Ios 向已运行的UICollectionView添加更多图像

我在viewDidLoad中设置了一个UICollectionView，然后立即添加图像。当用户滚动到某一点时，我会尝试添加更多图像，但集合视图不会加载新图像

如何在scrollview中重新加载或添加更多图像

#pragma mark - New Retrieve
- (void) rwDataToPlist {

    // Step1: Get plist file path

    NSArray *sysPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory ,NSUserDomainMask, YES);

    NSString *documentsDirectory = [sysPaths objectAtIndex:0];

    NSString *filePath = [documentsDirectory stringByAppendingPathComponent:@"news.plist"];

    NSLog(@"Plist File Path: %@", filePath);

    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {

         stuff = [[NSArray alloc] initWithContentsOfFile:filePath];
        //NSLog(@"Stuff %@", stuff);
        [self sortRetrievedData];
     } else {


     }


}

-(void)sortRetrievedData {
    titles = [stuff valueForKey:kKeyTitle];
    thumbMediaUrl = [stuff valueForKey:kKeyThumbUrl];
    thumbWidth = [stuff valueForKey:kKeyThumbWidth];
    thumbHeight = [stuff valueForKey:kKeyThumbHeight];

    for(NSArray *array in titles) {
        for (NSArray *realArray in array) {
            titles = realArray;
        }
    }
    for(NSArray *array in thumbMediaUrl) {
        for(NSDictionary *dict in array) {
            thumbMediaUrl = dict;
        }
    }
    for(NSArray *array in thumbWidth) {
        for(NSDictionary *dict in array) {
            thumbWidth = dict;
        }
    }
    for(NSArray *array in thumbHeight) {
        for(NSDictionary *dict in array) {
            thumbHeight = dict;
        }
    }
}

#pragma mark - Collection View
#pragma mark - Display Collection 
-(void)displayCollection {
    UIColor *myColor = [UIColor colorWithRed:(245.0 / 255.0) green:(245.0 / 255.0) blue:(245.0 / 255.0) alpha: 1];

    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGSize screenSize = screenBound.size;
    CGFloat screenWidth = screenSize.width;
    CGFloat screenHeight = screenSize.height;
    self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    CGRect locOfScree = CGRectMake(0, 64, screenWidth, screenHeight - 44);

    UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
    imageDisplayer = [[UICollectionView alloc] initWithFrame:locOfScree collectionViewLayout:layout];
    [imageDisplayer setDataSource:self];
    [imageDisplayer setDelegate:self];

    UINib *nib = [UINib nibWithNibName:@"CollectionViewCell" bundle:nil];
    [imageDisplayer registerNib:nib forCellWithReuseIdentifier:CellIdentifier];
    [imageDisplayer setBackgroundColor:myColor];

    [self.view insertSubview:imageDisplayer belowSubview:navBar];
    //[self.view addSubview:imageDisplayer];
}

#pragma mark - Setup

- (void)setupData
{
    self.imageURLStrings = [NSMutableArray array];

    // Save image to docs directory so we can get a nice URL
    // Not sure how to get the URL from an asset catalog off the top of my head

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:@"greyBurger.png"];

    UIImage *image = [UIImage imageNamed:@"greyBurger"];
    NSData *data = UIImagePNGRepresentation(image);
    [data writeToFile:path atomically:YES];

    // Populate our imageURLStrings array with many paths

    for (NSInteger i = 0; i < NumberOfImages; i++)
    {
        [self.imageURLStrings addObject:path];
        //NSLog(@"Path %@", path);
    }
}

- (void)setupCollectionView
{
    UINib *nib = [UINib nibWithNibName:@"CollectionViewCell" bundle:nil];
    [self.collectionView registerNib:nib forCellWithReuseIdentifier:CellIdentifier];
}

#pragma mark - UICollectionView Datasource

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    //return [self.imageURLStrings count];
    return [titles count];
    //return 2;

