最近这段时间在搞一个Swift的项目，算是帮朋友做的吧，虽然有点累但是自己也是从中学到了很多东西，其中自己也封装了一些常用的控件，最近忙完公司的项目以后就整理一下自己的心得。。希望大家一起学习！

最近项目需要，很多的地方都用到了UITextView来实现一些需求，需要设置占位词和最大的长度，这里我是简单的封装了一下，希望大家多多指正，话不多说，上代码：

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {

        if text == "\n"{ // 输入换行符时收起键盘
            textView.resignFirstResponder() // 收起键盘
            return false
        }

        if text != "" {
             self.placeHolderLabel.isHidden = true // 隐藏
        }

        let textStr = NSString.init(format: "%@", text)

        if textStr.isEqual(to: "") && range.length == 1 && range.location == 0 {
            self.placeHolderLabel.isHidden = false // 隐藏
        }

        /// 字数统计
        let lengthOfString :NSInteger = textStr.length

        let fieldTextString : String = textV.text

        let proposedNewLength : Int =  fieldTextString.count - range.length + lengthOfString;

        maxLengthNum.text = NSString.init(format: "%ld/%ld", proposedNewLength, maxNumber) as String

        if proposedNewLength >= maxNumber + 1 {
            Logger.d("已到字数限制")
            let textVStr = textV.text as NSString
            let str = textVStr.substring(to: maxNumber)
            textV.text = str
            maxLengthNum.text = NSString.init(format: "%ld/%ld", maxNumber, maxNumber) as String
            return false
        }
        return true
    } 

在 UITextView的代理方法中监听内容的变化，来判断占位词的显示和隐藏，设置当前的字数以及最大长度，这里对字数的统计比较重要，我是根据当前输入的内容的位置来进行计算。

全部代码：

import UIKit

class LZHTextView: UIView, UITextViewDelegate {

    /** 占位词 **/
    let placeHolderLabel = UILabel()

    /** 字数限制 **/
    let maxLengthNum = UILabel()

    /** 最大字数 **/
    var maxNumber: NSInteger = 0

    /** 文本View */
    let textV = UITextView()

    override init(frame: CGRect) {
        super.init(frame: frame)

        textV.backgroundColor = .white
        textV.returnKeyType = .done
        textV.font = APP_FONT_14_NORMAL()
        textV.textColor = .black
        textV.delegate = self
        self.addSubview(textV)
        textV.snp.makeConstraints { (make) in
            make.top.left.right.equalToSuperview()
            make.bottom.equalToSuperview().offset(-20)
        }

        placeHolderLabel.textColor = RGBColor(135, g: 135, b: 135)
        placeHolderLabel.font = APP_FONT_12_SAMALL()
        placeHolderLabel.isHidden = false
        textV.addSubview(placeHolderLabel)
        placeHolderLabel.snp.makeConstraints { (make) in
            make.left.equalToSuperview().offset(5)
            make.right.right.equalToSuperview()
            make.top.equalToSuperview()
            make.height.equalTo(25)
        }

        /// 字数限制
        maxLengthNum.textColor = APP_Main_GrayText_COLOR
        maxLengthNum.font = APP_FONT_12_SAMALL()
        maxLengthNum.textAlignment = .center
        self.addSubview(maxLengthNum)
        maxLengthNum.snp.makeConstraints { (make) in
            make.bottom.equalToSuperview()
            make.right.equalToSuperview().offset(-10)
            make.width.equalTo(50)
            make.height.equalTo(20)
        }
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    /**
     * 设置占位词
     */
    func setPlaceHolder(holderStr: String) -> Void {
        placeHolderLabel.text = holderStr
    }

    /**
     * 设置字数限制
     */
    func setContentMaxLength(length: NSInteger) -> Void {

        if length == 0 {
            maxLengthNum.isHidden = true
        } else {
            maxLengthNum.isHidden = false
            maxLengthNum.text = NSString.init(format: "0/%ld", length) as String
        }

        maxNumber = length
    }

    func textViewShouldBeginEditing(_ textView: UITextView) -> Bool {
        self.placeHolderLabel.isHidden = true // 隐藏
        return true
    }

    func textViewDidEndEditing(_ textView: UITextView) {
        if textView.text.isEmpty {
           self.placeHolderLabel.isHidden = false // 显示
        }
    }

    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {

        if text == "\n"{ // 输入换行符时收起键盘
            textView.resignFirstResponder() // 收起键盘
            return false
        }

        if text != "" {
             self.placeHolderLabel.isHidden = true // 隐藏
        }

        let textStr = NSString.init(format: "%@", text)

        if textStr.isEqual(to: "") && range.length == 1 && range.location == 0 {
            self.placeHolderLabel.isHidden = false // 隐藏
        }

        /// 字数统计
        let lengthOfString :NSInteger = textStr.length

        let fieldTextString : String = textV.text

        let proposedNewLength : Int =  fieldTextString.count - range.length + lengthOfString;

        maxLengthNum.text = NSString.init(format: "%ld/%ld", proposedNewLength, maxNumber) as String

        if proposedNewLength >= maxNumber + 1 {
            Logger.d("已到字数限制")
            let textVStr = textV.text as NSString
            let str = textVStr.substring(to: maxNumber)
            textV.text = str
            maxLengthNum.text = NSString.init(format: "%ld/%ld", maxNumber, maxNumber) as String
            return false
        }
        return true
    }
} 

里面修改一些字体大小的设置以及颜色，引入SnapKit框架就可以直接用，有不足的地方还望大佬们指正。