ios uicollectionview实现横向滚动

2、自定义UICollectionViewFlowLayout

LHHorizontalPageFlowlayout.h 实现

#import <UIKit/UIKit.h>
@interface LHHorizontalPageFlowlayout : UICollectionViewFlowLayout
/** 列间距 */
@property (nonatomic, assign) CGFloat columnSpacing;
/** 行间距 */
@property (nonatomic, assign) CGFloat rowSpacing;
/** collectionView的内边距 */
@property (nonatomic, assign) UIEdgeInsets edgeInsets;

/** 多少行 */
@property (nonatomic, assign) NSInteger rowCount;
/** 每行展示多少个item */
@property (nonatomic, assign) NSInteger itemCountPerRow;

//固定宽度
@property (nonatomic, assign) CGFloat itemWidth; //设置完这个，就会自动计算列间距
//固定高度
@property (nonatomic, assign) CGFloat itemHight;//设置完这个，就会自动计算行间距

/** 所有item的属性数组 */
@property (nonatomic, strong) NSMutableArray *attributesArrayM;

/** 设置行列间距及collectionView的内边距 */
- (void)setColumnSpacing:(CGFloat)columnSpacing rowSpacing:(CGFloat)rowSpacing edgeInsets:(UIEdgeInsets)edgeInsets;
/** 设置多少行及每行展示的item个数 */
- (void)setRowCount:(NSInteger)rowCount itemCountPerRow:(NSInteger)itemCountPerRow;

#pragma mark - 构造方法
/** 设置多少行及每行展示的item个数 */
+ (instancetype)horizontalPageFlowlayoutWithRowCount:(NSInteger)rowCount itemCountPerRow:(NSInteger)itemCountPerRow;
/** 设置多少行及每行展示的item个数 */
- (instancetype)initWithRowCount:(NSInteger)rowCount itemCountPerRow:(NSInteger)itemCountPerRow;

@end

LHHorizontalPageFlowlayout.m 实现

#import "LHHorizontalPageFlowlayout.h"

@implementation LHHorizontalPageFlowlayout

#pragma mark - Public
- (void)setColumnSpacing:(CGFloat)columnSpacing rowSpacing:(CGFloat)rowSpacing edgeInsets:(UIEdgeInsets)edgeInsets
{
 self.columnSpacing = columnSpacing;
 self.rowSpacing = rowSpacing;
 self.edgeInsets = edgeInsets;
}

- (void)setRowCount:(NSInteger)rowCount itemCountPerRow:(NSInteger)itemCountPerRow
{
 self.rowCount = rowCount;
 self.itemCountPerRow = itemCountPerRow;
}

#pragma mark - 构造方法
+ (instancetype)horizontalPageFlowlayoutWithRowCount:(NSInteger)rowCount itemCountPerRow:(NSInteger)itemCountPerRow
{
 return [[self alloc] initWithRowCount:rowCount itemCountPerRow:itemCountPerRow];
}

- (instancetype)initWithRowCount:(NSInteger)rowCount itemCountPerRow:(NSInteger)itemCountPerRow
{
 self = [super init];
 if (self) {
  self.rowCount = rowCount;
  self.itemCountPerRow = itemCountPerRow;
 }
 return self;
}


#pragma mark - 重写父类方法
- (instancetype)init
{
 self = [super init];
 if (self) {
  [self setColumnSpacing:0 rowSpacing:0 edgeInsets:UIEdgeInsetsZero];
 }
 return self;
}

/** 布局前做一些准备工作 */
- (void)prepareLayout
{
 [super prepareLayout];
 if (self.attributesArrayM && self.attributesArrayM.count > 0) {
  [self.attributesArrayM removeAllObjects];
 }
 
 // 从collectionView中获取到有多少个item
 NSInteger itemTotalCount = [self.collectionView numberOfItemsInSection:0];
 
 // 遍历出item的attributes,把它添加到管理它的属性数组中去
 for (int i = 0; i < itemTotalCount; i++) {
  NSIndexPath *indexpath = [NSIndexPath indexPathForItem:i inSection:0];
  UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexpath];
  [self.attributesArrayM addObject:attributes];
 }
}

/** 计算collectionView的滚动范围 */
- (CGSize)collectionViewContentSize
{
 // 计算出item的宽度
 CGFloat itemWidth = (self.collectionView.frame.size.width - self.edgeInsets.left - self.itemCountPerRow * self.columnSpacing) / self.itemCountPerRow;
 // 从collectionView中获取到有多少个item
 NSInteger itemTotalCount = [self.collectionView numberOfItemsInSection:0];
 
 // 理论上每页展示的item数目
 NSInteger itemCount = self.rowCount * self.itemCountPerRow;
 // 余数（用于确定最后一页展示的item个数）
 NSInteger remainder = itemTotalCount % itemCount;
 // 除数（用于判断页数）
 NSInteger pageNumber = itemTotalCount / itemCount;
 // 总个数小于self.rowCount * self.itemCountPerRow
 if (itemTotalCount <= itemCount) {
  pageNumber = 1;
 }else {
  if (remainder == 0) {
   pageNumber = pageNumber;
  }else {
   // 余数不为0,除数加1
   pageNumber = pageNumber + 1;
  }
 }
 
 CGFloat width = 0;
 // 考虑特殊情况(当item的总个数不是self.rowCount * self.itemCountPerRow的整数倍,并且余数小于每行展示的个数的时候)
 if (pageNumber > 1 && remainder != 0 && remainder < self.itemCountPerRow) {
  width = self.edgeInsets.left + (pageNumber - 1) * self.itemCountPerRow * (itemWidth + self.columnSpacing) + remainder * itemWidth + (remainder - 1)*self.columnSpacing + self.edgeInsets.right;
 }else {
  width = self.edgeInsets.left + pageNumber * self.itemCountPerRow * (itemWidth + self.columnSpacing) - self.columnSpacing + self.edgeInsets.right;
 }
 
 // 只支持水平方向上的滚动
 return CGSizeMake(width, 150);
}

/** 设置每个item的属性(主要是frame) */
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
 // item的宽高由行列间距和collectionView的内边距决定
 CGFloat itemWidth = (self.collectionView.frame.size.width) / self.itemCountPerRow;
 CGFloat itemHeight = (self.collectionView.frame.size.height) / self.rowCount;
 
 NSInteger item = indexPath.item;
 // 当前item所在的页
 NSInteger pageNumber = item / (self.rowCount * self.itemCountPerRow);
 NSInteger x = item % self.itemCountPerRow + pageNumber * self.itemCountPerRow;
 NSInteger y = item / self.itemCountPerRow - pageNumber * self.rowCount;
 
 // 计算出item的坐标
 CGFloat itemX = itemWidth * x;
 CGFloat itemY = itemHeight * y;
 
 UICollectionViewLayoutAttributes *attributes = [super layoutAttributesForItemAtIndexPath:indexPath];
 // 每个item的frame
 attributes.frame = CGRectMake(itemX, itemY, itemWidth, itemHeight);
 
 return attributes;
}

/** 返回collectionView视图中所有视图的属性数组 */
- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
 return self.attributesArrayM;
}


#pragma mark - Lazy
- (NSMutableArray *)attributesArrayM
{
 if (!_attributesArrayM) {
  _attributesArrayM = [NSMutableArray array];
 }
 return _attributesArrayM;
}
@end								 
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