WinRT FlipView binding fails possibly

Question

I have a xaml page:

<Page x:Class="DailyStyleW8.MainPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:local="using:DailyStyleW8"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:converters="using:DataTypes"
      mc:Ignorable="d">

  <Page.Resources>
    <converters:PortableImageConverter x:Key="ImageConverter" />
  </Page.Resources>

  <Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
    <Grid>
      <ProgressBar x:Name="loadingViewer"
                   IsIndeterminate="True"
                   Height="20" />
      <FlipView x:Name="displayViewer"
                ItemsSource="{Binding}"
                Visibility="Collapsed">
        <FlipView.ItemTemplate>
          <DataTemplate>
            <Grid>
              <Image Source="{Binding Image,Converter={StaticResource ImageConverter}}" />
              <TextBlock Text="{Binding Name}" />
            </Grid>
          </DataTemplate>
        </FlipView.ItemTemplate>
      </FlipView>
    </Grid>
  </Grid>
</Page>

and in the code behind file:

using DailyStyleApp;
using PortableAPI;
using System;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Navigation;

namespace DailyStyleW8
{
    /// <summary>
    /// Display a list of recent updates to the user
    /// </summary>
    public sealed partial class MainPage : Page
    {
        Controller controller = new Controller();

        public MainPage()
        {
            this.InitializeComponent();
        }

        /// <summary>
        /// Invoked when this page is about to be displayed in a Frame.
        /// </summary>
        /// <param name="e">Event data that describes how this page was reached.  The Parameter
        /// property is typically used to configure the page.</param>
        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
            LoadContent();
        }

        private async void LoadContent()
        {
            var viewModel = await controller.GetMultiDayAsync(DateTime.Now, PortableAPIProvider.Storage.ReadFromSettings<int>("CacheDuration", 7));
            displayViewer.ItemsSource = viewModel.Items;
            displayViewer.Visibility = Windows.UI.Xaml.Visibility.Visible;
            loadingViewer.Visibility = Windows.UI.Xaml.Visibility.Collapsed;
        }
    }
}

Now when I run the code the LoadContent function is called correctly and the viewModel object is formed correctly. If I comment out the line displayViewer.ItemsSource = viewModel.Items; the ProgressBar visibility is changed as you would expect.

When that line is left in and stepped through all 4 lines inside the LoadContent method are run, however the FlipView is not updated with the new items and the ProgressBar visibility is not changed. viewModel.Items is of type List<T>.

I am even sure really what to be searching for here. I am guessing it's something wrong with the XAML and my binding?

Answer 1

The issue related to this question was actually to do with another section of code in the application. Elsewhere I had a series of async / await calls that were locking up the UI thread.

This prevented the scheduler from ever triggering the callbacks for the async. In short solution to the problem: Never call await on something that is called from the UI thread (and not via another async call).