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@evadne
Last active August 14, 2023 05:04
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Todd Laney’s enhancements to Sticky Headers + UICollectionViewFlowLayout
//
// StickyHeaderLayout.h
// Wombat
//
// Created by Todd Laney on 1/9/13.
// Copyright (c) 2013 ToddLa. All rights reserved.
//
// Modified from http://blog.radi.ws/post/32905838158/sticky-headers-for-uicollectionview-using THANKS!
//
#import <UIKit/UIKit.h>
@interface StickyHeaderLayout : UICollectionViewFlowLayout
@end
//
// StickyHeaderFlowLayout.m
// Wombat
//
// Created by Todd Laney on 1/9/13.
// Copyright (c) 2013 ToddLa. All rights reserved.
//
// Modified from http://blog.radi.ws/post/32905838158/sticky-headers-for-uicollectionview-using THANKS!
//
#import "StickyHeaderFlowLayout.h"
@implementation StickyHeaderFlowLayout
- (NSArray *) layoutAttributesForElementsInRect:(CGRect)rect {
NSMutableArray *answer = [[super layoutAttributesForElementsInRect:rect] mutableCopy];
NSMutableIndexSet *missingSections = [NSMutableIndexSet indexSet];
for (NSUInteger idx=0; idx<[answer count]; idx++) {
UICollectionViewLayoutAttributes *layoutAttributes = answer[idx];
if (layoutAttributes.representedElementCategory == UICollectionElementCategoryCell) {
[missingSections addIndex:layoutAttributes.indexPath.section]; // remember that we need to layout header for this section
}
if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
[answer removeObjectAtIndex:idx]; // remove layout of header done by our super, we will do it right later
idx--;
}
}
// layout all headers needed for the rect using self code
[missingSections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:idx];
UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
[answer addObject:layoutAttributes];
}];
return answer;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes *attributes = [super layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];
if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
UICollectionView * const cv = self.collectionView;
CGPoint const contentOffset = cv.contentOffset;
CGPoint nextHeaderOrigin = CGPointMake(INFINITY, INFINITY);
if (indexPath.section+1 < [cv numberOfSections]) {
UICollectionViewLayoutAttributes *nextHeaderAttributes = [super layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:[NSIndexPath indexPathForItem:0 inSection:indexPath.section+1]];
nextHeaderOrigin = nextHeaderAttributes.frame.origin;
}
CGRect frame = attributes.frame;
if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {
frame.origin.y = MIN(MAX(contentOffset.y, frame.origin.y), nextHeaderOrigin.y - CGRectGetHeight(frame));
}
else { // UICollectionViewScrollDirectionHorizontal
frame.origin.x = MIN(MAX(contentOffset.x, frame.origin.x), nextHeaderOrigin.x - CGRectGetWidth(frame));
}
attributes.zIndex = 1024;
attributes.frame = frame;
}
return attributes;
}
- (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];
return attributes;
}
- (UICollectionViewLayoutAttributes *)finalLayoutAttributesForDisappearingSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];
return attributes;
}
- (BOOL) shouldInvalidateLayoutForBoundsChange:(CGRect)newBound {
return YES;
}
@end
@pgpt10
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pgpt10 commented Dec 7, 2016

Can you please provide the code in Swift 3.0?

@poholo
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poholo commented Apr 9, 2018

Maybe can add the sectionInset of collectionView, like this:

`

    if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {
        frame.origin.x += self.sectionInset.left;
        frame.origin.y = MIN(MAX(contentOffset.y, frame.origin.y) + self.sectionInset.bottom, nextHeaderOrigin.y + self.sectionInset.bottom - CGRectGetHeight(frame));
    } else { // UICollectionViewScrollDirectionHorizontal
        frame.origin.x = MIN(MAX(contentOffset.x, frame.origin.x) + self.sectionInset.left, nextHeaderOrigin.x + self.sectionInset.left - CGRectGetWidth(frame));
        frame.origin.y += self.sectionInset.top;
    }
    frame.size = CGSizeMake(frame.size.width - self.sectionInset.left - self.sectionInset.bottom, frame.size.height - self.sectionInset.top - self.sectionInset.bottom);`

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