iOS使用UICollectionView实现横向滚动照片效果

// ViewController.m

// 下面使用到的宏和全局变量
#define ScreenW [UIScreen mainScreen].bounds.size.width
#define ScreenH [UIScreen mainScreen].bounds.size.height
static NSString *const cellID = @"cellID";

// 创建collectionView的代码
- (void)setupCollectionView
{
 // 使用系统自带的流布局（继承自UICollectionViewLayout）
 UICollectionViewFlowLayout *layout = ({
 UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
 // 每个cell的大小
 layout.itemSize   = CGSizeMake(180, 180);
 // 横向滚动
 layout.scrollDirection  = UICollectionViewScrollDirectionHorizontal;
 // cell间的间距
 layout.minimumLineSpacing  = 40;

 //第一个cell和最后一个cell居中显示（这里我的Demo里忘记改了我用的是160，最后微调数据cell的大小是180）
 CGFloat margin = (ScreenW - 180) * 0.5;
 layout.sectiOnInset= UIEdgeInsetsMake(0, margin, 0, margin);

 layout;
 });

 // 使用UICollectionView必须设置UICollectionViewLayout属性
 UICollectionView *collectiOnView= ({
 UICollectionView *collectiOnView= [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:layout];
 collectionView.center  = self.view.center;
 collectionView.bounds  = CGRectMake(0, 0, ScreenW, 200);
 collectionView.backgroundColor = [UIColor brownColor];
 // 这里千万记得在interface哪里写！！！
 collectionView.dataSource = self;
 [collectionView setShowsHorizontalScrollIndicator:NO];

 [self.view addSubview:collectionView];

 collectionView;
 });

 // 实现注册cell，其中PhotoCell是我自定义的cell，继承自UICollectionViewCell
 UINib *collectiOnNib= [UINib nibWithNibName:NSStringFromClass([PhotoCell class])
      bundle:nil];
 [collectionView registerNib:collectionNib
 forCellWithReuseIdentifier:cellID];
}

// UICollectionViewCellDataSource
- (NSInteger)collectionView:(UICollectionView *)collectionView
 numberOfItemsInSection:(NSInteger)section
{
 return 10;
}

- (__kindof UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
    cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
 PhotoCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellID 
    forIndexPath:indexPath];

 // 图片名是 0 ~ 9
 cell.imageName = [NSString stringWithFormat:@"%ld", (long)indexPath.row];

 return cell;
}

// 界面是一个xib文件，在cell里拖了个ImageView，约束上下左右都是10
// 图片名是数字 0 ~ 9

// PhotoCell.h
@property (nonatomic, strong) NSString *imageName;

// PhotoCell.m
@interface PhotoCell ()

@property (weak, nonatomic) IBOutlet UIImageView *imageView;

@end

@implementation PhotoCell

- (void)awakeFromNib {
 [super awakeFromNib];
 // Initialization code
}

- (void)setImageName:(NSString *)imageName
{
 _imageName = imageName;

 self.imageView.image = [UIImage imageNamed:imageName];
}

// MyFlowLayout.h
#import 

// 注意！继承自UICollectionViewFlowLayout，因为它继承自UICollectionViewLayout。
@interface TWLayout : UICollectionViewFlowLayout

// MyFlowLayout.m
/**
 * The default implementation of this method returns NO. Subclasses can override it and return an appropriate value based on whether changes in the bounds of the collection view require changes to the layout of cells and supplementary views.
 此方法的默认实现返回NO。 子类可以覆盖它，并根据 collection view 的 bounds 中的更改是否需要更改 cells 和 supplementary views(补充视图) 的布局返回适当的值。

 * If the bounds of the collection view change and this method returns YES, the collection view invalidates the layout by calling the invalidateLayoutWithContext: method.
 如果 collection view 的 bounds 更改并且此方法返回YES，则 collection view 通过调用invalidateLayoutWithContext：方法使布局更新。

 @param newBounds The new bounds of the collection view.
 @return YES if the collection view requires a layout update or NO if the layout does not need to change.
 */
- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
 return YES;
}


/**
 * Returns the layout attributes for all of the cells and views in the specified rectangle.
 返回指定矩形中所有cells和views的布局属性。

 @param rect * The rectangle (specified in the collection view's coordinate system) containing the target views.
  包含目标视图的矩形（在集合视图的坐标系中指定）。

 @return * An array of UICollectionViewLayoutAttributes objects representing the layout information for the cells and views. The default implementation returns nil.
  UICollectionViewLayoutAttributes对象数组，表示cell和view的布局信息。默认实现返回nil。
 */
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
 // 获取collectionView的宽带
 CGFloat collectiOnW= self.collectionView.bounds.size.width;

 // 获取布局属性数组
 NSArray *attrs = [super layoutAttributesForElementsInRect:self.collectionView.bounds];
 for (int i = 0; i