Generic item data model.
        public ItemViewModel(IScreen hostScreen, SampleDataItem sampleDataItem)
        {
            HostScreen = hostScreen;
            _sampleDataItem = sampleDataItem;

            this.WhenNavigatedTo(() =>
                {
                    SetItem();
                    return null;
                });
        }
 private async void SetItem()
 {
     Item = await SampleDataSource.GetItemAsync(_sampleDataItem.UniqueId);
 }