.isSecureTextEntry {
            let passwordSwitch = PassowrdSwitch(frame: CGRect(x: 0, y: 0, width: 21, height: 12.5))
            passwordSwitch.addTarget(self, action: #selector(togglePasswordHidden(sender:)), for: .touchUpInside)
            self.rightView = passwordSwitch
            self.rightViewMode = .always
        }
    }

2.为textfield加拓展,来实现最大输入数控制.

   var maxTextNumberDefault = 15

extension UITextField{
    /// 使用runtime给textField添加最大输入数属性,默认15
    var maxTextNumber: Int {
        set {
            objc_setAssociatedObject(self, &maxTextNumberDefault, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_COPY_NONATOMIC)
        }
        get {
            if let rs = objc_getAssociatedObject(self, &maxTextNumberDefault) as? Int {
                return rs
            }
            return 15
        }
    }
    /// 添加判断数量方法
    func addChangeTextTarget(){
        self.addTarget(self, action: #selector(changeText), for: .editingChanged)
    }
    @objc func changeText(){
        //判断是不是在拼音状态,拼音状态不截取文本
        if let positionRange = self.markedTextRange{
            guard self.position(from: positionRange.start, offset: 0) != nil else {
                checkTextFieldText()
                return
            }
        }else {
            checkTextFieldText()
        }
    }
    /// 判断已输入字数是否超过设置的最大数.如果是则截取
    func checkTextFieldText(){
        guard (self.text?.length)! <= maxTextNumber  else {
            self.text = (self.text?.stringCut(end: maxTextNumber))!
            return
        }
    }
}

3.实现动画效果.

   /// 将placeholder上移方法,点击空的textfield时调用
    public func changeLabel(){
        UIView.animate(withDuration: 0.4) {
            self.label.frame = CGRect(x: 0, y: -20, width: 100, height: 20)
            self.label.font = UIFont.systemFont(ofSize: 10)
            self.label.textColor = UIColor.x4FB0FF
        }
    }
    public func changeLineHidden(){
        self.bottomLine.isHidden = !self.bottomLine.isHidden
    }

    /// placeholder下移方法,当文字清空时调用
    public func disChangeLabel(){
        UIView.animate(withDuration: 0.4) {
            self.label.frame = CGRect(x: 0, y: 0, width: 100, height: self.frame.size.height)
            self.label.font = UIFont.systemFont(ofSize: 18)
            self.label.textColor = UIColor.x333333_alpha40
        }
    }

4.在代理方法中判断状态调用textfield的动画方法

extension ViewController: UITextFieldDelegate{
    func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
        if textField is CRTextField {
            let tf = textField as! CRTextField
            if tf.text == ""{
                tf.changeLabel()
            }
            tf.changeLineHidden()
        }
        return true
    }
    func textFieldDidEndEditing(_ textField: UITextField) {
        if textField is CRTextField {
            let tf = textField as! CRTextField
            if tf.text == "" {
                tf.disChangeLabel()
            }
            tf.changeLineHidden()
        }
    }
}

github地址:EWTextField.

有问题欢迎探讨.