键盘字数限制

#pragma mark - UITextView Delegate

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{

    UITextRange *selectedRange = [textField markedTextRange];
    //获取高亮部分
    UITextPosition *pos = [textField 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 = [textField offsetFromPosition:textField.beginningOfDocument toPosition:selectedRange.start];
        NSInteger endOffset = [textField offsetFromPosition:textField.beginningOfDocument toPosition:selectedRange.end];
        NSRange offsetRange = NSMakeRange(startOffset, endOffset - startOffset);

        if (offsetRange.location < MAX_STARWORDS_LENGTH) {
            return YES;
        }
        else
        {
            return NO;
        }
    }

    NSString *comcatstr = [textField.text stringByReplacingCharactersInRange:range withString:string];

    NSInteger caninputlen = MAX_STARWORDS_LENGTH - comcatstr.length;

    if (caninputlen >= 0)
    {
        return YES;
    }
    else
    {
        NSInteger len = string.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 = [string canBeConvertedToEncoding:NSASCIIStringEncoding];
            if (asc) {
                s = [string 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
                [string enumerateSubstringsInRange:NSMakeRange(0, [string 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)
            [textField setText:[textField.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.lbNums.text = [NSString stringWithFormat:@"%d/%ld",0,(long)MAX_STARWORDS_LENGTH];
        }
        return NO;
    }
}
// 计算转换后字符的个数

- (NSUInteger) lenghtWithString:(NSString *)string
{
    NSUInteger len = string.length;
    // 汉字字符集
    NSString * pattern  = @"[\u4e00-\u9fa5]";
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern options:NSRegularExpressionCaseInsensitive error:nil];
    // 计算中文字符的个数
    NSInteger numMatch = [regex numberOfMatchesInString:string options:NSMatchingReportProgress range:NSMakeRange(0, len)];

    return len + numMatch;
}

#pragma mark - Notification Method
-(void)textFieldDidChange:(UITextField *)textField
{
    UITextRange *selectedRange = [textField markedTextRange];
    //获取高亮部分
    UITextPosition *pos = [textField 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 = textField.text;
    NSInteger existTextNum = nsTextContent.length;

    if (existTextNum > MAX_STARWORDS_LENGTH)
    {
        //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_STARWORDS_LENGTH];

        [textField setText:s];
    }

    //不让显示负数 口口日
    self.limitLabel.text = [NSString stringWithFormat:@"%lu",MAX(0,MAX_STARWORDS_LENGTH - textField.text.length)];
}