实现效果：1.@好友 文本颜色，字体改变
2.@好友整体删除

代码详解：
1.找到所有"@xxx "格式的文本，@好友后加空格形成一种格式

#define kATFormat  @"@%@ "
#define kATRegular @"@[\\u4e00-\\u9fa5\\w\\-\\_]+ "
- (NSArray<NSTextCheckingResult *> *)findAllAt
{
    // 找到文本中所有的@
    NSString *string = self.sayTextView.text;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:kATRegular options:NSRegularExpressionCaseInsensitive error:nil];
    NSArray *matches = [regex matchesInString:string options:NSMatchingReportProgress range:NSMakeRange(0, [string length])];
    return matches;
}

2.textview文本改变除@好友 之外别的字体设置

- (void)textViewDidChange:(UITextView *)textView{
    
    UITextRange *selectedRange = textView.markedTextRange;
    NSString *newText = [textView textInRange:selectedRange];
    
    if (newText.length < 1)
    {
        // 高亮输入框中的@
        UITextView *textView = self.sayTextView;
        NSRange range = textView.selectedRange;
        
        NSMutableAttributedString *string = [[NSMutableAttributedString alloc] initWithString:textView.text];
        [string addAttribute:NSForegroundColorAttributeName value:[UIColor blackColor] range:NSMakeRange(0, string.string.length)];
        [string addAttribute:NSFontAttributeName value:KFont(14) range:NSMakeRange(0, string.string.length)];
        
        NSArray *matches = [self findAllAt];
        
        for (NSTextCheckingResult *match in matches)
        {
            [string addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:NSMakeRange(match.range.location, match.range.length - 1)];
            [string addAttribute:NSFontAttributeName value:KFont(14) range:NSMakeRange(match.range.location, match.range.length - 1)];
        }
        
        textView.attributedText = string;
        textView.selectedRange = range;
    }
}

3.光标不能落在@词中间

- (void)textViewDidChangeSelection:(UITextView *)textView{
    
    // 光标不能点落在@词中间
    NSRange range = textView.selectedRange;
    if (range.length > 0)
    {
        // 选择文本时可以
        return;
    }
    NSArray *matches = [self findAllAt];
    for (NSTextCheckingResult *match in matches)
    {
        NSRange newRange = NSMakeRange(match.range.location + 1, match.range.length - 1);
        
        if (NSLocationInRange(range.location, newRange))
        {
            textView.selectedRange = NSMakeRange(match.range.location + match.range.length, 0);
            break;
        }
    }
}

4.整体删除@好友

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range
 replacementText:(NSString *)text {
    
    if ([text isEqualToString:@""])
    {
        NSRange selectRange = textView.selectedRange;
        if (selectRange.length > 0)
        {
            //用户长按选择文本时不处理
            return YES;
        }
        // 判断删除的是一个@中间的字符就整体删除
        NSMutableString *string = [NSMutableString stringWithString:textView.text];
        NSArray *matches = [self findAllAt];
        BOOL inAt = NO;
        NSInteger index = range.location;
        for (NSTextCheckingResult *match in matches)
        {
            NSRange newRange = NSMakeRange(match.range.location + 1, match.range.length - 1);
            if (NSLocationInRange(range.location, newRange))
            {
                NSString *matchStr = [string substringWithRange:NSMakeRange(match.range.location, match.range.length - 1)];
                [_atDic removeObjectForKey:matchStr];
                inAt = YES;
                index = match.range.location;
                [string replaceCharactersInRange:match.range withString:@""];
                break;
            }
        }
        if (inAt)
        {
            textView.text = string;
            NSMutableAttributedString *attributeString = [[NSMutableAttributedString alloc] initWithString:string];
            [attributeString addAttribute:NSForegroundColorAttributeName value:[UIColor blackColor] range:NSMakeRange(0, attributeString.string.length)];
            [attributeString addAttribute:NSFontAttributeName value:KFont(14) range:NSMakeRange(0, attributeString.string.length)];
            NSArray *matches = [self findAllAt];
            
            for (NSTextCheckingResult *match in matches)
            {
                [attributeString addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:NSMakeRange(match.range.location, match.range.length - 1)];
                [attributeString addAttribute:NSFontAttributeName value:KFont(14) range:NSMakeRange(match.range.location, match.range.length - 1)];
            }
            textView.attributedText = attributeString;
            textView.selectedRange = NSMakeRange(index, 0);
            return NO;
        }
    }
    //判断是回车键就发送出去
    if ([text isEqualToString:@"\n"])
    {
        [textView resignFirstResponder];
        return NO;
    }
    return YES;
}

5.获取@好友的好友Id

 NSArray *matches = [self findAllAt];
 NSMutableArray *strArr = [NSMutableArray arrayWithCapacity:0];
 for (NSTextCheckingResult *match in matches)
 {
           
         NSString *matchStr = [self.sayTextView.text substringWithRange:NSMakeRange(match.range.location, match.range.length - 1)];
         [strArr addObject:[_atDic objectForKey:matchStr]];
 }    

6.添加@好友的好友Id

NSString *insertString = [NSString stringWithFormat:kATFormat,atUserName];
NSString *keyString = [NSString stringWithFormat:@"@%@",atUserName];
[_atDic setValue:atUserId forKey:keyString];