C# 微信永久素材

微信公众号自定义菜单media_id 类型需要永久素材图片，

1. 永久图片素材新增后，将带有url返回给开发者，开发者可以在腾讯系域名内使用。
2. 公众号的素材库保存数量有上限：图文消息素材、图片素材上限为100000，其他类型为1000。

这里只写新增图片素材接口：

http请求方式：POST，https https://api.weixin.qq.com/cgi-bin/material/add_material?access_token=ACCESS_TOKEN&type=TYPE （使用curl命令，用FORM表单方式新增一个其他类型的永久素材，curl命令的使用请自行查阅资料）

需要的参数：

返回的参数：

这个media_id就是公众号自定义菜单图片所需要的。

 上传新的素材：
 <asp:FileUpload ID="FileUpload1" runat="server" />
 <asp:Button ID="btn_save" runat="server" Text="保 存" CssClass="btn btn-blue shiny"  OnClick="btn_save_Click"/>
 <asp:Label ID="Label1" runat="server" ForeColor="Red"></asp:Label>

//上传素材
    protected void btn_save_Click(object sender, EventArgs e)
    {
        if (FileUpload1.PostedFile.FileName == "")
        {
            string nr = "请选择需要上传的图片！";
            this.Label1.Text = nr;
            this.btn_save.Enabled = true;
        }
        else
        {
            StringBuilder files = new StringBuilder();
            String path = Server.MapPath("~/CDR/");
            string extention = Path.GetExtension(this.FileUpload1.PostedFiles[0].FileName).ToLower();
            if (extention != ".jpg" && extention != ".png" && extention != ".png" && extention != ".gif")
            {
                this.Label1.Text = "允许上传的图片格式为jpg、jpeg、png和gif类型！";
                return;
            }
            if (this.FileUpload1.PostedFiles[0].ContentLength > 4194304)
            {
                this.Label1.Text = "上传的图片不允许超过4MB！";
                return;
            }
            string picname = DateTime.Now.ToString("yyyyMMddHHmmssfff") + extention;
            files.Append(picname);
            System.Drawing.Image image = System.Drawing.Image.FromStream(this.FileUpload1.PostedFiles[0].InputStream);
            bool flag = Utils.SaveImageForSpecifiedQuality(image, path + picname, 90);
            //将图片保存到文件内，
            if (flag == false)
            {
                this.Label1.Text = "保存失败";
                return;
            }
            string headimage = "绝对路径/CDR/" + files.ToString();
            string media = WxHttpRequest.UploadMultimedia("image", headimage);
            //将返回的json分成media_id 和url
            string media_id = GetJsonValue(media, "media_id");
            int i = SqlHelp.ExecuteSql("insert into wx_media(media_id,img,addTime) values('" + media_id + "','CDRImg/" + files.ToString() + "','" + DateTime.Now + "')");
            if (i > 0)
            {
                this.Label1.Text = "图片上传成功";
            }
            return;
        }
    }

 #region 微信永久素材上传
    /// <summary>
    /// 微信永久素材上传
    /// </summary>
    /// <param name="type">媒体文件类型，分别有图片（image）、语音（voice）、视频（video）和缩略图（thumb）</param>
    /// <param name="file">上传文件的绝对路径</param>
    /// <returns></returns>
    public static string UploadMultimedia(string type, string file)
    {
        string fileName = file;
        string url = string.Format("https://api.weixin.qq.com/cgi-bin/material/add_material?access_token=" + IsExistAccess_Token() + "&type=" + type);
        FileStream fs = new FileStream(file, FileMode.OpenOrCreate, FileAccess.Read);
        byte[] fileByte = new byte[fs.Length];
        fs.Read(fileByte, 0, fileByte.Length);
        fs.Close();
        //设置参数
        HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
        CookieContainer cookieContainer = new CookieContainer();
        request.CookieContainer = cookieContainer;
        request.AllowAutoRedirect = true;
        request.Method = "POST";
        string boundary = DateTime.Now.Ticks.ToString("X");//随机分割线
        request.ContentType = "multipart/form-data;charset=utf-8;boundary="+ boundary;
        byte[] itemBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--"+boundary+"\r\n");
        byte[] endBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");

        StringBuilder sbHeader =
                new StringBuilder(
                    string.Format(
                        "Content-Disposition:form-data;name=\"media\";filename=\"{0}\"\r\nContent-Type:application/octet-stream\r\n\r\n",
                        fileName));
        byte[] postHeaderBytes = Encoding.UTF8.GetBytes(sbHeader.ToString());

        Stream postStream = request.GetRequestStream();
        postStream.Write(itemBoundaryBytes,0,itemBoundaryBytes.Length);
        postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);
        postStream.Write(fileByte, 0, fileByte.Length);
        postStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);
        postStream.Close();

        HttpWebResponse response = request.GetResponse() as HttpWebResponse;
        Stream instream = response.GetResponseStream();
        StreamReader sr = new StreamReader(instream, Encoding.UTF8);
        string content = sr.ReadToEnd();

        return content;
    }
    #endregion