Diffable datasource storage.md

ProxyDiffableDataSourceStorage

ProxyDiffableDataSourceStorage is a proxy class used by DTTableViewManager/DTCollectionViewManager frameworks to support diffable datasources in iOS 13.

All it does, it contain wrapper closures, that redirect datasource questions to diffable datasource object. Additionally, It has the same supplementary model provider logic that all storages have.

Example

You can find working example of diffable datasources integration here.

Benefits of using ProxyDiffableDataSourceStorage

For one, this implementation allows you to use diffable datasources with DTCollectionViewManager and DTTableViewManager. Secondly, it simplifies a lot of setup with diffable datasources.

// Without `DTCollectionViewManager` and `ProxyDiffableDataSourceStorage`
dataSource = UICollectionViewDiffableDataSource
    <Section, MountainsController.Mountain>(collectionView: mountainsCollectionView) {
        (collectionView: UICollectionView, indexPath: IndexPath,
        mountain: MountainsController.Mountain) -> UICollectionViewCell? in
    guard let mountainCell = collectionView.dequeueReusableCell(
        withReuseIdentifier: LabelCell.reuseIdentifier, for: indexPath) as? LabelCell else {
            fatalError("Cannot create new cell") }
    mountainCell.label.text = mountain.name
    return mountainCell
}

into:

// With `DTCollectionViewManager` and `ProxyDiffableDataSourceStorage`
dataSource = manager.configureDiffableDataSource { indexPath, model in
   model
}

Basically instead of managing cells, you only manage models, because DTTableViewManager and DTCollectionViewManager already manage cells for you.

Another small benefit for UITableView users is that diffable datasources for UITableView do not support headers or footers, but when using ProxyDiffableDataSourceStorage - they work perfectly fine, powered by supplementaryModelProvider.

Please note, that due to underlying implementation details, using UICollectionViewDiffableDataSource.supplementaryViewProvider property is not supported. Please use ProxyDiffableDataSourceStorage.supplementaryModelProvider property instead.