ContinueWith after PostAsJsonAsyc - vb.net

Question

I've got a vs2010, 4.0 vb.net, WinForms app calling AttemptLogin on a form load event.
I want to avoid blocking the form load if possible and I was hoping the tasks and continuation stuff in 4.0 would be the right way to go as I could run the main task on the default scheduler and the continuation on fromcurrentsynchronisationcontext but although I've got the OnAttemptLogin working I can't get my OnAttemptLoginCompleted function in the continuation to be called.
I think it's because the OnAttemptLogin returns a "RunToCompletion" task so the continuation never gets called. But I don't know how to deal with that, I've tried numerous things but I've now confused myself so much I'm pretty much mashing keys. Can anyone offer any advice? Am I simply doing it wrong or have I got the wrong idea all together?
Here's what I have so far, the OnAttemptLogin works as I would expect it to, but it then never calls the LongRunning tasks continuation.
Please note: I can't use await as I'm in vs2010 .net4.0 so I'm stuck with ContinueWith.
Public Sub AttemptLogin(OnAttemptLoginCompleted As Action(Of Task(Of HttpResponseMessage)))
Try
Dim LongRunningTask As Task(Of HttpResponseMessage) = Task.Factory.StartNew(Function()
Return OnAttemptLogin()
End Function, TaskScheduler.Default)
Dim UITask As Task(Of HttpResponseMessage) = LongRunningTask.ContinueWith(Sub(t)
OnAttemptLoginCompleted(t)
End Sub, TaskScheduler.FromCurrentSynchronizationContext)
LongRunningTask.Wait()
Catch ex As AggregateException
' nom nom nom
' do something useful
End Try
End Sub
Private Function OnAttemptLogin() As Task(Of HttpResponseMessage)
Dim aClient = New HttpClient()
Using (aClient)
' CREATE REQUEST
aClient.DefaultRequestHeaders.Accept.Add(New MediaTypeWithQualityHeaderValue("application/json"))
aClient.DefaultRequestHeaders.Add("Authorization", "Basic " + Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(String.Format("{0}:{1}", CallingDTO.Email, CallingDTO.Password))))
UserQueryDTO.UserName = UserDTO.Email
UserQueryDTO.Password = UserDTO.Password
Dim url As String = DnnRequest.GetUrl(Credentials.HttpAlias, cstModuleAssembly, "User", "CanLogin", False)
' POST REQUEST
Dim p As Task(Of HttpResponseMessage) = aClient.PostAsJsonAsync(url, UserQueryDTO).ContinueWith(Function(x)
' READ RESPONSE
Dim r = x.Result.Content.ReadAsAsync(Of HttpResponseMessage)()
r.Wait()
Return r.Result
End Function)
Try
p.Wait()
Catch ex As Exception
End Try
Return p
End Using
End Function

Answer 1

The problem here is ... convoluted. The main issue you have here, the reason why UITask won't run, is because LongRunningTask is not of type Task(Of HttpResponseMessage). It is actually a Task(Of Task(Of HttpResponseMessage)). OnAttempLogin() returns a Task(of H...), but the task that you start in form load is a Task that will return that Task, hence, Task(Of Task(Of ...)). So there's an exception in that line, hence the UITask line never runs. So the problem with the code is that there's too many Task things all over the place.
The other problem is that you aren't really doing anything asynchronously (except that part that never ran) since you are Wait()-ing for all the tasks. So you need to get rid of most of your waits to actually achieve that. Getting rid of the waits means you need to handle exceptions with a continuation.
Some minor points:
You don't really need the scheduler stuff, either.
UITask is simply a Task, not a Task(Of ...) since it doesn't return anything.
I'm continuing from UITask to handle exceptions so that it also catches UITask's exceptions. If I continued from LongRunningTask, I would miss those exceptions.
Below is an example of what I think the new code will look like. There may be a few syntax issues since I'm missing a few things to get this to compile:
Public Sub AttemptLogin(OnAttemptLoginCompleted As Action(Of Task(Of HttpResponseMessage)))
Dim LongRunningTask As Task(Of HttpResponseMessage) = OnAttemptLogin()
Dim UITask As Task = LongRunningTask.ContinueWith(AddressOf OnAttemptLoginCompleted)
uiTask.ContinueWith(Sub(t)
Dim ex As AggregateException = t.Exception
'nom nom nom
'all your exceptions will end up here.
End Sub, TaskContinuationOptions.OnlyOnFaulted)
End Sub
Private Function OnAttemptLogin() As Task(Of HttpResponseMessage)
Dim aClient = New HttpClient()
Using (aClient)
' CREATE REQUEST
aClient.DefaultRequestHeaders.Accept.Add(New MediaTypeWithQualityHeaderValue("application/json"))
aClient.DefaultRequestHeaders.Add("Authorization", "Basic " + Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(String.Format("{0}:{1}", CallingDTO.Email, CallingDTO.Password))))
UserQueryDTO.UserName = UserDTO.Email
UserQueryDTO.Password = UserDTO.Password
Dim url As String = DnnRequest.GetUrl(Credentials.HttpAlias, cstModuleAssembly, "User", "CanLogin", False)
' POST REQUEST
Dim p As Task(Of HttpResponseMessage) = aClient.PostAsJsonAsync(url, UserQueryDTO).ContinueWith(Function(x)
' READ RESPONSE
Dim r = x.Result.Content.ReadAsAsync(Of HttpResponseMessage)()
r.Wait()
Return r.Result
End Function)
Try
p.Wait()
Catch ex As Exception
End Try
Return p
End Using
End Function

Answer 2

my solution was to delete everything and give up, i will use something else, anything else, pff at this point ill lock the ui and not care, three days on this rubbish is crazy.
Marking jtseng's reply as correct even though it didnt work as hes the only reply and deserves something for taking the time to try and help.