Silverlight中的嵌套异步函数

我认为通过添加几个辅助函数可以使您的工作更轻松。第一个是异步函数，用于检查用户是否唯一。如果出现错误，您可能需要添加一些代码来设置tcs.SetException。

private Task<bool> IsUserUniqueAsync(UserViewModel user, DatabaseServiceLocal dataService)
{
    var tcs = new TaskCompletionSource<bool>();
    dataService.CheckIsUserNameUnique += (s, e) =>
                        {
                            tcs.SetResult(e.IsUnique);
                        };
    dataService.IsUserNameUnique(user.UserName, user.UserID, Database.CurrentClient.ClientID);
    return tcs.Task;
}

第二个异步更新所有用户

public Task<bool> UpdateUsersAsync(ObservableCollection<User> updatedUsers, DatabaseServiceLocal dataService)
{
    var tcs = new TaskCompletionSource<bool>();
    BusyIndicator = true;
    BusyMessage = "Saving...";
    dataService.UpdateStaffAndUsersCompleted += (s, e) =>
                {
                    BusyIndicator = false;
                    tcs.SetResult(e.Success);                 
                 };
    dataService.UpdateUsers(Database.CurrentProject.ProjectID, Database.CurrentClient.ClientID, updatedUsers, _DeletedProjectUsers);
    return tcs.Task;
}

那么你的SaveUsers方法就变得简单了一点。

private async void SaveUsers(bool CloseForm)
{
    ObservableCollection<User> _UpdatedUsers = new ObservableCollection<User>(); 
    DatabaseServiceLocal _dataService = new DatabaseServiceLocal(Database);
    Dictionary<Task<bool>, User> tasks = new Dictionary<Task<bool>, User>();
    // start all tasks in parallel
    foreach (UserViewModel _User in _AllUsers)
    {
        if (_User.Dirty && !_User.IsBlank)
        { 
            tasks.Add(IsUserUniqueAsync(_User, _dataService), _User);       
        }
    }           
    // process each task as it completes
    while(tasks.Count() > 0 )
    {
        var task = await Task.WhenAny(tasks.Keys.ToArray());
        if(task.Result)
        {
            _UpdatedUsers.Add(_User.SaveAsUser()); 
        }
        else
        {
           MessageBox.Show(string.Format("Username {0} is not allowed as it already exists in the system. Please choose a different username.", ""), null);
           return;
        }
        tasks.Remove(task);
    }
    if( await UpdateUsersAsync(_UpdatedUsers, _dataService))
    {
        if (CloseForm)
            ReturnToHomePage();
        else
        {
            LoadUsers();
            OnUsersSaved();
        }
    }
}

您的代码大致是这样的:

ObservableCollection<User> _UpdatedUsers = new ObservableCollection<User>();
int _verifiedUsersCount = 0;
DatabaseServiceLocal _dataService = new DatabaseServiceLocal(Database);
//Verify unique users
private void SaveUsers(bool CloseForm)
{
    _dataService.CheckIsUserNameUnique += CheckIsUserNameUnique;
    foreach (UserViewModel _User in _AllUsers)
    {
        //bool success = _dataService.IsUserNameUnique(_User.UserName, _User.UserID, Database.CurrentClient.ClientID);
        if (_User.Dirty && !_User.IsBlank)
        {
            _dataService.IsUserNameUnique(_User.UserName, _User.UserID, Database.CurrentClient.ClientID);
        }
    }
}
//Store verified users to save
private void CheckIsUserNameUnique(object s, CheckIsUserNameUniqueEventArgs e)
{
    if (e.IsUnique)
        _UpdatedUsers.Add(_User.SaveAsUser());
    else
    {
        csaMessageBox.Show(string.Format("Username {0} is not allowed as it already exists in the system. Please choose a different username.", ""), null);
    }
    verifiedUsersCount++;
    //Call after all the users have been verified for uniqueness
    if (_AllUsers.Count() == verifiedUsersCount)
    {
        OnUniqueUserVerifyComplete();
    }
}
//Save verified users
private void OnUniqueUserVerifyComplete()
{
    //No unique users 
    if (_UpdatedUsers.Count < 1) { return; }
    _dataService.UpdateStaffAndUsersCompleted += (s, e) =>
    {
        BusyIndicator = false;
        if (e.Success)
        {
        }
        if (CloseForm)
            ReturnToHomePage();
        else
        {
            LoadUsers();
            OnUsersSaved();
        }
    };
    BusyIndicator = true;
    BusyMessage = "Saving...";
    _dataService.UpdateUsers(Database.CurrentProject.ProjectID, Database.CurrentClient.ClientID, _UpdatedUsers, _DeletedProjectUsers);
}