An advanced example about the UICollectionView and custom layout NEED QuartzCore.framework

LineLayout.h

/*
     File: LineLayout.h
 Abstract: Simple flow layout to lay out items in a line.
 
  Version: 1.0
 
 Disclaimer: IMPORTANT:  This Apple software is supplied to you by Apple
 Inc. ("Apple") in consideration of your agreement to the following
 terms, and your use, installation, modification or redistribution of
 this Apple software constitutes acceptance of these terms.  If you do
 not agree with these terms, please do not use, install, modify or
 redistribute this Apple software.
 
 In consideration of your agreement to abide by the following terms, and
 subject to these terms, Apple grants you a personal, non-exclusive
 license, under Apple's copyrights in this original Apple software (the
 "Apple Software"), to use, reproduce, modify and redistribute the Apple
 Software, with or without modifications, in source and/or binary forms;
 provided that if you redistribute the Apple Software in its entirety and
 without modifications, you must retain this notice and the following
 text and disclaimers in all such redistributions of the Apple Software.
 Neither the name, trademarks, service marks or logos of Apple Inc. may
 be used to endorse or promote products derived from the Apple Software
 without specific prior written permission from Apple.  Except as
 expressly stated in this notice, no other rights or licenses, express or
 implied, are granted by Apple herein, including but not limited to any
 patent rights that may be infringed by your derivative works or by other
 works in which the Apple Software may be incorporated.
 
 The Apple Software is provided by Apple on an "AS IS" basis.  APPLE
 MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION
 THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS
 FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND
 OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.
 
 IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL
 OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,
 MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED
 AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),
 STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.
 
 Copyright (C) 2012 Apple Inc. All Rights Reserved.
 
 
 WWDC 2012 License
 
 NOTE: This Apple Software was supplied by Apple as part of a WWDC 2012
 Session. Please refer to the applicable WWDC 2012 Session for further
 information.
 
 IMPORTANT: This Apple software is supplied to you by Apple
 Inc. ("Apple") in consideration of your agreement to the following
 terms, and your use, installation, modification or redistribution of
 this Apple software constitutes acceptance of these terms.  If you do
 not agree with these terms, please do not use, install, modify or
 redistribute this Apple software.
 
 In consideration of your agreement to abide by the following terms, and
 subject to these terms, Apple grants you a non-exclusive license, under
 Apple's copyrights in this original Apple software (the "Apple
 Software"), to use, reproduce, modify and redistribute the Apple
 Software, with or without modifications, in source and/or binary forms;
 provided that if you redistribute the Apple Software in its entirety and
 without modifications, you must retain this notice and the following
 text and disclaimers in all such redistributions of the Apple Software.
 Neither the name, trademarks, service marks or logos of Apple Inc. may
 be used to endorse or promote products derived from the Apple Software
 without specific prior written permission from Apple.  Except as
 expressly stated in this notice, no other rights or licenses, express or
 implied, are granted by Apple herein, including but not limited to any
 patent rights that may be infringed by your derivative works or by other
 works in which the Apple Software may be incorporated.
 
 The Apple Software is provided by Apple on an "AS IS" basis.  APPLE
 MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION
 THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS
 FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND
 OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.
 
 IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL
 OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,
 MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED
 AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),
 STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.
 
 */

#import <UIKit/UIKit.h>

@interface LineLayout : UICollectionViewFlowLayout

@end

LineLayout.m

/*
     File: LineLayout.m
 Abstract: Simple flow layout to lay out items in a line.
 
  Version: 1.0
 
 Disclaimer: IMPORTANT:  This Apple software is supplied to you by Apple
 Inc. ("Apple") in consideration of your agreement to the following
 terms, and your use, installation, modification or redistribution of
 this Apple software constitutes acceptance of these terms.  If you do
 not agree with these terms, please do not use, install, modify or
 redistribute this Apple software.
 
 In consideration of your agreement to abide by the following terms, and
 subject to these terms, Apple grants you a personal, non-exclusive
 license, under Apple's copyrights in this original Apple software (the
 "Apple Software"), to use, reproduce, modify and redistribute the Apple
 Software, with or without modifications, in source and/or binary forms;
 provided that if you redistribute the Apple Software in its entirety and
 without modifications, you must retain this notice and the following
 text and disclaimers in all such redistributions of the Apple Software.
 Neither the name, trademarks, service marks or logos of Apple Inc. may
 be used to endorse or promote products derived from the Apple Software
 without specific prior written permission from Apple.  Except as
 expressly stated in this notice, no other rights or licenses, express or
 implied, are granted by Apple herein, including but not limited to any
 patent rights that may be infringed by your derivative works or by other
 works in which the Apple Software may be incorporated.
 
