Silverlight MVVM 异步数据未载入完就返回空数据

Silverlight MVVM 异步数据未载入完便返回空数据
Services\DataService.cs

C# code

        public List<User> GetAllUser()        {            List<User> userList = new List<User>();            LoadOperation lo = pcs.Load<Web.User>(pcs.GetUsersQuery());            pcs.Load<Web.User>(pcs.GetUsersQuery()).Completed += (s, a) =>            {                foreach (Web.User u in (s as LoadOperation<Web.User>).Entities)                {                    User user = new User();                    user.Name = u.user_name;                    user.Uid = u.user_id;                    user.Uiid = u.user_iid;                    userList.Add(user);                }            };            MessageBox.Show("2");            return userList;        }

ViewModels\UserMgrViewModel.cs

C# code

void LoadUserList()        {            DataService ds = new DataService();            this.UserList= new List<User>();            MessageBox.Show("1");            this.UserList= ds.GetAllUser();            MessageBox.Show("3");        }

弹出"1"后直接出"3",再出"2"...

请教大家用什么方法解决?

[解决办法]
异步本来就是这样的，跟同步编程是两回事。

程序的接口需要做出根本性的改变：

C# code

        public void GetAllUser(Action<List<User>> callback)        {            LoadOperation lo = pcs.Load<Web.User>(pcs.GetUsersQuery());            pcs.Load<Web.User>(pcs.GetUsersQuery()).Completed += (s, a) =>            {                List<User> userList = new List<User>();                foreach (Web.User u in (s as LoadOperation<Web.User>).Entities)                {                    User user = new User();                    user.Name = u.user_name;                    user.Uid = u.user_id;                    user.Uiid = u.user_iid;                    userList.Add(user);                }                callback(userList);            };        } 

 

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