UICollectionViewCell水平缩放，中间大两边小效果的实现

//

//  CollectionViewFlowLayout.h

//  HorizontalScale

//

//  Created by zmx on 16/3/15.

//  Copyright © 2016年 zmx. All rights reserved.

//

#import <UIKit/UIKit.h>

@interface CollectionViewFlowLayout : UICollectionViewFlowLayout

@end

//

//  CollectionViewFlowLayout.m

//  HorizontalScale

//

//  Created by zmx on 16/3/15.

//  Copyright © 2016年 zmx. All rights reserved.

//

#import "CollectionViewFlowLayout.h"

@implementation CollectionViewFlowLayout

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

    NSArray *attrs = [selfdeepCopyWithArray:[superlayoutAttributesForElementsInRect:rect]];

    CGFloat contentOffsetX =self.collectionView.contentOffset.x;

    CGFloat collectionViewCenterX = self.collectionView.frame.size.width *0.5;

    for (UICollectionViewLayoutAttributes *attrin attrs) {

        CGFloat scale = 1 - fabs(attr.center.x - contentOffsetX - collectionViewCenterX) /self.collectionView.bounds.size.width;

        attr.transform = CGAffineTransformMakeScale(scale, scale);

    }

    return attrs;

}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {

    return YES;

}

//  每次都有图片居中

- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity {

    CGRect rect = CGRectMake(proposedContentOffset.x,0, self.collectionView.bounds.size.width,self.collectionView.bounds.size.height);

    NSArray *attrs = [superlayoutAttributesForElementsInRect:rect];

    CGFloat contentOffsetX =self.collectionView.contentOffset.x;

    CGFloat collectionViewCenterX = self.collectionView.frame.size.width *0.5;

    CGFloat minDistance = MAXFLOAT;

    for (UICollectionViewLayoutAttributes *attrin attrs) {

        CGFloat distance = attr.center.x - contentOffsetX - collectionViewCenterX;

        if (fabs(distance) <fabs(minDistance)) {

            minDistance = distance;

        }

    }

    proposedContentOffset.x += minDistance;

    return proposedContentOffset;

}

//  UICollectionViewFlowLayout has cached frame mismatch for index path这个警告来源主要是在使用layoutAttributesForElementsInRect：方法返回的数组时，没有使用该数组的拷贝对象，而是直接使用了该数组。解决办法对该数组进行拷贝，并且是深拷贝。

- (NSArray *)deepCopyWithArray:(NSArray *)arr {

    NSMutableArray *arrM = [NSMutableArrayarray];

    for (UICollectionViewLayoutAttributes *attrin arr) {

        [arrM addObject:[attr copy]];

    }

    return arrM;

}

@end

//

//  ViewController.m

//  HorizontalScale

//

//  Created by zmx on 16/3/15.

//  Copyright © 2016年 zmx. All rights reserved.

//

#import "ViewController.h"

#import "CollectionViewFlowLayout.h"

#import "Cell.h"

static NSString *identifier =@"c";

@interface ViewController () <UICollectionViewDataSource,UICollectionViewDelegate>

@property (weak, nonatomic) IBOutletUICollectionView *collectionView;

@property (weak, nonatomic) IBOutletCollectionViewFlowLayout *layout;

@end

@implementation ViewController

- (void)viewDidLoad {

    [superviewDidLoad];

    // Do any additional setup after loading the view, typically from a nib.

    [self.collectionViewregisterNib:[UINibnibWithNibName:@"Cell"bundle:nil]forCellWithReuseIdentifier:identifier];

}

- (void)viewDidLayoutSubviews {

    [superviewDidLayoutSubviews];

    self.layout.itemSize =CGSizeMake(100,100);

}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {

    return 20;

}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    Cell *cell = [collectionViewdequeueReusableCellWithReuseIdentifier:identifierforIndexPath:indexPath];

    return cell;

}

@end