ASPagerNode

ASPagerNode is a subclass of ASCollectionNode with a specific UICollectionViewLayout used under the hood.

Using it allows you to produce a page style UI similar to what you’d create with UIKit’s UIPageViewController. ASPagerNode 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

func numberOfPages(in pagerNode: ASPagerNode) -> Int

and

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

func pagerNode(_ pagerNode: ASPagerNode, nodeAt index: Int) -> ASCellNode

or

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

func pagerNode(_ pagerNode: ASPagerNode, nodeBlockAt index: Int) -> ASCellNodeBlock

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

Note that neither methods should rely on cell reuse (they will be called once per row). Also, 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 the -init: method of each of your subnodes will be 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[index];
  
  // this part can be executed on a background thread - it is important to make sure it is thread safe!
  ASCellNode *(^cellNodeBlock)() = ^ASCellNode *() {
    PhotoCellNode *cellNode = [[PhotoCellNode alloc] initWithPhoto:photoModel];
    return cellNode;
  };
  
  return cellNodeBlock;
}

func pagerNode(_ pagerNode: ASPagerNode, nodeBlockAt index: Int) -> ASCellNodeBlock {
    guard photoFeed.count > index else { return { ASCellNode() } }
    
    let photoModel = photoFeed[index]
    let cellNodeBlock = { () -> ASCellNode in
        let cellNode = PhotoCellNode(photo: photoModel)
        return cellNode
    }
    return cellNodeBlock
}

Using an ASDKViewController For Optimal Performance

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

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

func pagerNode(_ pagerNode: ASPagerNode, nodeAt index: Int) -> ASCellNode {
    guard animals.count > index else { return ASCellNode() }

    let animal = animals[index]
    let node = ASCellNode(viewControllerBlock: { () -> UIViewController in
      return AnimalTableNodeController(animals: animals)
    }, didLoadBlock: nil)

    node.style.preferredSize = pagerNode.bounds.size

    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 style.preferredSize so that it can be laid out correctly.

Use ASPagerNode as root node of an ASDKViewController

Log message while popping back in the view controller hierarchy

If you use an ASPagerNode embedded in an ASDKViewController in full screen. If you pop back from the view controller hierarchy you will see some error message in the console.

To resolve the error message set self.automaticallyAdjustsScrollViewInsets = NO; in viewDidLoad in your ASDKViewController subclass.

navigationBar.translucent is set to YES

If you have an ASPagerNode embedded in an ASDKViewController in full screen and set the navigationBar.translucent to YES, you will see an error message while pushing the view controller on the view controller stack.

To resolve the error message add [self.pagerNode waitUntilAllUpdatesAreCommitted]; within - (void)viewWillAppear:(BOOL)animated in your ASDKViewController subclass. Unfortunately the disadvantage of this is that the first measurement pass will block the main thread until it finishes.

Some more details about the error messages above

The reason for this error message is that due to the asynchronous nature of Texture, measurement of nodes will happen on a background thread as UIKit will resize the view of the ASDKViewController on on the main thread. The new layout pass has to wait until the old layout pass finishes with an old layout constrained size. Unfortunately while the measurement pass with the old constrained size is still in progress the ASPagerFlowLayout that is backing a ASPagerNode will print some errors in the console as it expects sizes for nodes already measured with the new constrained size.

Sample Apps

Check out the following sample apps to see an ASPagerNode in action:

• PagerNode
• VerticalWithinHorizontalScrolling

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