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; }}