}



- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CollectionViewCell *cell = (CollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];


    //NSLog(@"CELL FOR COUNT:%lu", [titles count]);
    NSString *title = [titles objectAtIndex:indexPath.row];
    cell.backgroundColor = [UIColor whiteColor];
    NSString *imageUrl = [thumbMediaUrl objectForKey:title];
    NSURL *thumbUrl = [NSURL URLWithString:imageUrl];
    UIImageView *imageView = [[UIImageView alloc] init];
    NSData *imageData = [NSData dataWithContentsOfURL:thumbUrl];
    imageView.image = [UIImage imageWithData:imageData];

    cell.backgroundView = imageView;
    cell.layer.shouldRasterize = YES;
    cell.layer.rasterizationScale = [UIScreen mainScreen].scale;
    //cell.frame = CGRectMake(0, 0, 100, 100);

    //cell.imageURLString = [self.imageURLStrings objectAtIndex:indexPath.item];

    return cell;
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGSize screenSize = screenBound.size;
    CGFloat screenWidth = screenSize.width;

    NSString *title = [titles objectAtIndex:indexPath.row];
    float width = [[thumbWidth objectForKey:title] floatValue];
    float height = [[thumbHeight objectForKey:title] floatValue];
    float imageWidth = (screenWidth / 2) - 3;
    float scale = imageWidth / width;
    float imageHeight = height * scale;
    CGSize imageSize = CGSizeMake(imageWidth, imageHeight);


    return imageSize;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    return 2.0;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 2.0;
}

// Layout: Set Edges
- (UIEdgeInsets)collectionView:
(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    // return UIEdgeInsetsMake(0,8,0,8);  // top, left, bottom, right
    return UIEdgeInsetsMake(0,0,0,0);  // top, left, bottom, right
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray* attributesToReturn = [self layoutAttributesForElementsInRect:rect];
    for (UICollectionViewLayoutAttributes* attributes in attributesToReturn)
    {
        if (nil == attributes.representedElementKind)
        {
            NSIndexPath* indexPath = attributes.indexPath;
            attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
        }
    }
    return attributesToReturn;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
     UICollectionViewLayoutAttributes* currentItemAttributes = [self layoutAttributesForItemAtIndexPath:indexPath];

    if (indexPath.item < numColumns){
        CGRect f = currentItemAttributes.frame;
        f.origin.y = 0;
        currentItemAttributes.frame = f;
        return currentItemAttributes;
    }
    NSIndexPath* ipPrev = [NSIndexPath indexPathForItem:indexPath.item-numColumns inSection:indexPath.section];
    CGRect fPrev = [self layoutAttributesForItemAtIndexPath:ipPrev].frame;
    CGFloat YPointNew = fPrev.origin.y + fPrev.size.height + 10;
    CGRect f = currentItemAttributes.frame;
    f.origin.y = YPointNew;
    currentItemAttributes.frame = f;
    return currentItemAttributes;
}

---

一些建议/问题：

由于不知道您的特定问题的限制，听起来您试图显示一些类似于网格的图像，并在用户滚动超过某个点时加载图像的“下一页”。看起来UITableView或UICollectionView是一种更合适的机制来完成您试图做的事情。这两个类都将处理图像的延迟加载、通过正确配置的数据源进行分页、自动调整contentSize，并且将在没有主线程冻结的情况下快速运行。它们也基于MVC设计模式，可能会澄清上面代码中的一些设计

加载更多图像时，UI/滚动冻结的原因可能是从磁盘读取用户默认值和图像数据本身。磁盘操作可能很昂贵，尤其是一次操作很多磁盘。如果您必须以这种方式加载元数据和图像文件，请考虑通过GCD的代码> DeXCHCHYASYNC/<代码>在后台线程上进行此处理。

