/// <summary>
/// 用户离线【移除缓存】
/// </summary>
/// <returns></returns>
public async Task <bool> UserOffline()
{
var cid = Context.ConnectionId;
cache.RemoveByValue(cid);
await Clients.Client(cid).SendAsync("ReceiveAlarmVoice", -3, new { title = "系统消息", content = "离线成功" });
return(true);
}