support section decoration

Author: Bluelich

BLCollectionViewTagLayout/Classes/BLCollectionViewTagLayout.h

@@ -16,6 +16,8 @@ typedef NS_ENUM (NSUInteger, BLCollectionViewTagLayoutItemRenderPolicy) {
     BLCollectionViewTagLayoutItemRenderCustom        = 3,//place item use custom algorithm
 };
 
+UIKIT_EXTERN NSString *const BLCollectionElementKindSectionDecoration;
+
 #pragma mark - UICollectionViewTagStyleLayout
 #pragma mark -
 IB_DESIGNABLE NS_CLASS_AVAILABLE_IOS(8_0)
@@ -24,58 +26,62 @@ IB_DESIGNABLE NS_CLASS_AVAILABLE_IOS(8_0)
  * The default size value is (50.0, 50.0).
  */
 @property (nonatomic) IBInspectable CGSize itemSize;
-/*
+/**
  * The default value of this property is 10.0.
  */
 @property (nonatomic) CGFloat minimumLineSpacing;
-/*
+/**
  * The default value of this property is 10.0.
  */
 @property (nonatomic) CGFloat minimumInteritemSpacing;
-/*
+/**
  * The default size values are (0, 0).
  */
 @property (nonatomic) CGSize headerReferenceSize;
-/*
+/**
  * The default size values are (0, 0).
  */
 @property (nonatomic) CGSize footerReferenceSize;
-/*
+/**
  * The default edge insets are all set to 0.
  *
- * It does not affect header footer，but for section items similar as UICollectionViewFlowLayout.
+ * It does not affect header footer，but for section items. Similar as UICollectionViewFlowLayout.
  */
 @property (nonatomic) UIEdgeInsets sectionInset;
-/*
-* The default value is CGFLOAT_MAX
-*
-* You can specify the value for section items height limitation.
-*
-* Note : This value is the height of the section elements,except the header footer and section inset.
-*/
+/**
+ * The default value is CGFLOAT_MAX
+ *
+ * You can specify the value for section items height limitation.
+ *
+ * Note : This value is the height of the section elements,except the header footer and section inset.
+ */
 @property (nonatomic) CGFloat  maximumSectionHeight;
-/*
+/**
  * The default is UICollectionViewScrollDirectionVertical.
  *
  * Note: UICollectionViewScrollDirectionHorizontal is unimplemented.
  */
 @property (nonatomic) UICollectionViewScrollDirection scrollDirection;
-/*
+/**
  * The default is BLCollectionViewTagLayoutItemRenderDefault.
  */
 @property (nonatomic) BLCollectionViewTagLayoutItemRenderPolicy itemRenderPolicy;
-/*
+/**
  * The default value of this property is NO.
  */
 @property (nonatomic) BOOL sectionHeadersPinToVisibleBounds;
-/*
+/**
  * The default value of this property is NO.
  */
 @property (nonatomic) BOOL sectionFootersPinToVisibleBounds;
+/**
+ * The default value of this property is NO.
+ */
+@property (nonatomic) BOOL sectionDecorationVisiable;
 @end
 
 @interface BLCollectionViewTagLayout (UICollectionViewContentInsetAdjustment)
-/*
+/**
  * Additional adjusted contentInset by system
  *
  * As usual, you don't need to care about this,the layout will fill in it automatically.
@@ -92,7 +98,7 @@ IB_DESIGNABLE NS_CLASS_AVAILABLE_IOS(8_0)
  */
 @property (nonatomic,assign) UIEdgeInsets  systemAdditionalAdjustedContentInset;
 
-/*
+/**
  * Automatically systemAdditionalAdjustedContentInset configuration
  * by frame and translucent of UINavigationBar and UITabBar (and status bar)
  *

BLCollectionViewTagLayout/Classes/BLCollectionViewTagLayout.m

@@ -7,28 +7,34 @@
 
 #import "BLCollectionViewTagLayout.h"
 