第二组图像未出现的原因可能是图像帧或scrollView内容大小计算错误。通过在ScLoVIEW中添加一系列有色UIVIEW而不是UIIVIEVIEW来考虑调试，并考虑将Cordsisi.Head硬编码为比您需要的大很多的东西。另外，您是否记录了图像帧和内容大小以确保它们匹配

编辑：

这里有一个链接，指向一个使用UICollectionView和后台线程从磁盘读取UIImage数据的快速示例项目（由于使用UICollectionView，不再需要该线程）：

---

如果您有任何疑问，请告诉我，希望我没有完全偏离您的目标。

随着iOS6本身的启动，苹果为UICollectionView引入了iOS6。您可以使用UICollectionView和下拉式刷新来实现您的目标。它看起来像UtableView拉到底刷新

以下是UIcollectionView的一些参考：

创建UICollectionView后，需要为UICollectionView添加PulltoBottom刷新，如以下代码所示：

-(void)viewWillAppear:(BOOL)animated
{

[self.collectionView.infiniteScrollingView setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleWhite];
[self.collectionView addInfiniteScrollingWithActionHandler:^{
    ////(@"Infinitescroll");







    @try {
        int64_t delayInSeconds = 2.0;
        dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
        dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
            //[self.dataSource addObjectsFromArray:tmp];
            [self.collectionView performBatchUpdates:^{


            } completion:nil];
            [self.collectionView.infiniteScrollingView stopAnimating];
        });
    }
    @catch (NSException *exception) {

    }





}];

[super viewWillAppear:animated];
}

对于以下代码，您必须添加一些文件：

---

我使用了前两个答案中建议的UICollectionView，并添加到其中，以允许我想要的图像间距

我的代码：

#pragma mark - Collection View
#pragma mark - Display Collection 
-(void)displayCollection {
    UIColor *myColor = [UIColor colorWithRed:(245.0 / 255.0) green:(245.0 / 255.0) blue:(245.0 / 255.0) alpha: 1];

    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGSize screenSize = screenBound.size;
    CGFloat screenWidth = screenSize.width;
    CGFloat screenHeight = screenSize.height;
    self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    CGRect locOfScree = CGRectMake(0, 44, screenWidth, screenHeight - 44);

    CHTCollectionViewWaterfallLayout *layout = [[CHTCollectionViewWaterfallLayout alloc] init];

    layout.sectionInset = UIEdgeInsetsMake(2, 2, 2, 2);
    layout.headerHeight = 0;
    layout.footerHeight = 0;
    layout.minimumColumnSpacing = 2;
    layout.minimumInteritemSpacing = 2;
    //UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
    imageDisplayer = [[UICollectionView alloc] initWithFrame:locOfScree collectionViewLayout:layout];
    imageDisplayer.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;

    [imageDisplayer setDataSource:self];
    [imageDisplayer setDelegate:self];

    UINib *nib = [UINib nibWithNibName:@"CollectionViewCell" bundle:nil];
    [imageDisplayer registerNib:nib forCellWithReuseIdentifier:CellIdentifier];
    [imageDisplayer setBackgroundColor:myColor];

    [self.view insertSubview:imageDisplayer belowSubview:navBar];
    //[self.view addSubview:imageDisplayer];

    imageDisplayer = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    imageDisplayer.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    imageDisplayer.dataSource = self;
    imageDisplayer.delegate = self;
    imageDisplayer.backgroundColor = [UIColor whiteColor];
    [imageDisplayer registerClass:[CHTCollectionViewWaterfallCell class]
        forCellWithReuseIdentifier:CellIdentifier];
}

#pragma mark - Setup
- (void)setupCollectionView
{
    UINib *nib = [UINib nibWithNibName:@"CollectionViewCell" bundle:nil];
    [self.collectionView registerNib:nib forCellWithReuseIdentifier:CellIdentifier];
}

#pragma mark - UICollectionView Datasource

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    //return [self.imageURLStrings count];
    return [titles count];
    //return 2;

