Question

I’m building a Windows 8 Store app and I’m having trouble with a CollectionViewSource claiming that the collection it is returning has zero items when async is involved.

In my ViewModel I have the following code (note some stuff is missing to make this a bit more simple to explain)

public MainViewModel(IFileRepository fileRepository)
{
   items = new CollectionViewSource();
   _fileRepository = fileRepository;
   this.Construct();
   items.Source = new ObservableCollection<FileViewModel>(Files);
}

private async void Construct()
{
   Files = new ObservableCollection<FileViewModel>();
   IList _files = await _fileRepository.GetFiles();
   foreach (File file in _files)
   {
      Files.Add(new FileViewModel(file));
   }
}

private CollectionViewSource items;
public ICollectionView Items
{
    get
    {
        return items.View;
    }
}

And then in the XAML I’m binding a GridView’s ItemsSource to Items and I have all the relevant DataTemplates in place to display the data.

My issue is that, because of the async fetch of the files, my Items collection returns empty and the View presents no data.

If I remove the async call and create a mock collection of File objects inline, the code works as expected.

Can anybody suggest a way around this? In WPF I would attempt to create a Boolean isBusy property for when the collection is loading, but that feels like a wrong thing to do with this new async stuff.

Any pointers would be great!

Kris

Answer 1

As it stands, when you create the ObservableCollection for the Source, Files is empty since you started Construct, but didn’t (a)wait for it to finish.

I would avoid the second ‘wrapper’ ObservableCollection and set Source = Files, so when the Construct code writes to Files, it’ll be observed by the CollectionViewSource (which is likely your actual intent)