关于UICollectionView横向分页滚动,cell左右排版功能的实现

#import <UIKit/UIKit.h>

@interface ELCVFlowLayout : UICollectionViewFlowLayout

@end

#import "ELCVFlowLayout.h"

@interface ELCVFlowLayout ()

@property (nonatomic, copy) NSMutableDictionary *sectionDic;
@property (strong, nonatomic) NSMutableArray *allAttributes;

@end

@implementation ELCVFlowLayout

- (instancetype)init
{
self = [super init];
if (self) {
self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
}
return self;
}

- (void)prepareLayout
{
[super prepareLayout];

_sectionDic = [NSMutableDictionary dictionary];
self.allAttributes = [NSMutableArray array];
//获取section的数量
NSUInteger section = [self.collectionView numberOfSections];

for (int sec = 0; sec < section; sec++) {
//获取每个section的cell个数
NSUInteger count = [self.collectionView numberOfItemsInSection:sec];

for (NSUInteger item = 0; item<count; item++) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:item inSection:sec];
//重新排列
UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];
[self.allAttributes addObject:attributes];

}
}

}

- (CGSize)collectionViewContentSize
{

//每个section的页码的总数
NSInteger actualLo = 0;
for (NSString *key in [_sectionDic allKeys]) {
actualLo += [_sectionDic[key] integerValue];
}

return CGSizeMake(actualLo*self.collectionView.frame.size.width, self.collectionView.contentSize.height);
}

- (void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)attributes
{

if(attributes.representedElementKind != nil)
{
return;
}

/*修改by lixinkai 2017.6.30
下面这两个方法 itemW、itemH
解决了同一个UICollectionView使用不同UICollectionViewCell的问题
*/
//attributes 的宽度
CGFloat itemW = attributes.frame.size.width;
//attributes 的高度
CGFloat itemH = attributes.frame.size.height;

//collectionView 的宽度
CGFloat width = self.collectionView.frame.size.width;
//collectionView 的高度
CGFloat height = self.collectionView.frame.size.height;
//每个attributes的下标值 从0开始
NSInteger itemIndex = attributes.indexPath.item;

CGFloat stride = (self.scrollDirection == UICollectionViewScrollDirectionHorizontal) ? width : height;

//获取现在的attributes是第几组
NSInteger section = attributes.indexPath.section;
//获取每个section的item的个数
NSInteger itemCount = [self.collectionView numberOfItemsInSection:section];

CGFloat offset = section * stride;

//计算x方向item个数
NSInteger xCount = (width / itemW);
//计算y方向item个数
NSInteger yCount = (height / itemH);
//计算一页总个数
NSInteger allCount = (xCount * yCount);
//获取每个section的页数，从0开始
NSInteger page = itemIndex / allCount;

//余数，用来计算item的x的偏移量
NSInteger remain = (itemIndex % xCount);

//取商，用来计算item的y的偏移量
NSInteger merchant = (itemIndex-page*allCount)/xCount;

//x方向每个item的偏移量
CGFloat xCellOffset = remain * itemW;
//y方向每个item的偏移量
CGFloat yCellOffset = merchant * itemH;

//获取每个section中item占了几页
NS
993b
Integer pageRe = (itemCount % allCount == 0)? (itemCount / allCount) : (itemCount / allCount) + 1;
//将每个section与pageRe对应，计算下面的位置
[_sectionDic setValue:@(pageRe) forKey:[NSString stringWithFormat:@"%ld", section]];

if(self.scrollDirection == UICollectionViewScrollDirectionHorizontal) {

NSInteger actualLo = 0;
//将每个section中的页数相加
for (NSString *key in [_sectionDic allKeys]) {
actualLo += [_sectionDic[key] integerValue];
}
//获取到的最后的数减去最后一组的页码数
actualLo -= [_sectionDic[[NSString stringWithFormat:@"%ld", [_sectionDic allKeys].count-1]] integerValue];
xCellOffset += page*width + actualLo*width;

} else {

yCellOffset += offset;
}

attributes.frame = CGRectMake(xCellOffset, yCellOffset, itemW, itemH);
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{

//    UICollectionViewLayoutAttributes *attr = [UICollectionViewLayoutAttributes  layoutAttributesForCellWithIndexPath:indexPath];
UICollectionViewLayoutAttributes *attr = [super layoutAttributesForItemAtIndexPath:indexPath].copy;

[self applyLayoutAttributes:attr];
return attr;
}

- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
return self.allAttributes;
}

@end