ItemsCollection's ContainerFromItem fails for an object that I'm pretty sure is in the collection

Question

I am trying to add search functionality to a ListBox that will scroll down to the item being searched for.

I have a ListBox that is bound to an ObservableCollection that I have filled with a bunch of RecipeNameDTO objects. I can easily find an object in the Items collection with a simple search.

string searchItem = tbSearchString.Text;
var recipenameitem = lbRecipeNames.Items.Cast<DTO.RecipeNameDTO>().Where(u => u.RecipeName.ToLower().Contains(searchItem.ToLower())).FirstOrDefault();

I can reproducibly find items with this method.

However, if I then try to find the object's container using ContainerFromItem, the method returns a null unless the object is visible in the ListBox when I execute the method:

ListBoxItem lbi = (ListBoxItem)lbRecipeNames.ItemContainerGenerator.ContainerFromItem(recipenameitem);

I am certain (I think) that the actual object exists in the ItemsCollection before I execute ContainerFromItem because I use a non null result from the search I documented in the beginning of this post. Also, I can scroll down the ListBox and find the object I'm searching for.

It must be something with the way the ListBox caches the objects in the ItemsCollection that is preventing ContainerFromItem from returning the container. Is there a fix to my code (or understanding of the problem)?

Michael

Answer 1

I took Andy's suggestion and made my ListBox IsSynchronizedWithCurrent = True and then used the following code to set the current item and scroll it into view:

    string searchItem = tbSearchString.Text;

    CollectionViewSource cvs = (CollectionViewSource)this.FindResource("cvsRecipeName");
    ObservableCollection<DTO.RecipeNameDTO> itemsCollection = (ObservableCollection<DTO.RecipeNameDTO>)cvs.Source;

    List<DTO.RecipeNameDTO> recipenameitems = itemsCollection.Where(u => u.RecipeName.ToLower().Contains(searchItem.ToLower())).ToList();
    if (recipenameitems.Count > 0) { cvs.View.MoveCurrentTo(recipenameitems[0]);}

    lbRecipeNames.ScrollIntoView(lbRecipeNames.SelectedItem);

I'm sure I could modify this to make it more flexible, but here's the first fix.