collectionView 横向滑动 看图

// 扩展  （名称 ： UICollectionViewFlowLayout ）类

.h

#import <UIKit/UIKit.h>

@interface   名称  : UICollectionViewFlowLayout

@end

.m

#import "名称.h"

@interface 名称 ()

@property (nonatomic, copy) NSMutableDictionary *sectionDic;

@property (strong, nonatomic) NSMutableArray *allAttributes;

@end

@implementation 名称

- (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;

    }

    //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 / self.itemSize.width);

    //计算y方向item个数

    NSInteger yCount = (height / self.itemSize.height);

    //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 * self.itemSize.width;

    //y方向每个item的偏移量

    CGFloat yCellOffset = merchant * self.itemSize.height;

    //获取每个section中item占了几页

    NSInteger 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, self.itemSize.width, self.itemSize.height);

}

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

{

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

    [self applyLayoutAttributes:attr];

    return attr;

}

- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect

{

    return self.allAttributes;

}

@end

VC中 这样

    _dateArray = [@[@1, @2, @3, @4, @5, @6, @7, @8, @9, @10, @11, @12, @13] mutableCopy];

    //横向滚动

    ELCVFlowLayout *horizontalLayout = [[ELCVFlowLayout alloc] init];

//    UICollectionViewFlowLayout *horizontalLayout = [[UICollectionViewFlowLayout alloc] init];

    horizontalLayout.itemSize = CGSizeMake(kScreenWidth/4.0, kScreenWidth/2.0);

    _collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 100, self.view.frame.size.width, kScreenWidth) collectionViewLayout:horizontalLayout];

//    _collectionView.contentInset = UIEdgeInsetsMake(10, 10, 10, 10);

    _collectionView.pagingEnabled = YES;

    _collectionView.dataSource = self;

    _collectionView.delegate = self;

    _collectionView.showsVerticalScrollIndicator = NO;

    _collectionView.showsHorizontalScrollIndicator = NO;

    _collectionView.bounces = NO;

    _collectionView.pagingEnabled = YES;

    _collectionView.backgroundColor = [UIColor blueColor];

    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cell"];

    [self.view addSubview:_collectionView];