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@taybenlor
Forked from toblerpwn/CustomCollectionFlowLayout.h
Last active January 1, 2016 08:59
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Adds support for sections with no header.
//
// CustomCollectionFlowLayout.h
// evilapples
//
// http://stackoverflow.com/questions/13511733/how-to-make-supplementary-view-float-in-uicollectionview-as-section-headers-do-i
//
//
#import <UIKit/UIKit.h>
@interface CustomCollectionFlowLayout : UICollectionViewFlowLayout
@end
//
// CustomCollectionFlowLayout.m
// evilapples
//
// http://stackoverflow.com/questions/13511733/how-to-make-supplementary-view-float-in-uicollectionview-as-section-headers-do-i
//
//
#import "CustomCollectionFlowLayout.h"
@implementation CustomCollectionFlowLayout
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
NSMutableArray *answer = [[super layoutAttributesForElementsInRect:rect] mutableCopy];
UICollectionView * const cv = self.collectionView;
CGPoint const contentOffset = cv.contentOffset;
NSMutableIndexSet *missingSections = [NSMutableIndexSet indexSet];
for (UICollectionViewLayoutAttributes *layoutAttributes in answer) {
if (layoutAttributes.representedElementCategory == UICollectionElementCategoryCell) {
[missingSections addIndex:layoutAttributes.indexPath.section];
}
}
for (UICollectionViewLayoutAttributes *layoutAttributes in answer) {
if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
[missingSections removeIndex:layoutAttributes.indexPath.section];
}
}
[missingSections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:idx];
UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
if (layoutAttributes) {
[answer addObject:layoutAttributes];
}
}];
for (UICollectionViewLayoutAttributes *layoutAttributes in answer) {
if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
NSInteger section = layoutAttributes.indexPath.section;
NSInteger numberOfItemsInSection = [cv numberOfItemsInSection:section];
NSIndexPath *firstObjectIndexPath = [NSIndexPath indexPathForItem:0 inSection:section];
NSIndexPath *lastObjectIndexPath = [NSIndexPath indexPathForItem:MAX(0, (numberOfItemsInSection - 1)) inSection:section];
BOOL cellsExist;
UICollectionViewLayoutAttributes *firstObjectAttrs;
UICollectionViewLayoutAttributes *lastObjectAttrs;
if (numberOfItemsInSection > 0) { // use cell data if items exist
cellsExist = YES;
firstObjectAttrs = [self layoutAttributesForItemAtIndexPath:firstObjectIndexPath];
lastObjectAttrs = [self layoutAttributesForItemAtIndexPath:lastObjectIndexPath];
} else { // else use the header and footer
cellsExist = NO;
firstObjectAttrs = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader
atIndexPath:firstObjectIndexPath];
lastObjectAttrs = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionFooter
atIndexPath:lastObjectIndexPath];
}
CGFloat topHeaderHeight = (cellsExist) ? CGRectGetHeight(layoutAttributes.frame) : 0;
CGFloat bottomHeaderHeight = CGRectGetHeight(layoutAttributes.frame);
CGRect frameWithEdgeInsets = UIEdgeInsetsInsetRect(layoutAttributes.frame,
cv.contentInset);
CGPoint origin = frameWithEdgeInsets.origin;
origin.y = MIN(
MAX(
contentOffset.y + cv.contentInset.top,
(CGRectGetMinY(firstObjectAttrs.frame) - topHeaderHeight)
),
(CGRectGetMaxY(lastObjectAttrs.frame) - bottomHeaderHeight)
);
layoutAttributes.zIndex = 1024;
layoutAttributes.frame = (CGRect){
.origin = origin,
.size = layoutAttributes.frame.size
};
}
}
return answer;
}
- (BOOL) shouldInvalidateLayoutForBoundsChange:(CGRect)newBound {
return YES;
}
@end
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