Merge pull request #109 from kishikawakatsumi/background-decoration-zindex

Promoted section items' zIndex to 1 if section has decoration items.

Author: kishikawakatsumi

Sources/IBPCollectionViewCompositionalLayout/IBPNSCollectionLayoutSection.m

@@ -38,4 +38,8 @@ - (BOOL)scrollsOrthogonally {
     return self.orthogonalScrollingBehavior != IBPUICollectionLayoutSectionOrthogonalScrollingBehaviorNone;
 }
 
+- (BOOL)hasBackgroundDecorationItem {
+    return self.decorationItems.count > 0;
+}
+
 @end

Sources/IBPCollectionViewCompositionalLayout/IBPNSCollectionLayoutSection_Private.h

@@ -7,6 +7,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 @property (nonatomic, copy) IBPNSCollectionLayoutGroup *group;
 @property (nonatomic, readonly) BOOL scrollsOrthogonally;
+@property (nonatomic, readonly) BOOL hasBackgroundDecorationItem;
 
 @end
 

Sources/IBPCollectionViewCompositionalLayout/IBPUICollectionViewCompositionalLayout.m

@@ -200,6 +200,7 @@ - (void)prepareLayout {
             }
 
             cellAttributes.frame = cellFrame;
+            cellAttributes.zIndex = layoutSection.hasBackgroundDecorationItem ? 1 : 0;
 
             if (!layoutSection.scrollsOrthogonally) {
                 cachedItemAttributes[indexPath] = cellAttributes;

Sources/IBPCollectionViewCompositionalLayout/include/IBPNSCollectionLayoutDecorationItem.h

@@ -36,7 +36,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (instancetype)init NS_UNAVAILABLE;
 + (instancetype)new NS_UNAVAILABLE;
 
-@property (nonatomic) NSInteger zIndex;
+@property (nonatomic) NSInteger zIndex; // default is 0; all other section items will be automatically be promoted to zIndex=1
 @property (nonatomic, readonly) NSString *elementKind;
 @property (nonatomic) IBPNSDirectionalEdgeInsets contentInsets;