/**
     * 内容中图片地址转成绝对地址
     * @param $content
     * @return mixed
     */
    private function imgUrl($content)
    {
        preg_match_all('/<img(.*)src="([^"]+)"[^>]+>/isU', $content, $matches);
        $vote_content = $content;
        $img = '';
        $imgDiv = '';
        if (!empty($matches)) {
            //注意，上面的正则表达式说明src的值是放在数组的第三个中
            $img = $matches[2];
            $imgDiv = $matches[0];
        } else {
            $img = '';
            $imgDiv = '';
        }
        if (!empty($img)) {
            $img_url = asset('');
            $patterns = array();
            $replacements = array();
            foreach ($img as $imgItem) {
                $final_imgUrl = $img_url . $imgItem;
                //获取文本中的所有图片
                $this->imgString[] = $final_imgUrl;
                $replacements[] = $final_imgUrl;
                $img_new = "/" . preg_replace("/\//i", "\/", $imgItem) . "/";
                $patterns[] = $img_new;
            }
            //让数组按照key来排序
            ksort($patterns);
            ksort($replacements);
            //替换内容
            $vote_content = preg_replace($patterns, $replacements, $content);
        }
        return $vote_content;

}