史上最好用的UITextview子类

gitDemo地址：https://github.com/laity1991/WKTextView

一.前言

• 之前做项目封装textView时存在一些bug一直未解决：文本信息在用户粘贴过长超出设定的最大字数时、带emoji时截取显示半个或乱码（因为emoji在iOS中使用的是UTF16也就是占位符是8+8两个字节的，占的长度为2,因此在计算字数时一个表情就占了2）

• 查了网上的一些封装demo，或是不太全或是存在一些小bug，在此我整理封装了一套WKTextView，方便大家使用和自己备用，主要解决问题：**
  1.添加了占位文本 ，类似于textField的placeholder 　
  2.中，英文字符输入时限制。
  3.带emoji时截取显示半个或乱码字符处理。
  4.处理了用户在粘贴过来文本超出字数限制存在bug的情况**
• ** 这里用到了我写的UIView的一个分类UIView+WKCategory (重写frame setter、getter方法)，注释比较详细，不做过多赘述**

二 .WKTextView源码

• *** WKTextView.h ***

  #import 
  @interface WKTextView : UITextView
  //文字
  @property(nonatomic,copy) NSString *myPlaceholder;
  //文字颜色
  @property(nonatomic,strong) UIColor *myPlaceholderColor;
  //最多输入字数
  @property (nonatomic, assign) NSInteger maxNum;
  ///右下角统计字数label
  @property (nonatomic, strong) UILabel *countLabel;
  @end
  

• *** WKTextView.m ***
  #import "WKTextView.h"
  #import "UIView+WKCategory.h"
  @interface WKTextView()
  @property (nonatomic,weak) UILabel *placeholderLabel;
  @end

  @implementation WKTextView
  
   - (instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if (self) {
    UILabel *placeholderLabel = [[UILabel alloc]init];
    [self addSubview:placeholderLabel];
    placeholderLabel.textColor = [UIColor lightGrayColor];
    self.placeholderLabel= placeholderLabel;
    UILabel *countLabel = [[UILabel alloc]init];
    [self addSubview:countLabel];
    countLabel.frame = CGRectMake(self.width - 60, self.height - 40, 60, 40);
    countLabel.textAlignment = NSTextAlignmentCenter;
    countLabel.textColor = [UIColor lightGrayColor];
    countLabel.text = @"0/100";
    self.countLabel = countLabel;
    ///设置边框
    self.layer.masksToBounds = YES;
    self.layer.cornerRadius = 4;
    self.layer.borderColor = [UIColor grayColor].CGColor;
    self.layer.borderWidth = 1;
    
    self.delegate = self;
    return self;
  }
  - (void)layoutSubviews{
      [super layoutSubviews];
      self.placeholderLabel.x = 8;
      self.placeholderLabel.y = 8;
      self.placeholderLabel.width = self.width - 
      2*self.placeholderLabel.x;
      ///根据占位文字myPlaceholder 算出占位Label的高度(宽度已定 高速自适应)
      CGSize maxSize = CGSizeMake(self.placeholderLabel.width, MAXFLOAT);
      self.placeholderLabel.height = [self.myPlaceholder boundingRectWithSize:maxSize 
      options:NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:self.placeholderLabel.font} context:nil].size.height;
  }
  
  ///箭头textView的输入文字变化 以此控制占位label的显示和隐藏
  - (void)textDidChange{
     //hasText是UITextView的属性 如果textView输入了文字就是
     YES 没有文字就是NO
      self.placeholderLabel.hidden = self.hasText;
  
  }
  
  #pragma mark - UITextViewDelegate
  
  - (BOOL)textView:(UITextView *)textView 
     shouldChangeTextInRange:(NSRange)range 
     replacementText:(NSString *)text{
     if ([text isEqualToString:@"\n"]) {
    [self resignFirstResponder];
    return NO;
   }
  UITextRange *selectedRange = [textView markedTextRange];
  //获取高亮部分
   UITextPosition *pos = [textView 
   positionFromPosition:selectedRange.start offset:0];
   //获取高亮部分内容
   //NSString * selectedtext = [textView 
   textInRange:selectedRange];
  
  //如果有高亮且当前字数开始位置小于最大限制时允许输入
    if (selectedRange && pos) {
    NSInteger startOffset = [textView offsetFromPosition:textView.beginningOfDocument toPosition:selectedRange.start];
    NSInteger endOffset = [textView offsetFromPosition:textView.beginningOfDocument toPosition:selectedRange.end];
    NSRange offsetRange = NSMakeRange(startOffset, endOffset - startOffset);
    
    if (offsetRange.location < self.maxNum) {
        return YES;
    }
    else
    {
        return NO;
    }
   }
     NSString *comcatstr = [textView.text stringByReplacingCharactersInRange:range withString:text];
  