+NSString *const BLCollectionElementKindSectionDecoration = @"BLCollectionElementKindSectionDecoration";
+
 #pragma mark - UICollectionViewTagStyleLayoutSectionAttributes Declare
 #pragma mark -
 @interface UICollectionViewTagStyleLayoutSectionAttributes : NSObject<NSCopying>
 @property (nonatomic,strong) UICollectionViewLayoutAttributes            *header;
 @property (nonatomic,strong) NSArray<UICollectionViewLayoutAttributes *> *items;
 @property (nonatomic,strong) UICollectionViewLayoutAttributes            *footer;
+@property (nonatomic,strong) UICollectionViewLayoutAttributes            *decoration;
 + (instancetype)layoutAttributesWithHeader:(UICollectionViewLayoutAttributes *)header
                                      items:(NSArray<UICollectionViewLayoutAttributes *> *)items
-                                    footer:(UICollectionViewLayoutAttributes *)footer;
+                                    footer:(UICollectionViewLayoutAttributes *)footer
+                                decoration:(UICollectionViewLayoutAttributes *)decoration;
 @end
 #pragma mark - UICollectionViewTagStyleLayoutSectionAttributes Implementation
 #pragma mark -
 @implementation UICollectionViewTagStyleLayoutSectionAttributes
 + (instancetype)layoutAttributesWithHeader:(UICollectionViewLayoutAttributes *)header
                                      items:(NSArray<UICollectionViewLayoutAttributes *> *)items
                                     footer:(UICollectionViewLayoutAttributes *)footer
+                                decoration:(UICollectionViewLayoutAttributes *)decoration
 {
     UICollectionViewTagStyleLayoutSectionAttributes *obj =
     UICollectionViewTagStyleLayoutSectionAttributes.new;
     obj.header = header;
     obj.items  = items;
     obj.footer = footer;
+    obj.decoration = decoration;
     return obj;
 }
 - (id)copyWithZone:(NSZone *)zone
@@ -38,6 +44,7 @@ - (id)copyWithZone:(NSZone *)zone
     obj.header = self.header.copy;
     obj.items  = [[NSArray alloc] initWithArray:self.items copyItems:YES];
     obj.footer = self.footer.copy;
+    obj.decoration = self.decoration.copy;
     return obj;
 }
 @end
@@ -213,9 +220,22 @@ - (void)setup
     _itemRenderPolicy        = BLCollectionViewTagLayoutItemRenderDefault;
     _sectionHeadersPinToVisibleBounds = NO;
     _sectionFootersPinToVisibleBounds = NO;
+    _sectionDecorationVisiable        = NO;
     _invalidatedForPinSectionHeaderFootersToVisibleBounds = NO;
     _additionalAdjustedContentInset = UIEdgeInsetsZero;
 }
+- (void)registerNib:(UINib *)nib forDecorationViewOfKind:(NSString *)elementKind
+{
+    NSAssert([elementKind isEqualToString:BLCollectionElementKindSectionDecoration],@"Kind of %@ current unsupported",elementKind);
+    if (![elementKind isEqualToString:BLCollectionElementKindSectionDecoration]) return;
+    [super registerNib:nib forDecorationViewOfKind:elementKind];
+}
+- (void)registerClass:(Class)viewClass forDecorationViewOfKind:(NSString *)elementKind
+{
+    NSAssert([elementKind isEqualToString:BLCollectionElementKindSectionDecoration],@"Kind of %@ current unsupported",elementKind);
+    if (![elementKind isEqualToString:BLCollectionElementKindSectionDecoration]) return;
+    [super registerClass:viewClass forDecorationViewOfKind:elementKind];
+}
 - (void)invalidateLayoutWithContext:(UICollectionViewLayoutInvalidationContext *)context
 {
     [super invalidateLayoutWithContext:context];
@@ -285,6 +305,12 @@ - (void)setSectionFootersPinToVisibleBounds:(BOOL)sectionFootersPinToVisibleBoun
     _sectionFootersPinToVisibleBounds = sectionFootersPinToVisibleBounds;
     [self invalidateLayout];
 }
+- (void)setSectionDecorationVisiable:(BOOL)sectionDecorationVisiable
+{
+    if (_sectionDecorationVisiable == sectionDecorationVisiable) return;
+    _sectionDecorationVisiable = sectionDecorationVisiable;
+    [self invalidateLayout];
+}
 #pragma mark -
 - (id<BLCollectionViewDelegateTagStyleLayout>)delegate
 {
@@ -311,6 +337,11 @@ - (NSInteger)zIndexForHeaderFooter
         if (CGRectIntersectsRect(rect, obj.footer.frame) && obj.footer.frame.size.height > 0) {
             [layoutAttributes addObject:obj.footer];
         }
+        if (self.sectionDecorationVisiable) {
+            if (CGRectIntersectsRect(rect, obj.decoration.frame) && obj.decoration.frame.size.height > 0) {
+                [layoutAttributes addObject:obj.decoration];
+            }
+        }
     }
     return layoutAttributes.copy;
 }
@@ -409,7 +440,13 @@ - (void)setupLayoutAttributes
         attributesForFooter.frame = CGRectMake(0, maxY, maxContentWidth, footerReferenceSize.height);
         attributesForFooter.zIndex = self.zIndexForHeaderFooter;
 
