Merge pull request #3 from alexjameslittle/master

SupplementaryViewFactory for section headers and footers

Author: icanzilb

Sources/CombineDataSources/CollectionView/CollectionViewItemsController.swift

@@ -18,6 +18,7 @@ public class CollectionViewItemsController<CollectionType>: NSObject, UICollecti
 
   public typealias Element = CollectionType.Element.Element
   public typealias CellFactory<Element: Equatable> = (CollectionViewItemsController<CollectionType>, UICollectionView, IndexPath, Element) -> UICollectionViewCell
+  public typealias SupplementaryViewFactory = (CollectionViewItemsController<CollectionType>, UICollectionView, String, IndexPath, CollectionType.Element) -> UICollectionReusableView
   public typealias CellConfig<Element, Cell> = (Cell, IndexPath, Element) -> Void
 
   private let cellFactory: CellFactory<Element>
@@ -31,6 +32,8 @@ public class CollectionViewItemsController<CollectionType>: NSObject, UICollecti
 
   /// A fallback data source to implement custom logic like indexes, dragging, etc.
   public var dataSource: UICollectionViewDataSource?
+
+  public var configureSupplementaryView: SupplementaryViewFactory?
 
   // MARK: - Init
 
@@ -97,6 +100,13 @@ public class CollectionViewItemsController<CollectionType>: NSObject, UICollecti
   public func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
     cellFactory(self, collectionView, indexPath, collection[indexPath.section][indexPath.row])
   }
+
+  public func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
+      guard let configureSupplementaryView = configureSupplementaryView else {
+        fatalError("Property `configureSupplementaryView` must not be nil when using supplementary views")
+      }
+      return configureSupplementaryView(self, collectionView, kind, indexPath, collection[indexPath.section])
+  }
 
   // MARK: - Fallback data source object
   override public func forwardingTarget(for aSelector: Selector!) -> Any? {