}



- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    /*
    CollectionViewCell *cell = (CollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
    */
    CHTCollectionViewWaterfallCell *cell =
    (CHTCollectionViewWaterfallCell *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier
                                                                                forIndexPath:indexPath];

    NSString *title = [titles objectAtIndex:indexPath.row];
    cell.backgroundColor = [UIColor whiteColor];
    NSString *imageUrl = [thumbMediaUrl objectForKey:title];
    NSURL *thumbUrl = [NSURL URLWithString:imageUrl];
    UIImageView *imageView = [[UIImageView alloc] init];
    NSData *imageData = [NSData dataWithContentsOfURL:thumbUrl];
    imageView.image = [UIImage imageWithData:imageData];

    cell.backgroundView = imageView;
    cell.layer.shouldRasterize = YES;
    cell.layer.rasterizationScale = [UIScreen mainScreen].scale;
    return cell;

}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGSize screenSize = screenBound.size;
    CGFloat screenWidth = screenSize.width;

    NSString *title = [titles objectAtIndex:indexPath.row];
    float width = [[thumbWidth objectForKey:title] floatValue];
    float height = [[thumbHeight objectForKey:title] floatValue];
    float imageWidth = (screenWidth / 2) - 3;
    float scale = imageWidth / width;
    float imageHeight = height * scale;
    CGSize imageSize = CGSizeMake(imageWidth, imageHeight);


    return imageSize;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    return 2.0;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 2.0;
}

// Layout: Set Edges
- (UIEdgeInsets)collectionView:
(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    // return UIEdgeInsetsMake(0,8,0,8);  // top, left, bottom, right
    return UIEdgeInsetsMake(0,0,0,0);  // top, left, bottom, right
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray* attributesToReturn = [self layoutAttributesForElementsInRect:rect];
    for (UICollectionViewLayoutAttributes* attributes in attributesToReturn)
    {
        if (nil == attributes.representedElementKind)
        {
            NSIndexPath* indexPath = attributes.indexPath;
            attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
        }
    }
    return attributesToReturn;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
     UICollectionViewLayoutAttributes* currentItemAttributes = [self layoutAttributesForItemAtIndexPath:indexPath];

    if (indexPath.item < numColumns){
        CGRect f = currentItemAttributes.frame;
        f.origin.y = 0;
        currentItemAttributes.frame = f;
        return currentItemAttributes;
    }
    NSIndexPath* ipPrev = [NSIndexPath indexPathForItem:indexPath.item-numColumns inSection:indexPath.section];
    CGRect fPrev = [self layoutAttributesForItemAtIndexPath:ipPrev].frame;
    CGFloat YPointNew = fPrev.origin.y + fPrev.size.height + 10;
    CGRect f = currentItemAttributes.frame;
    f.origin.y = YPointNew;
    currentItemAttributes.frame = f;
    return currentItemAttributes;
}

