ViewController.m#

//
//  ViewController.m
//  CustomFlowLayout

//

#import "ViewController.h"
#import "TestCollectionViewCell.h"
#import "CustomFlowLayout.h"
@interface ViewController ()<UICollectionViewDataSource,UICollectionViewDelegate>

@end

@implementation ViewController

NSString *identifier = @"cell";

- (void)viewDidLoad {
    [super viewDidLoad];
    //創(chuàng)建布局對(duì)象
    CustomFlowLayout *flowLayout = [[CustomFlowLayout alloc] init];
    
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 20, 414, 200) collectionViewLayout:flowLayout];
    collectionView.delegate = self;
    collectionView.dataSource = self;
    [collectionView registerClass:[TestCollectionViewCell class] forCellWithReuseIdentifier:identifier];
    [self.view addSubview:collectionView];
    
    
    
}




- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return 20;
}


- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    TestCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
    
    cell.imgView.image = [UIImage imageNamed:@"10.png" ];
    return cell;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

TestCollectionViewCell.h#

//
//  TestCollectionViewCell.h
//  CustomFlowLayout
//

//

#import <UIKit/UIKit.h>

@interface TestCollectionViewCell : UICollectionViewCell

@property(nonatomic,strong)UIImageView *imgView;

@end

TestCollectionViewCell.m#

//
//  TestCollectionViewCell.m
//  UI_21_CustomFlowLayout
//

//

#import "TestCollectionViewCell.h"

@implementation TestCollectionViewCell

-(instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        
        self.imgView = [[UIImageView alloc] initWithFrame:self.contentView.bounds];
        
        [self.contentView addSubview:_imgView];
    }
    
    return self;
}


@end

CustomFlowLayout.m#

//
//  CustomFlowLayout.m
//  CustomFlowLayout
.
//

#import "CustomFlowLayout.h"

#define kItem  100

@implementation CustomFlowLayout


//做好一些準(zhǔn)備工作,初始化
//準(zhǔn)備布局
-(void)prepareLayout{
    
    //設(shè)置大小
    self.itemSize = CGSizeMake(kItem, kItem);
    //設(shè)置滾動(dòng)方向
    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    //最小行間距
    self.minimumLineSpacing = 50;
    
    
}

//是否時(shí)刻改變并且重新布局
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
    return YES;
}


//數(shù)組里放置的是每一個(gè)item設(shè)置的屬性(例如: frame等等)
-(NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{
    //從父類里獲取item放置屬性的數(shù)組
    NSArray *array = [super layoutAttributesForElementsInRect:rect];
    //獲取屏幕中心點(diǎn)的x坐標(biāo)
    CGFloat centerX = self.collectionView.frame.size.width/2 + self.collectionView.contentOffset.x;
    //遍歷
    for (UICollectionViewLayoutAttributes *attrs in array) {
        
        //item的中心點(diǎn)
        CGFloat itemCenterX = attrs.center.x;
        //縮放比例
        CGFloat scale = 1 + 0.5*(1 - ABS(itemCenterX - centerX))/200;
        //
        attrs.transform3D = CATransform3DMakeScale(scale, scale, 1);
    }

    return array;
}

@end