AsyncDisplayKit/_docs/containers-aspagernode.md

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ASPagerNode is a subclass of ASCollectionNode.

Using it allows you to produce a page style UI similar to what you'd create with UIKit's UIPageViewController. ASPager node currently supports staying on the correct page during rotation. It does not currently support circular scrolling.

The main dataSource methods are:

- (NSInteger)numberOfPagesInPagerNode:(ASPagerNode *)pagerNode

and

- (ASCellNode *)pagerNode:(ASPagerNode *)pagerNode nodeAtIndex:(NSInteger)index

or

- (ASCellNodeBlock)pagerNode:(ASPagerNode *)pagerNode nodeBlockAtIndex:(NSInteger)index (recommended)

These two methods, just as with ASCollectionNode and ASTableNode need to return either an ASCellNode or an ASCellNodeBlock - a block that creates a ASCellNode which can be run on a background thread.

Note that both of these methods should not implement reuse (they will be called once per row). Unlike UIKit, these methods are not called when the row is just about to display.

While pagerNode:nodeAtIndex: will be called on the main thread, pagerNode:nodeBlockAtIndex: is preferred because it concurrently allocates cell nodes, meaning that all of the init: methods for all of your subnodes are run in the background. It is very important that node blocks be thread-safe as they can be called on the main thread or a background queue.

##Node Block Thread Safety Warning##

It is imperative that the data model be accessed outside of the node block. This means that it is highly unlikely that you should need to use the index inside of the block.

In the example below, you can see how the index is used to access the photo model before creating the node block.

- (ASCellNodeBlock)pagerNode:(ASPagerNode *)pagerNode nodeBlockAtIndex:(NSInteger)index
{
  PhotoModel *photoModel = [_photoFeed objectAtIndex:index];
  
  // this part can be executed on a background thread - it is important to make sure it is thread safe!
  ASCellNode *(^ASCellNodeBlock)() = ^ASCellNode *() {
    PhotoCellNode *cellNode = [[PhotoCellNode alloc] initWithPhotoObject:photoModel];
    return cellNode;
  };
  
  return ASCellNodeBlock;
}

##Use ASViewControllers For Optimal Performance##

One especially useful pattern is to return an ASCellNode that is initialized with an existing UIViewController or ASViewController. For optimal performance, use an ASViewController.

- (ASCellNode *)pagerNode:(ASPagerNode *)pagerNode nodeAtIndex:(NSInteger)index
{
    CGSize pagerNodeSize = pagerNode.bounds.size;
    NSArray *animals = self.animals[index];
    
    ASCellNode *node = [[ASCellNode alloc] initWithViewControllerBlock:^{
        return [[AnimalTableNodeController alloc] initWithAnimals:animals];;
    } didLoadBlock:nil];
    
    node.preferredFrameSize = pagerNodeSize;
    
    return node;
}

In this example, you can see that the node is constructed using the -initWithViewControllerBlock: method. It is usually necessary to provide a cell created this way with a preferredFrameSize so that it can be laid out correctly.

##Sample Apps##

Check out the following sample apps to see an ASPagerNode implemented within an app:

• PagerNode
• VerticalWithinHorizontalScrolling