Add support fox custom z index

yossiavramov · Jun 11, 2019 · d542a95 · d542a95
1 parent f1e8410
commit d542a95
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Showing 6 changed files with 58 additions and 10 deletions.
diff --git a/MagazineLayout/LayoutCore/ItemModel.swift b/MagazineLayout/LayoutCore/ItemModel.swift
@@ -21,11 +21,12 @@ struct ItemModel {
 
   // MARK: Lifecycle
 
-  init(sizeMode: MagazineLayoutItemSizeMode, height: CGFloat) {
+  init(sizeMode: MagazineLayoutItemSizeMode, height: CGFloat, zIndex: Int?) {
     id = NSUUID().uuidString
     self.sizeMode = sizeMode
     originInSection = .zero
     size = CGSize(width: 0, height: height)
+    self.zIndex = zIndex
   }
 
   // MARK: Internal
@@ -36,5 +37,6 @@ struct ItemModel {
   var originInSection: CGPoint
   var size: CGSize
   var preferredHeight: CGFloat?
-
+  var zIndex: Int?
+
 }
diff --git a/MagazineLayout/LayoutCore/ModelState.swift b/MagazineLayout/LayoutCore/ModelState.swift
@@ -547,9 +547,10 @@ final class ModelState {
     invalidateSectionMaxYsCacheForSectionIndices(startingAt: sectionIndex)
   }
 
-  func updateItemSizeMode(to sizeMode: MagazineLayoutItemSizeMode, forItemAt indexPath: IndexPath) {
+  func updateItemSizeMode(to sizeMode: MagazineLayoutItemSizeMode, zIndex: Int?, forItemAt indexPath: IndexPath) {
     currentSectionModels[indexPath.section].updateItemSizeMode(
       to: sizeMode,
+      zIndex: zIndex,
       atIndex: indexPath.item)
 
     invalidateSectionMaxYsCacheForSectionIndices(startingAt: indexPath.section)

diff --git a/MagazineLayout/LayoutCore/SectionModel.swift b/MagazineLayout/LayoutCore/SectionModel.swift
@@ -165,14 +165,15 @@ struct SectionModel {
     updateIndexOfFirstInvalidatedRowIfNecessary(toProposedIndex: 0)
   }
 
-  mutating func updateItemSizeMode(to sizeMode: MagazineLayoutItemSizeMode, atIndex index: Int) {
+  mutating func updateItemSizeMode(to sizeMode: MagazineLayoutItemSizeMode, zIndex: Int?, atIndex index: Int) {
     // Accessing this array using an unsafe, untyped (raw) pointer avoids expensive copy-on-writes
     // and Swift retain / release calls.
     let itemModelsPointer = UnsafeMutableRawPointer(mutating: &itemModels)
     let directlyMutableItemModels = itemModelsPointer.assumingMemoryBound(to: ItemModel.self)
 
     directlyMutableItemModels[index].sizeMode = sizeMode
-
+    directlyMutableItemModels[index].zIndex = zIndex
+
     if case let .static(staticHeight) = sizeMode.heightMode {
       directlyMutableItemModels[index].size.height = staticHeight
     }

diff --git a/MagazineLayout/Public/MagazineLayout.swift b/MagazineLayout/Public/MagazineLayout.swift
@@ -130,7 +130,7 @@ public final class MagazineLayout: UICollectionViewLayout {
         let numberOfItems = modelState.numberOfItems(inSectionAtIndex: sectionIndex, .afterUpdates)
         for itemIndex in 0..<numberOfItems {
           let indexPath = IndexPath(item: itemIndex, section: sectionIndex)
-          modelState.updateItemSizeMode(to: sizeModeForItem(at: indexPath), forItemAt: indexPath)
+          modelState.updateItemSizeMode(to: sizeModeForItem(at: indexPath), zIndex: zIndexForItem(at: indexPath), forItemAt: indexPath)
         }
       }
     }
@@ -163,7 +163,7 @@ public final class MagazineLayout: UICollectionViewLayout {
         }
 
         newHeaderLayoutAttributes[headerLocation]?.shouldVerticallySelfSize = heightMode == .dynamic
-        newHeaderLayoutAttributes[headerLocation]?.zIndex = numberOfItems + 1
+        newHeaderLayoutAttributes[headerLocation]?.zIndex = numberOfItems + Default.HeaderZIndexByAddingToNumberOfItems
       }
 