     NSInteger caninputlen = self.maxNum - comcatstr.length;
  
     if (caninputlen >= 0)
     {
    return YES;
      }
      else
      {
    NSInteger len = text.length + caninputlen;
    //防止当text.length + caninputlen < 0时，使得rg.length为一个非法最大正数出错
    NSRange rg = {0,MAX(len,0)};
    
    if (rg.length > 0)
    {
        NSString *s = @"";
        //判断是否只普通的字符或asc码(对于中文和表情返回NO)
        BOOL asc = [text canBeConvertedToEncoding:NSASCIIStringEncoding];
        if (asc) {
            s = [text substringWithRange:rg];//因为是ascii码直接取就可以了不会错
                 }
        else
        {
            __block NSInteger idx = 0;
            __block NSString  *trimString = @"";//截取出的字串
            //使用字符串遍历，这个方法能准确知道每个emoji是占一个unicode还是两个
            [text enumerateSubstringsInRange:NSMakeRange(0, [text length])
                                     options:NSStringEnumerationByComposedCharacterSequences
                                  usingBlock: ^(NSString* substring, NSRange substringRange, NSRange enclosingRange, BOOL* stop) {
                                      
                                      if (idx >= rg.length) {
                                          *stop = YES; //取出所需要就break，提高效率
                                          return ;
                                      }
                                      
                                      trimString = [trimString stringByAppendingString:substring];
                                      
                                      idx++;
                                  }];
            
            s = trimString;
        }
        //rang是指从当前光标处进行替换处理(注意如果执行此句后面返回的是YES会触发didchange事件)
        [textView setText:[textView.text stringByReplacingCharactersInRange:range withString:s]];
        //既然是超出部分截取了，哪一定是最大限制了。
        self.countLabel.text = [NSString stringWithFormat:@"%ld/%ld",(long)self.maxNum,(long)self.maxNum];
        
    }
    return NO;
     }
    }
  
    - (void)textViewDidChange:(UITextView *)textView{
      self.placeholderLabel.hidden = self.hasText;
       UITextRange *selectedRange = [textView markedTextRange];
      //获取高亮部分
      UITextPosition *pos = [textView positionFromPosition:selectedRange.start offset:0];
  
     //如果在变化中是高亮部分在变，就不要计算字符了
     if (selectedRange && pos) {
    return;
     }
  
     NSString  *nsTextContent = textView.text;
     NSInteger existTextNum = nsTextContent.length;
  
     if (existTextNum > self.maxNum)
     {
    //截取到最大位置的字符(由于超出截部分在should时被处理了所在这里这了提高效率不再判断)
    NSString *s = [nsTextContent substringToIndex:self.maxNum];
    
    [textView setText:s];
    }
    if (existTextNum > 100) {
     existTextNum = 100;
      }
     //不让显示负数
   self.countLabel.text = [NSString 
   stringWithFormat:@"%ld/%ld",MAX(0, existTextNum),
   (long)self.maxNum
                        ];
  
   }
   #pragma mark - setter
  
  - (void)setMaxNum:(NSInteger)maxNum{
     _maxNum = maxNum;
      self.countLabel.text = [NSString stringWithFormat:@"0/%ld",
     (long)_maxNum];
    }
  
  - (void)setMyPlaceholder:(NSString *)myPlaceholder{
        _myPlaceholder = myPlaceholder;
        self.placeholderLabel.text = _myPlaceholder;
        ///重新计算占位label frame
        [self setNeedsLayout];
      }
  
  - (void)setMyPlaceholderColor:(UIColor *)myPlaceholderColor{
            _myPlaceholderColor = myPlaceholderColor;
            self.countLabel.textColor = myPlaceholderColor;
            self.placeholderLabel.textColor = _myPlaceholderColor;
        }
  
    ///从写TextView setFont方法 使占位labe、TextView、文字统计
      Label Font一致
  - (void)setFont:(UIFont *)font{
            [super setFont:font];
            self.placeholderLabel.font = font;
            self.countLabel.font = font;
            ///重新计算占位label frame
            [self setNeedsLayout];
       }
      @end
  

• *** Demo ***

     - (void)prepareForUI{
              ///添加到父控件
              WKTextView *textView = [[WKTextView alloc]initWithFrame:CGRectMake(50, 50, self.view.width - 100, 200)];
              ///设置文本输入框的占位字符
              textView.myPlaceholder = @"我是占位字符串...";
              textView.font = [UIFont systemFontOfSize:14];
              textView.maxNum = 100;
              [self.view addSubview:textView];
          }
  

• 相关属性都暴露了出来，可以自行设置，效果如下：

WKTextView.gif