I'm using mvvmcross and xamarin to bind an ObservableCollection to a UITableView. The collection is updated in place using the Add, Remove and Move methods. These calls correctly trigger INotifyCollectionChanged events and the TableView is updated as expected the first time the view containing the table is shown. If the user navigates away from the original view as part of the normal application flow but later returns the correct data is loaded into the table but calls to add, move and remove no longer update the table.
- The INotifyCollectionChanged events are still being fired when the collection is updated
- If I manually subscribe to these events in my subclass of MvxStandardTableViewSource and try and call ReloadData on the UITableView still does not update
- My presenter is creating a new instance of the viewmodel and view each time the page is visited.
I'm also using Xamarin-Sidebar (https://components.xamarin.com/view/sidebarnavigation) for navigation in my application with a custom presenter to load the views but as far as I can tell the view is initialised via exactly the same code path whether it's the first or subsequent visit.
My presenters Show() method looks like this:
public override void Show(MvxViewModelRequest request)
{
if (request.PresentationValues != null)
{
if(NavigationFactory.CheckNavigationMode(request.PresentationValues, NavigationFactory.ClearStack))
{
MasterNavigationController.ViewControllers = new UIViewController[0];
base.Show(request);
}
else if(NavigationFactory.CheckNavigationMode(request.PresentationValues, NavigationFactory.LoadView))
{
var root = MasterNavigationController.TopViewController as RootViewController;
var view = this.CreateViewControllerFor(request) as UIViewController;
root.SidebarController.ChangeContentView(view);
}
}
else
{
base.Show(request);
}
}
The binding in my ViewController looks like this:
public override void ViewDidLoad()
{
base.ViewDidLoad();
View.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight;
var source = new TracksTableSource(TableView, "TitleText Title; ImageUrl ImageUrl", ViewModel);
TableView.Source = source;
var set = this.CreateBindingSet<TracksViewController, TracksViewModel>();
set.Bind(source).To(vm => vm.PlaylistTable);
set.Apply();
}
And my viewmodel is as below where PlaylistTable is a subclass of ObservableCollection with the Update method using add, move and remove to keep the collection up to date.
public class TracksViewModel : MvxViewModel
{
private readonly IPlaylistService _playlistService;
private readonly IMessengerService _messengerService;
private readonly MvxSubscriptionToken _playlistToken;
public PlaylistTable PlaylistTable { get; set; }
public TracksViewModel(IPlaylistService playlistService, IMessengerService messengerService)
{
_playlistService = playlistService;
_messengerService = messengerService;
if (!messengerService.IsSubscribed<PlaylistUpdateMessage>(GetType().Name))
_playlistToken = _messengerService.Subscribe<PlaylistUpdateMessage>(OnDirtyPlaylist, GetType().Name);
}
public void Init(NavigationParameters parameters)
{
PlaylistTable = new PlaylistTable(parameters.PlaylistId);
UpdatePlaylist(parameters.PlaylistId);
}
public async void UpdatePlaylist(Guid playlistId)
{
var response = await _playlistService.Get(playlistId);
PlaylistTable.Update(new Playlist(response));
}
private void OnDirtyPlaylist(PlaylistUpdateMessage message)
{
UpdatePlaylist(message.PlaylistId);
}
}
This setup works perfectly the first time the view is initialised and updates the table correctly, it's only the second and subsequent times the view is initialised that the table fails to update. Can anyone explain why the binding fails when it appears the view is created using the same techniques in both instances?
I can post additional code if required but I believe the issue will be how I'm using the presenter since the code I've not posted from PlaylistTable functions correctly in unit tests and on first viewing.