-        [self.originSectionAttributes addObject:[UICollectionViewTagStyleLayoutSectionAttributes layoutAttributesWithHeader:attributesForHeader items:sortedAttributesForItems footer:attributesForFooter]];
+        //section decoration
+        UICollectionViewLayoutAttributes *attrubuteForDecoration = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:BLCollectionElementKindSectionDecoration withIndexPath:indexPathForHeaderFooter];
+        attrubuteForDecoration.frame = CGRectMake(-sectionInset.left, CGRectGetMinY(attributesForHeader.frame), maxContentWidth + sectionInset.left + sectionInset.right, CGRectGetMaxY(attributesForFooter.frame) - CGRectGetMinY(attributesForHeader.frame));
+        attrubuteForDecoration.zIndex = -self.zIndexForHeaderFooter;
+        
+        //
+        [self.originSectionAttributes addObject:[UICollectionViewTagStyleLayoutSectionAttributes layoutAttributesWithHeader:attributesForHeader items:sortedAttributesForItems footer:attributesForFooter decoration:attrubuteForDecoration]];
 
         maxY = CGRectGetMaxY(attributesForFooter.frame);
     }
@@ -436,12 +473,12 @@ - (void)updateAttributesForPinSectionHeaderFootersToVisibleBounds:(CGRect)newBou
     visibleRectForPinHeaderFooter.origin.y += topOffset;
     visibleRectForPinHeaderFooter.size.height -= topOffset;
     visibleRectForPinHeaderFooter.size.height -= bottomOffset;
-    // copy items
-    self.sectionAttributes = [[NSMutableArray alloc] initWithArray:self.originSectionAttributes copyItems:YES];
     if (self.collectionViewContentSize.height <= CGRectGetHeight(visibleRectForPinHeaderFooter)) {
         //does no need to pin header or footer to visible bounds any more.
         return;
     }
+    // copy items
+    self.sectionAttributes = [[NSMutableArray alloc] initWithArray:self.originSectionAttributes copyItems:YES];
     NSArray<UICollectionViewLayoutAttributes *> *attributes = [self layoutAttributesForElementsInRect:visibleRectForPinHeaderFooter sectionAttributes:self.originSectionAttributes];
     if (sectionHeadersShouldPinToVisibleBounds) {
         UICollectionViewLayoutAttributes *header =
@@ -539,7 +576,13 @@ - (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind
 }
 - (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString*)elementKind atIndexPath:(NSIndexPath *)indexPath
 {
-    return [super layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:indexPath];
+    if (indexPath.section >= self.sectionAttributes.count) return nil;
+    UICollectionViewTagStyleLayoutSectionAttributes *sectionAttributes = self.sectionAttributes[indexPath.section];
+    if (elementKind == BLCollectionElementKindSectionDecoration) {
+        return sectionAttributes.decoration;
+    }else{
+        return [super layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:indexPath];
+    }
 }
 #pragma mark -
 - (UICollectionViewLayoutInvalidationContext *)invalidationContextForBoundsChange:(CGRect)newBounds
@@ -615,6 +658,7 @@ @interface BLCollectionViewTagLayout (IBDESIGNABLE)
 @property (nonatomic) IBInspectable CGSize    footerSize;
 @property (nonatomic) IBInspectable BOOL      pinHeaders;
 @property (nonatomic) IBInspectable BOOL      pinFooters;
+@property (nonatomic) IBInspectable BOOL      useDecoration;
 @end
 
 @implementation BLCollectionViewTagLayout (IBDESIGNABLE)
@@ -714,6 +758,14 @@ - (BOOL)pinFooters
 {
     return self.sectionFootersPinToVisibleBounds;
 }
+- (void)setUseDecoration:(BOOL)useDecoration
+{
+    self.sectionDecorationVisiable = useDecoration;
+}
+- (BOOL)useDecoration
+{
+    return self.sectionDecorationVisiable;;
+}
 - (void)setRenderType:(NSInteger)renderType
 {
     self.itemRenderPolicy = renderType;

