/// <summary>
/// 群发图文消息给所有用户
/// </summary>
/// <param name="appId"></param>
/// <param name="nextOpenId"></param>
/// <returns></returns>
public async Task <SendResult> SendNewsToAllUsersAsync(string appId, string mediaId)
{
return(await GroupMessageApi.SendGroupMessageByGroupIdAsync(appId, null, mediaId,
GroupMessageType.mpnews, true, true));
}