 The Apple Software is provided by Apple on an "AS IS" basis.  APPLE
 MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION
 THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS
 FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND
 OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.
 
 IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL
 OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,
 MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED
 AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),
 STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.
 
 Copyright (C) 2012 Apple Inc. All Rights Reserved.
 
 
 WWDC 2012 License
 
 NOTE: This Apple Software was supplied by Apple as part of a WWDC 2012
 Session. Please refer to the applicable WWDC 2012 Session for further
 information.
 
 IMPORTANT: This Apple software is supplied to you by Apple
 Inc. ("Apple") in consideration of your agreement to the following
 terms, and your use, installation, modification or redistribution of
 this Apple software constitutes acceptance of these terms.  If you do
 not agree with these terms, please do not use, install, modify or
 redistribute this Apple software.
 
 In consideration of your agreement to abide by the following terms, and
 subject to these terms, Apple grants you a non-exclusive license, under
 Apple's copyrights in this original Apple software (the "Apple
 Software"), to use, reproduce, modify and redistribute the Apple
 Software, with or without modifications, in source and/or binary forms;
 provided that if you redistribute the Apple Software in its entirety and
 without modifications, you must retain this notice and the following
 text and disclaimers in all such redistributions of the Apple Software.
 Neither the name, trademarks, service marks or logos of Apple Inc. may
 be used to endorse or promote products derived from the Apple Software
 without specific prior written permission from Apple.  Except as
 expressly stated in this notice, no other rights or licenses, express or
 implied, are granted by Apple herein, including but not limited to any
 patent rights that may be infringed by your derivative works or by other
 works in which the Apple Software may be incorporated.
 
 The Apple Software is provided by Apple on an "AS IS" basis.  APPLE
 MAKES NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION
 THE IMPLIED WARRANTIES OF NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS
 FOR A PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND
 OPERATION ALONE OR IN COMBINATION WITH YOUR PRODUCTS.
 
 IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL
 OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 INTERRUPTION) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION,
 MODIFICATION AND/OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED
 AND WHETHER UNDER THEORY OF CONTRACT, TORT (INCLUDING NEGLIGENCE),
 STRICT LIABILITY OR OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.
 
 */

#import "LineLayout.h"


#define ITEM_SIZE 200.0

@implementation LineLayout

#define ACTIVE_DISTANCE 200
#define ZOOM_FACTOR 0.3

-(id)init
{
    self = [super init];
    if (self) {
        self.itemSize = CGSizeMake(ITEM_SIZE, ITEM_SIZE);
        self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
        self.sectionInset = UIEdgeInsetsMake(50, 0.0, 50, 0.0);
        self.minimumInteritemSpacing = 500.0;
        self.minimumLineSpacing = 50.0;
    }
    return self;
}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)oldBounds
{
    return YES;
}

-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray* array = [super layoutAttributesForElementsInRect:rect];
    CGRect visibleRect;
    visibleRect.origin = self.collectionView.contentOffset;
    visibleRect.size = self.collectionView.bounds.size;
    
    for (UICollectionViewLayoutAttributes* attributes in array) {
        if (CGRectIntersectsRect(attributes.frame, rect)) {
            CGFloat distance = CGRectGetMidX(visibleRect) - attributes.center.x;
            CGFloat normalizedDistance = distance / ACTIVE_DISTANCE;
            if (ABS(distance) < ACTIVE_DISTANCE) {
                CGFloat zoom = 1 + ZOOM_FACTOR*(1 - ABS(normalizedDistance));
                attributes.transform3D = CATransform3DMakeScale(zoom, zoom, 1.0);
                attributes.zIndex = 1;
            }
        }
    }
    return array;
}


- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
{
    CGFloat offsetAdjustment = MAXFLOAT;
    CGFloat horizontalCenter = proposedContentOffset.x + (CGRectGetWidth(self.collectionView.bounds) / 2.0);
    
    CGRect targetRect = CGRectMake(proposedContentOffset.x, 0.0, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
    NSArray* array = [super layoutAttributesForElementsInRect:targetRect];
    
    for (UICollectionViewLayoutAttributes* layoutAttributes in array) {
        CGFloat itemHorizontalCenter = layoutAttributes.center.x;
        if (ABS(itemHorizontalCenter - horizontalCenter) < ABS(offsetAdjustment)) {
            offsetAdjustment = itemHorizontalCenter - horizontalCenter;
        }
    }    
    return CGPointMake(proposedContentOffset.x + offsetAdjustment, proposedContentOffset.y);
}

