This version of the app shows how you would manage a more complex scenario with the usage of Streams and BLoC (business logic components).

This app has the following functionality on top of the ones in other versions:

• The product list is arbitrarily large (in fact, it is infinite).
• Products are loaded asynchronously from (fake) network in batches.
• Only a limited slice of the product catalog is held in memory.
• Products in the catalog that are already in cart are marked as such (their name is underlined).

To make this work, we're introducing two new BLoCs:

• CatalogBloc, which takes care of loading data from network according to the latest indexes in the infinite product grid
• ProductSquareBloc, which tracks whether a product is already in cart or not

The concept of BLoC is lightly touched on in our I/O session (for which this is the companion sample repository) and more thoroughly explained in this DartConf talk by Paolo Soares.