#pragma标记-集合视图
#pragma标记-显示集合
-（作废）收款{
UIColor*myColor=[UIColor color withred:（245.0/255.0）green:（245.0/255.0）blue:（245.0/255.0）alpha:1]；
CGRect屏幕绑定=[[UIScreen mainScreen]边界]；
CGSize screenSize=screensbound.size；
CGFloat screenWidth=屏幕大小.width；
CGFloat屏幕高度=屏幕尺寸.height；
self.view=[[UIView alloc]initWithFrame:[[UIScreen mainScreen]bounds]]；
CGRect LOCOFFSCREE=CGRectMake（0,44，屏幕宽度，屏幕高度-44）；
chtcollectionviewwaterwalllayout*layout=[[chtcollectionviewwaterwalllayout alloc]init]；
layout.sectionInset=UIEdgeInsetsMake（2,2,2,2）；
layout.headerHeight=0；
layout.footerHeight=0；
布局。最小列间距=2；
layout.minimumInteritemSpacing=2；
//UICollectionViewFlowLayout*布局=[[UICollectionViewFlowLayout alloc]init]；
imageDisplayer=[[UICollectionView alloc]initWithFrame:locofScreeCollectionViewLayout:layout]；
imageDisplayer.autoresizingMask=UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth；
[imageDisplayer setDataSource:self]；
[imageDisplayer setDelegate:self]；
UINib*nib=[UINib-nibWithNibName:@“CollectionViewCell”捆绑包：nil]；
[imageDisplayer RegisterInB:nib forCellWithReuseIdentifier:CellIdentifier]；
[图像显示器setBackgroundColor:myColor]；
[self.view insertSubview:imageDisplayer below子视图：导航栏]；
//[self.view addSubview:imageDisplayer]；
imageDisplayer=[[UICollectionView alloc]initWithFrame:self.view.bounds collectionViewLayout:layout]；
imageDisplayer.autoresizingMask=UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth；
imageDisplayer.dataSource=self；
imageDisplayer.delegate=self；
imageDisplayer.backgroundColor=[UIColor whiteColor]；
[imageDisplayer注册表类：[chtCollectionViewWaterCallCell类]
forCellWithReuseIdentifier:CellIdentifier]；
}
#pragma标记-设置
-（无效）setupCollectionView
{
UINib*nib=[UINib-nibWithNibName:@“CollectionViewCell”捆绑包：nil]；
[self.collectionView registerNib:nib forCellWithReuseIdentifier:CellIdentifier]；
}
#pragma标记-UICollectionView数据源
-（NSInteger）collectionView:（UICollectionView*）collectionView项目编号截面：（NSInteger）截面
{
//返回[self.imageUrlString计数]；
返回[标题计数]；
//返回2；
}
-（UICollectionViewCell*）collectionView:（UICollectionView*）collectionView cellForItemAtIndexPath:（NSIndexPath*）indexPath
{
/*
CollectionViewCell*cell=（CollectionViewCell*）[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath]；
*/
CHTCollectionViewWaterWallCell*单元格=
（CHTCollectionViewWaterWallCell*）[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier
forIndexPath:indexPath]；
NSString*title=[titles-objectAtIndex:indexath.row]；
cell.backgroundColor=[UIColor whiteColor]；
NSString*imageUrl=[thumbMediaUrl objectForKey:title]；
NSURL*thumbUrl=[NSURL URLWithString:imageUrl]；
UIImageView*ima
#pragma mark - Collection View
#pragma mark - Display Collection 
-(void)displayCollection {
    UIColor *myColor = [UIColor colorWithRed:(245.0 / 255.0) green:(245.0 / 255.0) blue:(245.0 / 255.0) alpha: 1];

    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGSize screenSize = screenBound.size;
    CGFloat screenWidth = screenSize.width;
    CGFloat screenHeight = screenSize.height;
    self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    CGRect locOfScree = CGRectMake(0, 44, screenWidth, screenHeight - 44);

    CHTCollectionViewWaterfallLayout *layout = [[CHTCollectionViewWaterfallLayout alloc] init];

    layout.sectionInset = UIEdgeInsetsMake(2, 2, 2, 2);
    layout.headerHeight = 0;
    layout.footerHeight = 0;
    layout.minimumColumnSpacing = 2;
    layout.minimumInteritemSpacing = 2;
    //UICollectionViewFlowLayout *layout=[[UICollectionViewFlowLayout alloc] init];
    imageDisplayer = [[UICollectionView alloc] initWithFrame:locOfScree collectionViewLayout:layout];
    imageDisplayer.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;

    [imageDisplayer setDataSource:self];
    [imageDisplayer setDelegate:self];

    UINib *nib = [UINib nibWithNibName:@"CollectionViewCell" bundle:nil];
    [imageDisplayer registerNib:nib forCellWithReuseIdentifier:CellIdentifier];
    [imageDisplayer setBackgroundColor:myColor];

