微信查询所有关注该公众号的用户

using (HttpClient client = new HttpClient())
{
    var appId = "";
    var appSecret = "";
    //起始位置，为空则从头开始查询
    var next_openid = "";
    //注册一次即可
    AccessTokenContainer.Register(appId, appSecret);
    var token = AccessTokenContainer.GetAccessToken(appId);
    string url = string.Format("https://api.weixin.qq.com/cgi-bin/user/get?access_token={0}", token);
    if (!string.IsNullOrEmpty(next_openid))
    {
        url += "&next_openid=" + next_openid;
    }
    var response = await client.GetAsync(url);
    var resultStr = await response.Content.ReadAsStringAsync();
    GetAllUsersOutput result = JsonConvert.DeserializeObject<GetAllUsersOutput>(resultStr);
}

public class GetAllUsersOutput
{
    public int total { get; set; }
    public int count { get; set; }
    public GetAllUsersData data { get; set; }
    public string next_openid { get; set; }
}

public class GetAllUsersData
{
    public List<string> openid { get; set; }
}

示例代码

示例代码