How do I redraw UICollectionView when MvxCollectionViewSource's data changes? - data-binding

Question

I am using Xamarin and MVVMCross to implement an IOS app. A view I'm working on is displaying correctly, but ONLY when I hard-code the data being bound to inside my ViewModel and NOT when (as by design and necessity) my data arrives late from SQLite, only an indeterminate time after the view is shown.
What I am using and accomplished so far:
Working/Showing storyboard for my View that has a UICollectionView
inside (called: CollectionView in code below)
Custom layout and XIB file for every UICollectionViewCell that also displays correctly in my view
A view that works and displays correctly only if ViewModel data is fully populated the moment ViewDidLoad() is called.
Problem:
My data in my ViewModel is updated by the Model's databases in an uncertain amount of time whilst the view is happily being shown. When I bind the data as shown below (and trying two-way/one-way bindings and the like as well), I don't get updates on my view as the final data comes in later.
What I can't seem to do:
Redraw the UICollectionView or maybe refresh the
MvxCollectionViewSource below to ensure that as the ViewModel's data changes, I can actually redraw the UICollectionView and show my
custom cells with new and updated data.
THE CODE(TM)
The CollectionView cells are implemented as follows. I followed all examples online and from that Stuart Bloke and his Kittens to make sure I implement all the patterns exactly the same:
[Register("MyCell")]
public partial class MyCell : MvxCollectionViewCell
{
public static readonly UINib Nib = UINib.FromName("MyCell", NSBundle.MainBundle);
public static readonly NSString Key = new NSString("MyCell");
public MyCell(IntPtr handle) : base(handle)
{
this.DelayBind(() => {
var set = this.CreateBindingSet<MyCell, SomeModelClass>();
set.Bind(Label1).To(item => item.Label1);
set.Bind(Label2).To(item => item.Label2);
set.Apply();
});
}
public static MyCell Create()
{
return (MyCell)Nib.Instantiate(null, null)[0];
}
}
My ViewDidLoad() in the View looks something like this:
CollectionView.RegisterNibForCell(MyCell.Nib, MyCell.Key);
var source = new MvxCollectionViewSource(CollectionView, MyCell.Key);
CollectionView.Source = source;
var set = this.CreateBindingSet<MyView, MyViewModel>();
set.Bind(source).To(vm => vm.ListOfStuff);
set.Apply();
CollectionView.ReloadData();
NB! The ListOfStuff shown above is really just a List of a custom class containing 2 strings right now.
TL:DR: I don't know ListOfStuff's values the moment I call the above code. When I hard-code them in the ViewModel, I get joy. If I don't, I don't, even as data gets updated correctly later.
I now reach out to you, the neurons of the brain of crowdsourcing...

Answer 1

Instead of using a List<T> use ObservableCollection<T> and new items should be added to the CollectionView.
The UI needs to know when the collection has changed. ObservableCollection<T> implements INotifyCollectionChanged and INotifyPropertyChanged and communicates with the UI when the collection changes.
You shouldn't need ReloadData() anymore if you're using ObservableCollection<T>.
This extension method might be of use when adding range of IEnumerable<T>
public static class ObservableCollectionExtensionMethod
{
public static void AddRange<TSource>(this ObservableCollection<TSource> source, IEnumerable<TSource> collection)
{
foreach (var i in collection) source.Add(i);
}
}