带有粘性标题的UICollectionView [英] UICollectionView with a sticky header
本文介绍了带有粘性标题的UICollectionView的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
@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]; //记住我们需要为此部分布局标题
}
if（[layoutAttributes.representedElementKind isEqualToString：UICollectionElementKindSectionHeader]）{
[answer removeObjectAtIndex：idx]; //删除我们的super完成的标题布局，我们将在以后做到
idx--;
}
}
//使用自身代码布局所需的所有头文件
[missingSections enumerateIndexesUsingBlock：^（NSUInteger idx，BOOL * stop）{
NSIndexPath * indexPath = [NSIndexPath indexPathForItem：0 inSection：idx];
UICollectionViewLayoutAttributes * layoutAttributes = [self layoutAttributesForSupplementaryViewOfKind：UICollectionElementKindSectionHeader atIndexPath：indexPath];
if（layoutAttributes！= nil）{
[answer addObject：layoutAttributes];
}
}];
返回答案;
}
- （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;
}
返回属性;
}
- （UICollectionViewLayoutAttributes *）initialLayoutAttributesForAppearingSupplementaryElementOfKind：（NSString *）kind atIndexPath：（NSIndexPath *）indexPath {
UICollectionViewLayoutAttributes * attributes = [self layoutAttributesForSupplementaryViewOfKind：kind atIndexPath：indexPath] ;
返回属性;
}
- （UICollectionViewLayoutAttributes *）finalLayoutAttributesForDisappearingSupplementaryElementOfKind：（NSString *）kind atIndexPath：（NSIndexPath *）indexPath {
UICollectionViewLayoutAttributes * attributes = [self layoutAttributesForSupplementaryViewOfKind：kind atIndexPath：indexPath];
返回属性;
}
- （BOOL）shouldInvalidateLayoutForBoundsChange：（CGRect）newBound {
返回YES;
}
@end
I found a blog on how to make sticky headers and it works great. Only thing is I don't think it takes into account the sectionInserts.
This is how its intended to look:
I have my inserts:
collectionViewFlowLayout.sectionInset = UIEdgeInsetsMake(16, 16, 16, 16);
With the sticky header, it is moved down by 16 pixles:
I tried tinking with the original code and I think the issue is with the last part:
layoutAttributes.frame = (CGRect){
.origin = CGPointMake(origin.x, origin.y),
.size = layoutAttributes.frame.size
If i change it to origin.y - 16, the header will start in the right location but when pushed up, 16 pixels of the head go off screen:
I'm not sure how to get it to take into account sectionInsects. Can anybody help?
Here is the code in full from the blog:
- (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];
[answer addObject:layoutAttributes];
}];
for (UICollectionViewLayoutAttributes *layoutAttributes in answer) {
if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
NSInteger section = layoutAttributes.indexPath.section;
NSInteger numberOfItemsInSection = [cv numberOfItemsInSection:section];
NSIndexPath *firstCellIndexPath = [NSIndexPath indexPathForItem:0 inSection:section];
NSIndexPath *lastCellIndexPath = [NSIndexPath indexPathForItem:MAX(0, (numberOfItemsInSection - 1)) inSection:section];
UICollectionViewLayoutAttributes *firstCellAttrs = [self layoutAttributesForItemAtIndexPath:firstCellIndexPath];
UICollectionViewLayoutAttributes *lastCellAttrs = [self layoutAttributesForItemAtIndexPath:lastCellIndexPath];
CGFloat headerHeight = CGRectGetHeight(layoutAttributes.frame);
CGPoint origin = layoutAttributes.frame.origin;
origin.y = MIN(
MAX(
contentOffset.y,
(CGRectGetMinY(firstCellAttrs.frame) - headerHeight)
),
(CGRectGetMaxY(lastCellAttrs.frame) - headerHeight)
);
layoutAttributes.zIndex = 1024;
layoutAttributes.frame = (CGRect){
.origin = origin,
.size = layoutAttributes.frame.size
};
}
}
return answer;
}
解决方案
Fix by Todd Laney to handle Horizontal and Vertical scrolling and to take into account the sectionInsets:
https://gist.github.com/evadne/4544569
@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];
if (layoutAttributes != nil) {
[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
这篇关于带有粘性标题的UICollectionView的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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