WPF How to set a maximum amount of results from CollectionViewSource

Question

I am trying to display a set of data using a DataTemplate in a ItemsControl, with the ItemsPanel set as a uniform grid of size 3 x 3. The ItemsSource of the ItemsControl is set to bind to a CollectionViewSource which filters the source collection based on a search term. This all works fine.

The list I am binding to is of an arbitrary size, but I only want 9 results to be displayed, but I can't for the life of me work out how to either
a) limit the CollectionViewSource to output the first 9 items
b) limit the UniformPanel to only 3 x 3 and never to create new rows
c) limit the ItemsControl to only allow 9 data templates to be created at once.

I'm really scratching my head because I'm sure this is a common databinding scenario but I can't find anything on the web about it.

Answer 1

This is just one of those things you can't do in XAML (yet).

You could create a "CollectionViewSourceView" (:P), which will be updated whenever CollectionViewSource is updated, to only output the first 9 items. Still, this is going into the codebehind (or better, the viewmodel).

Answer 2

Two solutions I can think of:

If you are using View Model, put the logic in there to create a property that you can bind to that only ever has 9 elements. Make sure it's unit tested to ensure more than 9 elements never sneak into the collection.

Alternatively you could use a converter when binding the items source to convert the full list to a reduced list of the first 9.

Answer 3

I was about to say the same as James Hay (use a Converter), but I would also add that you can databind a ConverterParameter in the XAML to dynamically specify how many items are returned.