How to efficiently change ItemSource data while getting collected

Dear all,

I have a list box which is bind to a List of Product Categories with a maximum of 4 categories. Then when my user select one category I need to collect all product within that category. Then I am using the same list box and change the item source with new collected data ( this to avoid having an other items control to handle a new list querry, may be bad idea!)

For that on selected category item, I run following code from a ViewModel

private void ProcessSelectCategoryCommand(ListBox Container,RootCategoryViewModel cat)
        { 
        // we select a category and need to get list of product based on that category
            SelectedProductCategory = cat;
            Messenger.Default.Send<Message.OpenProductList>(new Message.OpenProductList(this,Container,true));
            //call asynchronously the product summary information from slelected category of product
            Task.Factory.StartNew(() =>
            {
                GetProductSummaryData(SelectedProductCategory, ViewModelLocator.MainViewModelStatic.StoreInfoViewModel.StoreId);
            }).ContinueWith(task =>
            {
                if (task.IsFaulted)
                {
                    Exception ex = task.Exception;
                    log.Debug("Task Faulted <ProcessSelectCategoryCommand>", ex.InnerException);
                }
                else
                {
                    ProductListReady = true;
                    IsCategoryListVisible = false;
                    Application.Current.Dispatcher.BeginInvoke(DispatcherPriority.Background, new Action(() =>
                    {
                        if (ProductSummaryItems != null)
                        {
                            //ICollectionView view = CollectionViewSource.GetDefaultView(ProductSummaryItems);
                            //view.GroupDescriptions.Add(new PropertyGroupDescription("SubCatgoryName"));
                            //view.SortDescriptions.Add(new SortDescription("SubCatgoryName", ListSortDirection.Ascending));
                            Container.ItemsSource = ProductSummaryItems;
                        }
                        else Container.ItemsSource = null;
                    }));

                }

            });

        }

What is weird in that, in order to not show to user the change of data for the same list box, I hide the list box then change the itemSource and then show the list box. I am doing this in order to avoid seeing to user sundenly change of data which is not so user friendly in user experience.

Do you see a better smoother approach for doing this ?

Does the fact of handling single Listbox in that case is suitable or better to go with separate controls?

thnks for advise

regards