Example/BLCollectionViewTagLayout/BLViewController.m

@@ -75,6 +75,39 @@ - (void)swizzling_setContentSize:(CGSize)contentSize
 }
 @end
 
+@interface BLDecorationView : UICollectionReusableView
+@end
+@implementation BLDecorationView
+- (instancetype)initWithFrame:(CGRect)frame
+{
+    self = [super initWithFrame:frame];
+    if (self) {
+        self.backgroundColor = UIColor.blueColor;
+        self.layer.cornerRadius = 5;
+        self.clipsToBounds = YES;
+        UIButton *obj = UIButton.new;
+        [self addSubview:obj];
+        obj.translatesAutoresizingMaskIntoConstraints = NO;
+        [obj.centerXAnchor constraintEqualToAnchor:self.centerXAnchor].active = YES;
+        [obj.centerYAnchor constraintEqualToAnchor:self.centerYAnchor].active = YES;
+        [obj.widthAnchor constraintEqualToAnchor:self.widthAnchor].active = YES;
+        [obj.heightAnchor constraintEqualToAnchor:self.heightAnchor].active = YES;
+        [obj addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchUpInside];
+    }
+    return self;
+}
+- (void)buttonClicked:(UIButton *)sender
+{
+    sender.backgroundColor = [UIColor colorWithHue:0.5 saturation:0.5 brightness:arc4random()%256/255.f alpha:1];
+}
+- (void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes
+{
+    [super applyLayoutAttributes:layoutAttributes];
+    self.backgroundColor = layoutAttributes.indexPath.section % 2 ? UIColor.redColor : UIColor.blueColor;
+    self.layer.zPosition = -1;
+}
+@end
+
 @interface BLViewController ()<BLCollectionViewDelegateTagStyleLayout>
 @property (nonatomic,strong) NSArray<NSString *>  *alphabetArray;
 @property (nonatomic,strong) NSMutableArray<NSMutableArray *> *dataSource;
@@ -89,7 +122,7 @@ - (void)viewDidLoad {
 
     self.collectionView.contentInset = UIEdgeInsetsMake(44, 44, 44, 44);
 //    self.collectionView.scrollIndicatorInsets = UIEdgeInsetsMake(14, 0, 14, 0);
-    
+    [self.blCollectionViewLayout registerClass:BLDecorationView.class forDecorationViewOfKind:BLCollectionElementKindSectionDecoration];
     [self.blCollectionViewLayout
      autoConfigSystemAdditionalAdjustedContentInsetWith:UIApplication.sharedApplication.statusBarFrame
                                           navigationBar:self.navigationController.navigationBar
@@ -140,6 +173,7 @@ - (UINavigationBar *)navigationBar
         ];
         item.rightBarButtonItems =
         @[
+            [[UIBarButtonItem alloc] initWithTitle:@"Decoration" style:UIBarButtonItemStyleDone target:self action:@selector(showDecoration:)],
             [[UIBarButtonItem alloc] initWithTitle:@"UnPin" style:UIBarButtonItemStyleDone target:self action:@selector(unPin:)],
             [[UIBarButtonItem alloc] initWithTitle:@"Pin" style:UIBarButtonItemStyleDone target:self action:@selector(pin:)]
         ];
@@ -200,6 +234,16 @@ - (IBAction)unPin:(UIBarButtonItem *)sender
     self.blCollectionViewLayout.sectionHeadersPinToVisibleBounds = NO;
     self.blCollectionViewLayout.sectionFootersPinToVisibleBounds = NO;
 }
+- (IBAction)showDecoration:(UIBarButtonItem *)sender
+{
+    self.blCollectionViewLayout.sectionDecorationVisiable =
+    !self.blCollectionViewLayout.sectionDecorationVisiable;
+    if (self.blCollectionViewLayout.sectionDecorationVisiable) {
+        sender.title = @"Decoration";
+    }else{
+        sender.title = @"No Decoration";
+    }
+}
 - (IBAction)add:(UIBarButtonItem *)sender
 {
     if (arc4random() % 2) {
@@ -242,6 +286,9 @@ - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cell
 - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
 {
     UICollectionReusableView *view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:kind forIndexPath:indexPath];
+    if (kind == BLCollectionElementKindSectionDecoration) {
+        return view;
+    }
     UILabel *label = view.subviews.firstObject;
     if (!label) {
         label = UILabel.new;