@end

main.m

//
//  main.m
//  AdvancedUICollectionViewLayout
//
//  Created by Puttin Wong on 4/8/13.
//  Copyright (c) 2013 Puttin Wong. All rights reserved.
//

#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>

#import "LineLayout.h"
#pragma mark -
#pragma mark DemoCollectionViewCell
@interface DemoCollectionViewCell : UICollectionViewCell

-(void)setImage:(UIImage *)image;

@property (strong, nonatomic) UILabel* label;
@property (nonatomic, strong) UIImageView *imageView;

@end

@implementation DemoCollectionViewCell
- (id)initWithFrame:(CGRect)frame
{
    if (!(self = [super initWithFrame:frame])) return nil;
    
    self.imageView = [[UIImageView alloc] initWithFrame:CGRectInset(CGRectMake(0, 0, CGRectGetWidth(frame), CGRectGetHeight(frame)), 2, 2)];
    self.imageView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    [self.contentView addSubview:self.imageView];
    self.label = [[UILabel alloc] initWithFrame:CGRectInset(CGRectMake(0, 0, CGRectGetWidth(frame), CGRectGetHeight(frame)), 5, 5)];
    self.label.autoresizingMask = UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth;
    self.label.textAlignment = NSTextAlignmentCenter;
    self.label.font = [UIFont boldSystemFontOfSize:40.0];
    self.label.backgroundColor = [UIColor clearColor];
    self.label.textColor = [UIColor blackColor];
    [self.contentView addSubview:self.label];;
    // make sure we rasterize nicely for retina
    self.layer.rasterizationScale = [UIScreen mainScreen].scale;
    self.layer.shouldRasterize = YES;
    
    self.backgroundColor = [UIColor whiteColor];
    
    return self;
}

-(void)prepareForReuse
{
    [self setImage:nil];
}

-(void)setImage:(UIImage *)image
{
    self.imageView.image = image;
}

-(void)setText:(NSString *)str
{
    self.label.text = str;
}

@end

#pragma mark -
#pragma mark StackedPhotoLayout

static NSUInteger const RotationCount = 32;
static NSUInteger const RotationStride = 3;
static NSUInteger const PhotoCellBaseZIndex = 100;
static NSString * const PhotoCellKind = @"PhotoCell";
static float imageItemSize = 90.0f;
@interface StackedPhotoLayout : UICollectionViewLayout

@property (nonatomic) UIEdgeInsets sectionInset;
@property (nonatomic) CGSize itemSize;
@property (nonatomic) CGFloat minimumInterItemSpacing;
@property (nonatomic) CGFloat minimumLineSpacing;

@property (nonatomic, strong) NSDictionary *layoutInfo;
@property (nonatomic, strong) NSArray *rotations;

@end

@implementation StackedPhotoLayout{
    NSUInteger maxColumnNum;
    CGFloat realInterItemSpacing;
}

- (id)init
{
    self = [super init];
    if (self) {
        [self setup];
    }
    
    return self;
}
- (void)setup
{
    self.itemSize = CGSizeMake(imageItemSize, imageItemSize);
    self.sectionInset = UIEdgeInsetsMake(10, 10, 10, 10);
    self.minimumInterItemSpacing = 15;
    self.minimumLineSpacing = 15;
    
    
    // create rotations at load so that they are consistent during prepareLayout
    NSMutableArray *rotations = [NSMutableArray arrayWithCapacity:RotationCount];
    CGFloat percentage = 0.0f;
    for (NSInteger i = 0; i < RotationCount; i++) {
        // ensure that each angle is different enough to be seen
        CGFloat newPercentage = 0.0f;
        do {
            newPercentage = ((CGFloat)(arc4random() % 220) - 110) * 0.0001f;
        } while (fabsf(percentage - newPercentage) < 0.006);
        percentage = newPercentage;
        
        CGFloat angle = 2 * M_PI * (1.0f + percentage);
        CATransform3D transform = CATransform3DMakeRotation(angle, 0.0f, 0.0f, 1.0f);
        
        [rotations addObject:[NSValue valueWithCATransform3D:transform]];
    }
    self.rotations = rotations;
     