    [self.view insertSubview:imageDisplayer belowSubview:navBar];
    //[self.view addSubview:imageDisplayer];

    imageDisplayer = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    imageDisplayer.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    imageDisplayer.dataSource = self;
    imageDisplayer.delegate = self;
    imageDisplayer.backgroundColor = [UIColor whiteColor];
    [imageDisplayer registerClass:[CHTCollectionViewWaterfallCell class]
        forCellWithReuseIdentifier:CellIdentifier];
}

#pragma mark - Setup
- (void)setupCollectionView
{
    UINib *nib = [UINib nibWithNibName:@"CollectionViewCell" bundle:nil];
    [self.collectionView registerNib:nib forCellWithReuseIdentifier:CellIdentifier];
}

#pragma mark - UICollectionView Datasource

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    //return [self.imageURLStrings count];
    return [titles count];
    //return 2;

}



- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    /*
    CollectionViewCell *cell = (CollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
    */
    CHTCollectionViewWaterfallCell *cell =
    (CHTCollectionViewWaterfallCell *)[collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier
                                                                                forIndexPath:indexPath];

    NSString *title = [titles objectAtIndex:indexPath.row];
    cell.backgroundColor = [UIColor whiteColor];
    NSString *imageUrl = [thumbMediaUrl objectForKey:title];
    NSURL *thumbUrl = [NSURL URLWithString:imageUrl];
    UIImageView *imageView = [[UIImageView alloc] init];
    NSData *imageData = [NSData dataWithContentsOfURL:thumbUrl];
    imageView.image = [UIImage imageWithData:imageData];

    cell.backgroundView = imageView;
    cell.layer.shouldRasterize = YES;
    cell.layer.rasterizationScale = [UIScreen mainScreen].scale;
    return cell;

}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CGRect screenBound = [[UIScreen mainScreen] bounds];
    CGSize screenSize = screenBound.size;
    CGFloat screenWidth = screenSize.width;

    NSString *title = [titles objectAtIndex:indexPath.row];
    float width = [[thumbWidth objectForKey:title] floatValue];
    float height = [[thumbHeight objectForKey:title] floatValue];
    float imageWidth = (screenWidth / 2) - 3;
    float scale = imageWidth / width;
    float imageHeight = height * scale;
    CGSize imageSize = CGSizeMake(imageWidth, imageHeight);


    return imageSize;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    return 2.0;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 2.0;
}

// Layout: Set Edges
- (UIEdgeInsets)collectionView:
(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    // return UIEdgeInsetsMake(0,8,0,8);  // top, left, bottom, right
    return UIEdgeInsetsMake(0,0,0,0);  // top, left, bottom, right
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray* attributesToReturn = [self layoutAttributesForElementsInRect:rect];
    for (UICollectionViewLayoutAttributes* attributes in attributesToReturn)
    {
        if (nil == attributes.representedElementKind)
        {
            NSIndexPath* indexPath = attributes.indexPath;
            attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
        }
    }
    return attributesToReturn;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
     UICollectionViewLayoutAttributes* currentItemAttributes = [self layoutAttributesForItemAtIndexPath:indexPath];

    if (indexPath.item < numColumns){
        CGRect f = currentItemAttributes.frame;
        f.origin.y = 0;
        currentItemAttributes.frame = f;
        return currentItemAttributes;
    }
    NSIndexPath* ipPrev = [NSIndexPath indexPathForItem:indexPath.item-numColumns inSection:indexPath.section];
    CGRect fPrev = [self layoutAttributesForItemAtIndexPath:ipPrev].frame;
    CGFloat YPointNew = fPrev.origin.y + fPrev.size.height + 10;
    CGRect f = currentItemAttributes.frame;
    f.origin.y = YPointNew;
    currentItemAttributes.frame = f;
    return currentItemAttributes;
}