#import "CollectionFlowLayout.h"

@interface CollectionFlowLayout()

//存放每一个cell的属性

@property (nonatomic, retain) NSMutableArray *attributesArray;

@end

@implementation CollectionFlowLayout

/**

 重写系统prepareLayout方法 （设置item的坐标等属性）

 */

- (void)prepareLayout{

    [super prepareLayout];

    _attributesArray = [[NSMutableArray alloc] init];

    CGFloat inset  = self.collectionView.bounds.size.width * (/64.0f);

    inset = floor(inset);

    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;

    CGFloat totalWidth = self.collectionView.frame.size.width;

    self.collectionView.pagingEnabled = YES;

    NSUInteger  itemCount = [self.collectionView numberOfItemsInSection:];

    for (int i=; i<itemCount; i++) {

        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:];

        UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

        CGFloat baseOffsetForCurrentView =  i* self.collectionView.bounds.size.width;

        CGFloat currentOffset = self.collectionView.contentOffset.x;

        //通过偏移量currentOffset 和baseOffsetForCurrentView 差值 得到collectionView宽度的倍数

        //例如：当row为2时，是第三行，baseOffsetForCurrentView是： width*2 偏移量是 ：width*2

        //     滑动到第二行时 偏移量为：width，角度计算为 （width-width*2）/width 为-0.5

        //     滑动到第四行时 偏移量为：width*3，角度计算为 （width*3-width*2）/width 为0.5

        //     所以角度为 -0.5 —— 0.5变化，通过第二行和第四行的正负判断是左划还是右划确定axis值

        attributes.transform3D = [self transformfromAngle:(currentOffset-baseOffsetForCurrentView)/totalWidth/ xAxis:(currentOffset-baseOffsetForCurrentView)>?YES:NO];

        attributes.frame = CGRectMake(inset+(totalWidth)*i, , self.collectionView.bounds.size.width - ( *inset), self.collectionView.bounds.size.height * /);

        [_attributesArray addObject:attributes];

    }

}

/**

 当collection view的bounds改变时，布局需要告诉collection view是否需要重新计算布局

 */

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {

    return YES;

}

/**

 3D动画

 */

- (CATransform3D)transformfromAngle:(CGFloat )angle xAxis:(BOOL)axis

{

    CATransform3D t = CATransform3DIdentity;

    t.m34  = 1.0/-;

    t = CATransform3DRotate(t,angle, axis?:-,, );

    return t;

}

/**

 返回collectionView的界面显示大小

 */

- (CGSize)collectionViewContentSize{

    return  CGSizeMake(self.collectionView.frame.size.width*[self.collectionView numberOfItemsInSection:], self.collectionView.frame.size.height);

}

/**

 将所有的layoutAttributes重写布局

 */

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

    return _attributesArray;

}

@end