Conversion - 'Result' is not a member of 'System.Threading.Tasks.Task'

Question

Using VS 2010, VB.NET, HTTPClient, .NET 4.0, and Windows Forms.

I am trying to get a windows application to consume JSON coming from a Web API that I have created. Web API works great and I can view the results from a browser. Found this article that I have been trying to get working only using VB.NET instead of C#. http://www.asp.net/web-api/overview/web-api-clients/calling-a-web-api-from-a-wpf-application

The critical part of the code is this function:

private void GetProducts(object sender, RoutedEventArgs e)
{
btnGetProducts.IsEnabled = false;

client.GetAsync("api/products/2").ContinueWith((t) =>
{
    if (t.IsFaulted)
    {
        MessageBox.Show(t.Exception.Message);
        btnGetProducts.IsEnabled = true;
    }
    else
    {
        var response = t.Result;
        if (response.IsSuccessStatusCode)
        {
            response.Content.ReadAsAsync<IEnumerable<Product>>().
                ContinueWith(t2 =>
                    {
                        if (t2.IsFaulted)
                        {
                            MessageBox.Show(t2.Exception.Message);
                            btnGetProducts.IsEnabled = true;
                        }
                        else
                        {
                            var products = t2.Result;
                            _products.CopyFrom(products);
                            btnGetProducts.IsEnabled = true;
                        }
                    }, TaskScheduler.FromCurrentSynchronizationContext());
        }

    }
}, TaskScheduler.FromCurrentSynchronizationContext());
}

I have tried to convert this to VB.NET but I am having issues with the t.Result saying "'Result' is not a member of 'System.Threading.Tasks.Task'."

Here is my attempt to convert it to VB.NET:

Private Sub GetProducts(sender As Object, e As RoutedEventArgs)
    btnGetProducts.IsEnabled = False

    client.GetAsync("api/products/2") _
        .ContinueWith(Of HttpResponseMessage) _
        (Function(t)
             If t.IsFaulted Then
                 MessageBox.Show(t.Exception.Message)
                 btnGetProducts.IsEnabled = True
             Else

                 '***************************************************************
                 Dim response = t.Result 'This is the line that is giving me grief. Error Msg: 'Result' is not a member of 'System.Threading.Tasks.Task'.
                 '***************************************************************

                 If response.IsSuccessStatusCode Then
                     response.Content.ReadAsAsync(Of IEnumerable(Of SendNotice)).ContinueWith _
                         (Function(t2)
                              If t2.IsFaulted Then
                                  MessageBox.Show(t2.Exception.Message)
                                  btnGetProducts.IsEnabled = True
                              Else
                                  Dim products = t2.Result
                                  _lstSN.CopyFrom(products)
                                  btnGetProducts.IsEnabled = True
                              End If

                          End Function, TaskScheduler.FromCurrentSynchronizationContext())

                 End If
             End If

         End Function, TaskScheduler.FromCurrentSynchronizationContext())
End Sub

Any idea why I am getting this error and what am I missing in my code to allow me to catch the returning JSON data?

Thanks!

Answer 1

This is because VB.NET type inference is not great in Visual Studio 2010. You'll need to give the compiler a bit of extra help by specifying the actual type returned by your client.GetAsync(), like so:

client _
   .GetAsync("api/products/2") _
   .ContinueWith( _
       Sub(t As Task(Of HttpResponseMessage))
           ...
       End Sub, _
       TaskScheduler.FromCurrentSynchronizationContext())

Note: I've changed your Function to Sub because I didn't see any Return statements.

Answer 2

Try this:

client.GetAsync("api/products/2") _
        .ContinueWith(Sub(t)
                       If t.IsFaulted Then
                       .
                       .
                       .

Answer 3

Try changing your lambda from a Function to a Sub.