- (NSString *)replaceWithModelString:(NSString *)string{
    for (int i= 0 ; i < [string length]; i++)
    {
        NSString *s = [string substringWithRange:NSMakeRange(i, 1)]; // 字符串截取
        if ([s isEqualToString:@"<"])
        {
            NSRange range = NSMakeRange(i, 4);
            string = [string stringByReplacingCharactersInRange:range withString:@"\n"]; // 字符串替换
        }
    }
    return string;
}