    
}

- (void)prepareLayout
{
    maxColumnNum = [self maxColumn];
    realInterItemSpacing = [self realInterItemSpacing];
    //    NSLog(@"%u %f",maxColumnNum,realInterItemSpacing);
    
    NSMutableDictionary *newLayoutInfo = [NSMutableDictionary dictionary];
    NSMutableDictionary *cellLayoutInfo = [NSMutableDictionary dictionary];
    
    NSInteger sectionCount = [self.collectionView numberOfSections];
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];
    
    for (NSInteger section = 0; section < sectionCount; section++) {
        NSInteger itemCount = [self.collectionView numberOfItemsInSection:section];
        
        for (NSInteger item = 0; item < itemCount; item++) {
            indexPath = [NSIndexPath indexPathForItem:item inSection:section];
            
            UICollectionViewLayoutAttributes *itemAttributes =
            [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
            itemAttributes.frame = [self frameForAlbumPhotoAtIndexPath:indexPath];
            itemAttributes.transform3D = [self transformForAlbumPhotoAtIndex:indexPath];
            itemAttributes.zIndex = PhotoCellBaseZIndex + itemCount - item;
            
            cellLayoutInfo[indexPath] = itemAttributes;
        }
    }
    
    newLayoutInfo[PhotoCellKind] = cellLayoutInfo;
    
    self.layoutInfo = newLayoutInfo;
}
-(CGSize)collectionViewContentSize
{
    NSUInteger rowCount = [self.collectionView numberOfSections]/maxColumnNum;
    if ([self.collectionView numberOfSections] % maxColumnNum) rowCount++;
    CGFloat height = self.sectionInset.top + rowCount * self.itemSize.height + (rowCount - 1) * self.minimumLineSpacing + self.sectionInset.bottom;
    
    return CGSizeMake([self collectionView].frame.size.width, height);
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return self.layoutInfo[PhotoCellKind][indexPath];
}

-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSMutableArray *allAttributes = [NSMutableArray arrayWithCapacity:self.layoutInfo.count];
    
    [self.layoutInfo enumerateKeysAndObjectsUsingBlock:^(NSString *elementIdentifier, NSDictionary *elementsInfo, BOOL *stop) {
        [elementsInfo enumerateKeysAndObjectsUsingBlock:^(NSIndexPath *indexPath, UICollectionViewLayoutAttributes *attributes, BOOL *innerStop) {
            if (CGRectIntersectsRect(rect, attributes.frame)) {
                [allAttributes addObject:attributes];
            }
        }];
    }];
    
    return allAttributes;
}

- (NSUInteger)maxColumn {
    NSUInteger i = 0;
    BOOL done = NO;
    while (done == NO) {
        NSInteger leftSpace = [self collectionView].frame.size.width - self.sectionInset.left - self.sectionInset.right - i * self.itemSize.width - i * self.minimumInterItemSpacing ;
        if (leftSpace < self.itemSize.width) {
            done = YES;
        } else {
            i++;
        }
    }
    if (i==0) {
        NSLog(@"ERROR: CANNOT put even one item in a row");
    }
    return i;
}

- (CGFloat)realInterItemSpacing {
    if (maxColumnNum == 1) {
        return self.minimumInterItemSpacing;
    }
    return ([self collectionView].frame.size.width - self.sectionInset.left - self.sectionInset.right - maxColumnNum * self.itemSize.width) / (maxColumnNum - 1);
}

- (NSIndexPath *)rowAndColumnForSection:(NSUInteger)section {
    NSUInteger row = section/maxColumnNum;
    NSUInteger column = section % maxColumnNum;
    
    return [NSIndexPath indexPathForRow:column inSection:row];
}

- (CGRect)frameForAlbumPhotoAtIndexPath:(NSIndexPath *)indexPath
{
    NSUInteger section = indexPath.section;
    NSIndexPath *rc = [self rowAndColumnForSection:section];
    
    CGFloat originX = self.sectionInset.left + (self.itemSize.width + realInterItemSpacing)* rc.row;
    CGFloat originY = self.sectionInset.top + (self.itemSize.height + self.minimumLineSpacing)* rc.section;
    
    return CGRectMake(originX, originY, self.itemSize.width, self.itemSize.width);
}

- (CATransform3D)transformForAlbumPhotoAtIndex:(NSIndexPath *)indexPath
{
    NSInteger offset = (indexPath.section * RotationStride + indexPath.item);
    return [self.rotations[offset % RotationCount] CATransform3DValue];
}
@end

