Changing content of MvxPickerViewModel - xamarin.ios

Question

I am writing a simple application that contains a database of items. The items have a type, manufacturer, model, and a few other properties. I have a implemented three UIPickerView's with MvxPickerViewModel's as outlined in N=19 of the N+1 series for MvvmCross. There is one UIPickerView/MvxPickerViewModel for each the type, the manufacturer, and the model (only one is ever on the screen at a time). However if I update the ItemSource data for a MvxPickerViewModel, the rows that were already visible in the UIPickerView do not refresh until they are scrolled off the screen. The N=19 example, does not update the list of items in the UIPickerView so it isn't clear that the problem didn't exist there. Have I made a mistake or has anyone else experienced this? Is there a work around?
public override void ViewDidLoad ()
{
base.ViewDidLoad ();
NavigationController.NavigationBarHidden = true;
var comparableTableViewSource = new MvxStandardTableViewSource(ComparableLV);
ComparableLV.Source = comparableTableViewSource;
var ManufacturerPicker = new UIPickerView();
var manufacturerPickerModel = new MvxPickerViewModel(ManufacturerPicker);
ManufacturerPicker.Model = manufacturerPickerModel;
ManufacturerPicker.ShowSelectionIndicator = true;
ManufacturerTextField.InputView = ManufacturerPicker;
var ModelPicker = new UIPickerView();
var modelPickerModel = new MvxPickerViewModel(ModelPicker);
ModelPicker.Model = modelPickerModel;
ModelPicker.ShowSelectionIndicator = true;
ModelTextField.InputView = ModelPicker;
var TypePicker = new UIPickerView();
var typePickerModel = new MvxPickerViewModel(TypePicker);
TypePicker.Model = typePickerModel;
TypePicker.ShowSelectionIndicator = true;
TypeTextField.InputView = TypePicker;
var set = this.CreateBindingSet<FirstView, FirstViewModel>();
set.Bind(comparableTableViewSource).For(s => s.ItemsSource).To(vm => vm.Comparables);
set.Bind(manufacturerPickerModel).For(p => p.ItemsSource).To(vm => vm.Manufacturers);
set.Bind(manufacturerPickerModel).For(p => p.SelectedItem).To(vm => vm.SelectedManufacturer);
set.Bind(ManufacturerTextField).To(vm => vm.SelectedManufacturer);
set.Bind(modelPickerModel).For(p => p.ItemsSource).To(vm => vm.Models);
set.Bind(modelPickerModel).For(p => p.SelectedItem).To(vm => vm.SelectedModel);
set.Bind(ModelTextField).To(vm => vm.SelectedModel);
set.Bind(typePickerModel).For(p => p.ItemsSource).To(vm => vm.Types);
set.Bind(typePickerModel).For(p => p.SelectedItem).To(vm => vm.SelectedType);
set.Bind(TypeTextField).To(vm => vm.SelectedType);
set.Apply();
var g = new UITapGestureRecognizer(() => {
HornTextField.ResignFirstResponder();
ManufacturerTextField.ResignFirstResponder();
ModelTextField.ResignFirstResponder();
});
View.AddGestureRecognizer(g);
}

Answer 1

Looking at MvxPickerViewModel.cs I'm suspicious that there is no call to ReloadAllComponents (or to ReloadComponent[0]) when the ItemsSource itself changes, but there is a call when the Collection internally changes.
As a workaround, perhaps try a subclass like:
public class MyPickerViewModel
: MvxPickerViewModel
{
private readonly UIPickerView _pickerView;
public MyPickerViewModel(UIPickerView pickerView)
: base(pickerViww)
{
_pickerView = pickerView;
}
[MvxSetToNullAfterBinding]
public override IEnumerable ItemsSource
{
get { return base.ItemsSource; }
set
{
base.ItemsSource = value;
if (value != null)
_pcikerView.ReloadComponent(0);
}
}
}
Would also be great to get a fix back into MvvmCross...