test.cs

[XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class PickerListCell
    {
        public PickerListCell()
        {
            InitializeComponent();

            MyPicker.Unfocused += MyPicker_Unfocused;
        }

        private void MyPicker_Unfocused(object sender, FocusEventArgs e)
        {
            _pickerListViewModel.ResetPicker();
            ForceUpdateSize();
        }

        private void TapGestureRecognizer_OnTapped(object sender, EventArgs e)
        {
            MyPicker.Focus();
        }

        private PickerListFieldViewModel _pickerListViewModel;

        protected override void OnBindingContextChanged()
        {
            base.OnBindingContextChanged();

            if (BindingContext != null)
            {
                _pickerListViewModel = (PickerListFieldViewModel)BindingContext;

                _pickerListViewModel.SelectedItems.CollectionChanged += SelectedItemsOnCollectionChanged;
            }
        }

        private void SelectedItemsOnCollectionChanged(object sender, NotifyCollectionChangedEventArgs notifyCollectionChangedEventArgs)
        {
            //MessagingCenter.Send(_pickerListViewModel, "ForceLayout");
        }

        protected override void OnDisappearing()
        {
            _pickerListViewModel.SelectedItems.CollectionChanged -= SelectedItemsOnCollectionChanged;
        }
    }