<UICollectionViewDelegate, UICollectionViewDataSource,CHTCollectionViewDelegateWaterfallLayout>

CHTCollectionViewWaterfallLayout *layout = [[CHTCollectionViewWaterfallLayout alloc] init];
    self.collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 20, 320, 460) collectionViewLayout:layout];
    layout.sectionInset = UIEdgeInsetsMake(10, 15, 10, 15);//上下左右的間距
    layout.minimumColumnSpacing = 5; //左右cell的間距
    layout.minimumInteritemSpacing = 5;//上下cell的間距
    layout.columnCount = 3;    //3列， 根據列數，間距等，使每個cell的寬度固定
    layout.headerHeight = 200; //類似tableView的heardview的高度
    self.collectionView.dataSource = self;
    self.collectionView.delegate = self;
    
    //註冊cell
    [self.collectionView registerClass:[WaterFallCell class] forCellWithReuseIdentifier:CELL_IDENTIFIER];
    //註冊headerview
    [self.collectionView registerClass:[HeadView class] forSupplementaryViewOfKind:CHTCollectionElementKindSectionHeader withReuseIdentifier:HEADER_IDENTIFIER];
    //註冊footerView   CHTCollectionElementKindSectionFooter
    self.collectionView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    
    
    self.collectionView.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:self.collectionView];
 

#pragma mark - UICollectionViewDataSource
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 1;
}
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    UICollectionReusableView *reusableView = nil;
    if ([kind isEqualToString:CHTCollectionElementKindSectionHeader]) {
        reusableView = (HeadView*)[collectionView dequeueReusableSupplementaryViewOfKind:kind
                                                          withReuseIdentifier:HEADER_IDENTIFIER
                                                                 forIndexPath:indexPath];

    }
    return reusableView;
}


- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    NSLog(@"self.imageList = %d", self.imageList.count);
    return self.imageList.count;
}

- (UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    WaterFallCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:CELL_IDENTIFIER forIndexPath:indexPath];
    cell.layer.masksToBounds = YES;
    cell.layer.cornerRadius = 5.0f;
    
    [cell.imageView sd_setImageWithURL:[NSURL URLWithString:[self.imageList objectAtIndex:indexPath.row]]];
    return cell;
}

#pragma mark - UICollectionViewDelegate
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSLog(@"indexs = %d", indexPath.row);
}
#pragma mark - CHTCollectionViewDelegateWaterfallLayout
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    return [self.cellSizes[indexPath.item] CGSizeValue];
}