iOS实现一个意见反馈类型的输入栏

@property (nonatomic, strong) UILabel *placholderLabel; //提示字符串 
@property (weak, nonatomic) IBOutlet UITextView *infoTF;
 
#define MAX_LIMIT_NUMS 120 //文本最大长度
 
- (void)controlView {
 self.infoTF.layer.borderWidth = 0.5;//边宽
 self.infoTF.layer.cornerRadius = 5.0;//设置圆角
 self.infoTF.layer.borderColor =[UIColor grayColor].CGColor;
 self.infoTF.delegate = self;
 
 CGFloat width = self.infoTF.frame.size.width;
 
 self.placholderLabel = [[UILabel alloc] initWithFrame:CGRectMake(5, 0, width-5, 30)];
 self.placholderLabel.numberOfLines = 0;
 self.placholderLabel.text = setInternational(@"live.weibosummay.string");
 self.placholderLabel.textColor = setRGBColor(176, 176, 176);
 self.placholderLabel.font = ZKP15Font;
 [self.placholderLabel setHidden:NO];
 [self.infoTF addSubview:_placholderLabel];
}
 
//限制文本输入长度
- (void)textViewDidChange:(UITextView*)textView{
 if([textView.text length] == 0){
  _placholderLabel.hidden = NO;
 }else{
  _placholderLabel.hidden = YES;//这里给空
 }
 
 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 > MAX_LIMIT_NUMS){
  //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:MAX_LIMIT_NUMS];
  
  [textView setText:s];
 }
}
//设置超出最大字数（120字）即不可输入 也是textview的代理方法
- (BOOL)textView:(UITextView*)textView shouldChangeTextInRange:(NSRange)range
 replacementText:(NSString*)text{
 
 UITextRange *selectedRange = [textView markedTextRange];
 //获取高亮部分
 UITextPosition *pos = [textView positionFromPosition:selectedRange.start offset:0];
 
 //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 < MAX_LIMIT_NUMS) {
   return YES;
  }else{
   return NO;
  }
 }
 
 NSString *comcatstr = [textView.text stringByReplacingCharactersInRange:range withString:text];
 
 NSInteger caninputlen = MAX_LIMIT_NUMS - 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) {
           
           NSInteger steplen = substring.length;
           if (idx >= rg.length) {
            *stop = YES; //取出所需要就break，提高效率
            return ;
           }
           
           trimString = [trimString stringByAppendingString:substring];
           
           idx = idx + steplen;//这里变化了，使用了字串占的长度来作为步长 
          }];
    
    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]];
  }
  return NO;
 }
}