ASCollectionNode

ASCollectionNode is equivalent to UIKit’s UICollectionView and can be used in place of any UICollectionView.

ASCollectionNode replaces UICollectionView’s required method

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath;
  

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
  

with your choice of one of the following methods

- (ASCellNode *)collectionNode:(ASCollectionNode *)collectionNode nodeForItemAtIndexPath:(NSIndexPath *)indexPath

override func collectionNode(_ collectionNode: ASCollectionNode, nodeForItemAt indexPath: IndexPath) -> ASCellNode
  

or

- (ASCellNodeBlock)collectionNode:(ASCollectionNode *)collectionNode nodeBlockForItemAtIndexPath:(NSIndexPath *)indexPath

override func collectionNode(_ collectionNode: ASCollectionNode, nodeBlockForItemAt indexPath: IndexPath) -> ASCellNodeBlock
  

It is recommended that you use the node block version of the method so that your collection node will be able to prepare and display all of its cells concurrently.

As noted in the previous section:

• ASCollectionNodes do not utilize cell reuse.
• Using the "nodeBlock" method is preferred.
• It is very important that the returned node blocks are thread-safe.
• ASCellNodes can be used by ASTableNode, ASCollectionNode and ASPagerNode.

Node Block Thread Safety Warning

It is very important that node blocks be thread-safe. One aspect of that is ensuring that the data model is accessed outside of the node block. Therefore, it is unlikely that you should need to use the index inside of the block.

Consider the following -collectionNode:nodeBlockForItemAtIndexPath: method.

- (ASCellNodeBlock)collectionNode:(ASCollectionNode *)collectionNode nodeBlockForItemAtIndexPath:(NSIndexPath *)indexPath
{
    PhotoModel *photoModel = [_photoFeed objectAtIndex:indexPath.row];
    
    // this may 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];
        cellNode.delegate = self;
        return cellNode;
    };
    
    return cellNodeBlock;
}
  

func collectionNode(_ collectionNode: ASCollectionNode, nodeBlockForItemAt indexPath: IndexPath) -> ASCellNodeBlock {
  guard photoFeed.count > indexPath.row else { return { ASCellNode() } }
    
  let photoModel = photoFeed[indexPath.row]
    
  // this may be executed on a background thread - it is important to make sure it is thread safe
  let cellNodeBlock = { () -> ASCellNode in
    let cellNode = PhotoCellNode(photo: photoModel)
    cellNode.delegate = self
    return cellNode
  }
    
  return cellNodeBlock
}

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

Replacing a UICollectionViewController with an ASDKViewController

Texture does not offer an equivalent to UICollectionViewController. Instead, you can use the flexibility of ASDKViewController to recreate any type of UI…ViewController.

Consider, the following ASDKViewController subclass.

An ASCollectionNode is assigned to be managed by an ASDKViewController in its -initWithNode: designated initializer method, thus making it a sort of ASCollectionNodeController.

- (instancetype)init
{
  _flowLayout = [[UICollectionViewFlowLayout alloc] init];
  _collectionNode = [[ASCollectionNode alloc] initWithCollectionViewLayout:_flowLayout];
  
  self = [super initWithNode:_collectionNode];
  if (self) {
    _flowLayout.minimumInteritemSpacing = 1;
    _flowLayout.minimumLineSpacing = 1;
  }
  
  return self;
}

init() {
  flowLayout = UICollectionViewFlowLayout()
  collectionNode = ASCollectionNode(collectionViewLayout: flowLayout)

  super.init(node: collectionNode)

  flowLayout.minimumInteritemSpacing = 1
  flowLayout.minimumLineSpacing = 1
}

This works just as well with any node including as an ASTableNode, ASPagerNode, etc.

Accessing the ASCollectionView

If you’ve used previous versions of Texture, you’ll notice that ASCollectionView has been removed in favor of ASCollectionNode.

The LocationCollectionNodeController above accesses the ASCollectionView directly in -viewDidLoad.

- (void)viewDidLoad
{
  [super viewDidLoad];
  
  _collectionNode.delegate = self;
  _collectionNode.dataSource = self;
  _collectionNode.view.allowsSelection = NO;
  _collectionNode.view.backgroundColor = [UIColor whiteColor];
}

override func viewDidLoad() {
  super.viewDidLoad()

  collectionNode.delegate = self
  collectionNode.dataSource = self
  collectionNode.view.allowsSelection = false
  collectionNode.view.backgroundColor = .white
}

Cell Sizing and Layout

As discussed in the previous section, ASCollectionNode and ASTableNode do not need to keep track of the height of their ASCellNodes.

Right now, cells will grow to fit their constrained size and will be laid out by whatever UICollectionViewLayout you provide.

You can also constrain cells used in a collection node using ASCollectionNode’s -constrainedSizeForItemAtIndexPath:.

Examples

The most detailed example of laying out the cells of an ASCollectionNode is the CustomCollectionView app. It includes a Pinterest style cell layout using an ASCollectionNode and a custom UICollectionViewLayout.

More Sample Apps with ASCollectionNodes

• ASDKgram
• CatDealsCollectionView
• ASCollectionView
• CustomCollectionView

Interoperability with UICollectionViewCells

ASCollectionNode supports using UICollectionViewCells alongside native ASCellNodes.

Note that these UIKit cells will not have the performance benefits of ASCellNodes (like preloading, async layout, and async drawing), even when mixed within the same ASCollectionNode.

However, this interoperability allows developers the flexibility to test out the framework without needing to convert all of their cells at once. Read more here.

Edit on GitHub