#pragma mark -
#pragma mark DemoCollectionViewController

static NSString *ItemIdentifier = @"ItemIdentifier";
static float imageSize = 90.0f;

@interface DemoCollectionViewController : UICollectionViewController

@property (nonatomic, strong) NSMutableArray *albums;
@property (nonatomic, strong) NSMutableArray *realAlbums;

@end

@implementation DemoCollectionViewController


-(void)loadView
{
    StackedPhotoLayout *stackedLayout = [[StackedPhotoLayout alloc] init];
    self.collectionView = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:stackedLayout];
    [self.collectionView registerClass:[DemoCollectionViewCell class] forCellWithReuseIdentifier:ItemIdentifier];
    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;
    
    self.collectionView.indicatorStyle = UIScrollViewIndicatorStyleWhite;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh target:self action:@selector(reset)];
    
    self.albums = [NSMutableArray array];
    
    NSUInteger randMax = 10;
    NSUInteger loopCount = (NSUInteger)(arc4random()%randMax+15);
    for (NSUInteger i =0; i<loopCount; i++) {
        NSMutableArray *arr=[[NSMutableArray alloc] init];
        NSUInteger loopCount1 = (NSUInteger)(arc4random()%randMax+5);
        for (NSUInteger j =0; j<loopCount1; j++) {
            [arr addObject:[DemoCollectionViewController imageWithRandomColorInSize:CGSizeMake(imageSize, imageSize)]];
        }
        [self.albums addObject:arr];
    }
    self.realAlbums = [self.albums mutableCopy];
}

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
    [super willRotateToInterfaceOrientation:toInterfaceOrientation duration:duration];
//    [self.collectionView reloadData];
    [self.collectionView.collectionViewLayout invalidateLayout];
}

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

#pragma mark - Get A Image
+(UIColor *)randomColor
{
    static BOOL seeded = NO;
    if (!seeded) {seeded = YES; srandom(time(NULL));}
    CGFloat red =  (CGFloat)random()/(CGFloat)RAND_MAX;
    CGFloat blue = (CGFloat)random()/(CGFloat)RAND_MAX;
    CGFloat green = (CGFloat)random()/(CGFloat)RAND_MAX;
    return [UIColor colorWithRed:red green:green blue:blue alpha:1.0f];
}

+ (UIImage *)imageWithRandomColorInSize:(CGSize)size {
    return [self imageWithColor:[self randomColor] andSize:size];
}

+ (UIImage *)imageWithColor:(UIColor *)color andSize:(CGSize)size {
    CGRect rect = CGRectMake(0.0f, 0.0f, size.height, size.width);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return image;
}

#pragma mark - UICollectionView DataSource & Delegate methods

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return self.realAlbums.count;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return [self.realAlbums[section] count];
}

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    DemoCollectionViewCell *cell = (DemoCollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:ItemIdentifier forIndexPath:indexPath];
    [cell setImage:[self.realAlbums[indexPath.section] objectAtIndex:indexPath.row]];
    [cell setText:[NSString stringWithFormat:@"%u,%u",indexPath.section,indexPath.row]];
    
    return cell;
}

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSMutableIndexSet *set = [[NSMutableIndexSet alloc] init];
    for (NSUInteger i =0; i<[self numberOfSectionsInCollectionView:collectionView]; i++) {
        if (i != indexPath.section) {
            [set addIndex:i];
        }
    }
    [self.realAlbums removeObjectsAtIndexes:set];
    [collectionView deleteSections:set];
    collectionView.collectionViewLayout = [[LineLayout alloc] init];
    [collectionView reloadData];
//    [self performSelector:@selector(reset) withObject:nil afterDelay:2];
}

- (void)reset {
    self.realAlbums = [self.albums mutableCopy];
    [self.collectionView reloadData];
    self.collectionView.collectionViewLayout = [[StackedPhotoLayout alloc] init];
}

@end

#pragma mark -
#pragma mark Application Setup
@interface DemoAppDelegate : NSObject <UIApplicationDelegate>
{
  UIWindow *window;
}
@end
@implementation DemoAppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [application setStatusBarHidden:YES];
	window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
	DemoCollectionViewController *vc = [[DemoCollectionViewController alloc] init];
    UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:vc];
    window.rootViewController = nav;
	[window makeKeyAndVisible];
    return YES;
}
@end

#pragma mark -
#pragma mark main
int main(int argc, char *argv[]) {
    @autoreleasepool {
        int retVal = UIApplicationMain(argc, argv, nil, @"DemoAppDelegate");
        return retVal;
    }
}