WCF错误——无法找到引用合同“UserService.UserService”的默认端点元素

Any ideas how to fix this?

有办法解决这个问题吗?

UserService.UserServiceClient userServiceClient = new UserServiceClient();
            userServiceClient.GetUsersCompleted += new EventHandler<GetUsersCompletedEventArgs>(userServiceClient_GetUsersCompleted);
            userServiceClient.GetUsersAsync(searchString);
User