二、获取微信用户openId

/// <summary>
/// 登录首页
/// </summary>
/// <returns></returns>
public ActionResult Index()
{
    if (Session["isTrue"] == null)
    {
        string weixinAppid = System.Configuration.ConfigurationManager.AppSettings["weixinAppid"];
        string weixinBackUrl = System.Configuration.ConfigurationManager.AppSettings["weixinBackUrl"];
        var url = string.Format("//open.weixin.qq.com/connect/oauth2/authorize?appid={0}&redirect_uri={1}&response_type=code&scope=snsapi_base&state=STATE#wechat_redirect", weixinAppid, weixinBackUrl);
        return Redirect(url); //会跳转到weixinBackUrl填写的地址(NewHome)上并将code值发过去
    }
    return View();
}

public class NewHomeController : BaseController
{
    public ActionResult Index(string code)
    {
        string openId = GetOpenId(code);
    }
    
    /// <summary>
    /// 获取openId
    /// </summary>
    /// <param name="code"></param>
    /// <returns></returns>
    public static string GetOpenId(string code)
    {
        string url = string.Format("https://api.weixin.qq.com/sns/oauth2/access_token?appid={0}&secret={1}&code={2}&grant_type=authorization_code", weixinAppid, weixinSecret, code); //weixinAppid和weixinSecret为公众号的appID和appsecret

        var client = new System.Net.WebClient();
        client.Encoding = System.Text.Encoding.UTF8;
        string data = client.DownloadString(url);
        JavaScriptSerializer Jss = new JavaScriptSerializer();
        UserInfo userInfo = Jss.Deserialize<UserInfo>(data);
        return userInfo.OpenId;
    }
}

public class UserInfo
{
    /// <summary>
    /// 用户是否订阅该公众号标识，值为0时，代表此用户没有关注该公众号，拉取不到其余信息
    /// </summary>
    public int SubScribe { get; set; }
    /// <summary>
    /// 用户的标识，对当前公众号唯一
    /// </summary>
    public string OpenId { get; set; }
    /// <summary>
    /// 用户的昵称
    /// </summary>
    public string NickName { get; set; }
    /// <summary>
    /// 用户的性别，值为1时是男性，值为2时是女性，值为0时是未知
    /// </summary>
    public int Sex { get; set; }
    /// <summary>
    /// 语言
    /// </summary>
    public string Language { get; set; }
    /// <summary>
    /// 用户所在城市
    /// </summary>
    public string City { get; set; }
    /// <summary>
    /// 用户所在省份
    /// </summary>
    public string Province { get; set; }
    /// <summary>
    /// 用户所在国家
    /// </summary>
    public string Country { get; set; }
    /// <summary>
    /// 用户头像，最后一个数值代表正方形头像大小（有0、46、64、96、132数值可选，0代表640*640正方形头像），用户没有头像时该项为空。若用户更换头像，原有头像URL将失效
    /// </summary>
    public string Headimgurl { get; set; }
    /// <summary>
    /// 用户关注时间，为时间戳。如果用户曾多次关注，则取最后关注时间
    /// </summary>
    public int Subscribe_time { get; set; }
    /// <summary>
    /// 只有在用户将公众号绑定到微信开放平台帐号后，才会出现该字段
    /// </summary>
    public string Unionid { get; set; }
    /// <summary>
    /// 公众号运营者对粉丝的备注，公众号运营者可在微信公众平台用户管理界面对粉丝添加备注
    /// </summary>
    public string Remark { get; set; }
    /// <summary>
    /// 用户所在的分组ID
    /// </summary>
    public int Groupid { get; set; }
}