       // Create footer layout attributes if necessary
@@ -179,7 +179,7 @@ public final class MagazineLayout: UICollectionViewLayout {
         }
 
         newFooterLayoutAttributes[footerLocation]?.shouldVerticallySelfSize = heightMode == .dynamic
-        newFooterLayoutAttributes[footerLocation]?.zIndex = numberOfItems + 1
+        newFooterLayoutAttributes[footerLocation]?.zIndex = numberOfItems + Default.FooterZIndexByAddingToNumberOfItems
       }
 
       // Create background layout attributes if necessary
@@ -216,7 +216,12 @@ public final class MagazineLayout: UICollectionViewLayout {
           newItemLayoutAttributes[itemLocation]?.shouldVerticallySelfSize = true
         }
 
-        newItemLayoutAttributes[itemLocation]?.zIndex = numberOfItems - itemIndex
+
+        if let zIndex = zIndexForItem(at: itemLocation.indexPath) {
+          newItemLayoutAttributes[itemLocation]?.zIndex = zIndex
+        } else {
+          newItemLayoutAttributes[itemLocation]?.zIndex = numberOfItems - itemIndex
+        }
       }
     }
 
@@ -778,6 +783,17 @@ public final class MagazineLayout: UICollectionViewLayout {
       sizeModeForItemAt: indexPath)
   }
 
+  private func zIndexForItem(at indexPath: IndexPath) -> Int? {
+    guard let delegateMagazineLayout = delegateMagazineLayout else {
+      return nil
+    }
+
+    return delegateMagazineLayout.collectionView(
+      currentCollectionView,
+      layout: self,
+      zIndexForItemAt: indexPath)
+  }
+
   private func initialItemHeight(from itemSizeMode: MagazineLayoutItemSizeMode) -> CGFloat {
     switch itemSizeMode.heightMode {
     case let .static(staticHeight):
@@ -868,9 +884,11 @@ public final class MagazineLayout: UICollectionViewLayout {
 
   private func itemModelForItem(at indexPath: IndexPath) -> ItemModel {
     let itemSizeMode = sizeModeForItem(at: indexPath)
+    let zIndex = zIndexForItem(at: indexPath)
     return ItemModel(
       sizeMode: itemSizeMode,
-      height: initialItemHeight(from: itemSizeMode))
+      height: initialItemHeight(from: itemSizeMode),
+      zIndex: zIndex)
   }
 
   private func headerModelForHeader(

diff --git a/MagazineLayout/Public/Types/MagazineLayout+Default.swift b/MagazineLayout/Public/Types/MagazineLayout+Default.swift
@@ -35,6 +35,8 @@ extension MagazineLayout {
     public static let SectionInsets: UIEdgeInsets = .zero
     public static let ItemInsets: UIEdgeInsets = .zero
 
+    public static let HeaderZIndexByAddingToNumberOfItems: Int = 1
+    public static let FooterZIndexByAddingToNumberOfItems: Int = 1
   }
 
 }
diff --git a/MagazineLayout/Public/UICollectionViewDelegateMagazineLayout.swift b/MagazineLayout/Public/UICollectionViewDelegateMagazineLayout.swift
@@ -31,6 +31,20 @@ public protocol UICollectionViewDelegateMagazineLayout: UICollectionViewDelegate
     sizeModeForItemAt indexPath: IndexPath)
     -> MagazineLayoutItemSizeMode
 
+  ///   Asks the delegate for the zIndex of the specified item.
+  ///
+  ///   - Parameters:
+  ///      - collectionView: The collection view using the layout.
+  ///      - collectionViewLayout: The layout requesting the information.
+  ///      - indexPath: The index path of the item.
+  ///
+  ///   - Returns: The zIndex of the specified item. Returns 0 for default zIndex
+  func collectionView(
+    _ collectionView: UICollectionView,
+    layout collectionViewLayout: UICollectionViewLayout,
+    zIndexForItemAt indexPath: IndexPath)
+    -> Int?
+
   ///   Asks the delegate for the visibility mode of the header in the specified section.
   ///
   ///   - Parameters:
@@ -136,3 +150,13 @@ public protocol UICollectionViewDelegateMagazineLayout: UICollectionViewDelegate
     -> UIEdgeInsets
 
 }
+
+public extension UICollectionViewDelegateMagazineLayout {
+  func collectionView(
+    _ collectionView: UICollectionView,
+    layout collectionViewLayout: UICollectionViewLayout,
+    zIndexForItemAt indexPath: IndexPath)
+    -> Int? {
+      return nil
+  }
+}