#BookBrowser

Endless Scrolling UICollectionView with CoreData

Demonstrates the use of a UICollectionView that is backed by CoreData and which allows for endless scrolling i.e. loads more items when reaching the bottom of the UICollectionView. The application interacts with a RESTful API to download a number of books. These books are cached within CoreData for viewing on initial load and whenever the API or user is offline.

###Endless Scrolling

The scrolling of the UICollectionView is tracked, and whenever it reaches the bottom an API request is made to load more books. If the API fails, more items are loaded via CoreData.

###API Interactions The BookEngine class provides the interfaces to the API. Contains two main methods:

- (NSURLSessionDataTask *) booksForCategory:(NSString *)categoryID
                     page:(NSUInteger)page
                    count:(NSUInteger)count
          completionBlock:(void(^)(NSArray *books))completionBlock
               errorBlock:(void(^)(NSError *error))errorBlock;

this method gets books for a certain categoryID adjusted by the page and count parameters. Responses are passed back via blocks.

- (NSURLSessionDataTask *) booksForCategory:(NSString *)categoryID
          completionBlock:(void(^)(NSArray *books))completionBlock
               errorBlock:(void(^)(NSError *error))errorBlock;

this second method gets books for a certain categoryID using default page and count parameters.

##CoreData

For the sake of this assignment, our model contains 2 entities: Book and Author. An important attribute within the Book entity is called pageID which is used to map a book to a certain page. This is useful when loading more books from our cache. Another important attribute is the localOrderIndex which is used to order books of the same page.. this was used so that the order of the books matches the order they were fetched at from the API. This provides a better experience as users will not get a different order each time. Both attributes are used within our sort descriptors and predicates.