C#微信公众平台开发之高级群发接口

涉及access_token的获取请参考《C#微信公众平台开发之access_token的获取存储与更新》

一、为了实现高级群发功能，需要解决的问题

1、通过微信接口上传图文消息素材时，Json中的图片不是url而是media_id，如何通过微信接口上传图片并获取图片的media_id？

2、图片存储在什么地方，如何获取？

二、实现步骤，以根据OpenID列表群发图文消息为例

1、准备数据

    我把数据存储在数据库中，ImgUrl字段是图片在服务器上的相对路径(这里的服务器是自己的服务器，不是微信的哦)。

从数据库中获取数据放到DataTable中：

DataTable dt = ImgItemDal.GetImgItemTable(loginUser.OrgID, data);

2、通过微信接口上传图片，返回图片的media_id

 取ImgUrl字段数据，通过MapPath方法获取图片在服务器上的物理地址，用FileStream类读取图片，并上传给微信

HTTP上传文件代码(HttpRequestUtil类)：

/// <summary>
/// Http上传文件
/// </summary>
public static string HttpUploadFile(string url, string path)
{
 // 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"); // 随机分隔线
 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");

 int pos = path.LastIndexOf("\\");
 string fileName = path.Substring(pos + 1);

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

 FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);
 byte[] bArr = new byte[fs.Length];
 fs.Read(bArr, 0, bArr.Length);
 fs.Close();

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

 //发送请求并获取相应回应数据
 HttpWebResponse response = request.GetResponse() as HttpWebResponse;
 //直到request.GetResponse()程序才开始向目标网页发送Post请求
 Stream instream = response.GetResponseStream();
 StreamReader sr = new StreamReader(instream, Encoding.UTF8);
 //返回结果网页（html）代码
 string content = sr.ReadToEnd();
 return content;
}

请求微信接口，上传图片，返回media_id(WXApi类)：

/// <summary>
/// 上传媒体返回媒体ID
/// </summary>
public static string UploadMedia(string access_token, string type, string path)
{
 // 设置参数
 string url = string.Format("http://file.api.weixin.qq.com/cgi-bin/media/upload?access_token={0}&type={1}", access_token, type);
 return HttpRequestUtil.HttpUploadFile(url, path);
}

string msg = WXApi.UploadMedia(access_token, "image", path); // 上图片返回媒体ID
string media_id = Tools.GetJsonValue(msg, "media_id");

传入的path(aspx.cs文件中的代码)：

string path = MapPath(data);

一个图文消息由若干条图文组成，每条图文有标题、内容、链接、图片等

遍历每条图文数据，分别请求微信接口，上传图片，获取media_id

3、上传图文消息素材

拼接图文消息素材Json字符串(ImgItemDal类(操作图文消息表的类))：

/// <summary>
/// 拼接图文消息素材Json字符串
/// </summary>
public static string GetArticlesJsonStr(PageBase page, string access_token, DataTable dt)
{
 StringBuilder sbArticlesJson = new StringBuilder();

 sbArticlesJson.Append("{\"articles\":[");
 int i = 0;
 foreach (DataRow dr in dt.Rows)
 {
 string path = page.MapPath(dr["ImgUrl"].ToString());
 if (!File.Exists(path))
 {
  return "{\"code\":0,\"msg\":\"要发送的图片不存在\"}";
 }
 string msg = WXApi.UploadMedia(access_token, "image", path); // 上图片返回媒体ID
 string media_id = Tools.GetJsonValue(msg, "media_id");
 sbArticlesJson.Append("{");
 sbArticlesJson.Append("\"thumb_media_id\":\"" + media_id + "\",");
 sbArticlesJson.Append("\"author\":\"" + dr["Author"].ToString() + "\",");
 sbArticlesJson.Append("\"title\":\"" + dr["Title"].ToString() + "\",");
 sbArticlesJson.Append("\"content_source_url\":\"" + dr["TextUrl"].ToString() + "\",");
 sbArticlesJson.Append("\"content\":\"" + dr["Content"].ToString() + "\",");
 sbArticlesJson.Append("\"digest\":\"" + dr["Content"].ToString() + "\",");
 if (i == dt.Rows.Count - 1)
 {
  sbArticlesJson.Append("\"show_cover_pic\":\"1\"}");
 }
 else
 {
  sbArticlesJson.Append("\"show_cover_pic\":\"1\"},");
 }
 i++;
 }
 sbArticlesJson.Append("]}");

 return sbArticlesJson.ToString();
}

上传图文消息素材，获取图文消息的media_id：

/// <summary>
/// 请求Url，发送数据
/// </summary>
public static string PostUrl(string url, string postData)
{
 byte[] data = Encoding.UTF8.GetBytes(postData);

 // 设置参数
 HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
 CookieContainer cookieContainer = new CookieContainer();
 request.CookieContainer = cookieContainer;
 request.AllowAutoRedirect = true;
 request.Method = "POST";
 request.ContentType = "application/x-www-form-urlencoded";
 request.ContentLength = data.Length;
 Stream outstream = request.GetRequestStream();
 outstream.Write(data, 0, data.Length);
 outstream.Close();

 //发送请求并获取相应回应数据
 HttpWebResponse response = request.GetResponse() as HttpWebResponse;
 //直到request.GetResponse()程序才开始向目标网页发送Post请求
 Stream instream = response.GetResponseStream();
 StreamReader sr = new StreamReader(instream, Encoding.UTF8);
 //返回结果网页（html）代码
 string content = sr.ReadToEnd();
 return content;
}

/// <summary>
/// 上传图文消息素材返回media_id
/// </summary>
public static string UploadNews(string access_token, string postData)
{
 return HttpRequestUtil.PostUrl(string.Format("https://api.weixin.qq.com/cgi-bin/media/uploadnews?access_token={0}", access_token), postData);
}

string articlesJson = ImgItemDal.GetArticlesJsonStr(this, access_token, dt);
string newsMsg = WXApi.UploadNews(access_token, articlesJson);
string newsid = Tools.GetJsonValue(newsMsg, "media_id");

4、群发图文消息

获取全部关注者OpenID集合(WXApi类)：

/// <summary>
/// 获取关注者OpenID集合
/// </summary>
public static List<string> GetOpenIDs(string access_token)
{
 List<string> result = new List<string>();

 List<string> openidList = GetOpenIDs(access_token, null);
 result.AddRange(openidList);

 while (openidList.Count > 0)
 {
 openidList = GetOpenIDs(access_token, openidList[openidList.Co