func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
    1. 设置photoModels
    func setPhoto() -> [PhotoModel] {
        var photos: [PhotoModel] = []
        for (index, image) in images.enumerate() {
	        //  这个方法只能返回可见的cell, 如果不可见, 返回值为nil
            let cell = collectionView.cellForItemAtIndexPath(NSIndexPath(forRow: index, inSection: 0)) as? TestCell
            let sourceView = cell?.imageView
			// 在这里设置本地图片的photoModel, 注意指定的sourceImageView是图片的imageView,用来执行动画和设置初始图片
            let photoModel = PhotoModel(localImage: image, sourceImageView: sourceView, description: nil)
            photos.append(photoModel)
        }
        return photos
    }
    
    // 2. 初始化PhotoBrowser
    let photoBrowser = PhotoBrowser(photoModels: setPhoto())
    // 3. 设置初始的页数
    photoBrowser.showWithBeginPage(indexPath.row)
}

    func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
    1. 设置photoModels
    func setPhoto() -> [PhotoModel] {
        var photos: [PhotoModel] = []
        for (index, photoURLString) in photosURLString.enumerate() {
            // 这个方法只能返回可见的cell, 如果不可见, 返回值为nil
            let cell = collectionView.cellForItemAtIndexPath(NSIndexPath(forRow: index, inSection: 0)) as? TestCell
            let sourceView = cell?.imageView
            
            // 这里设置网络图片的photoModel 注意指定的sourceImageView是图片的imageView,用来执行动画和设置初始图片
            let photoModel = PhotoModel(imageUrlString: photoURLString, sourceImageView: sourceView, description: nil)
            photos.append(photoModel)
        }
        return photos
    }
    
    // 2. 初始化PhotoBrowser
    let photoBrowser = PhotoBrowser(photoModels: setPhoto())
    // 3. 设置初始的页数
    photoBrowser.showWithBeginPage(indexPath.row)
}

    func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
    1. 设置photoModels
    func setPhoto() -> [PhotoModel] {
        var photos: [PhotoModel] = []
        for photoURLString in photosURLString {
            // 初始化不设置sourceImageView,也可以设置, 如果sourceImageView是不需要动态改变的, 那么推荐不需要代理设置sourceImageView
            // 而在代理方法中动态更新,将会覆盖原来设置的sourceImageView
            let photoModel = PhotoModel(imageUrlString: photoURLString, sourceImageView: nil, description: nil)
            photos.append(photoModel)
        }
        return photos
    }
    // 2. 初始化PhotoBrowser
    let photoBrowser = PhotoBrowser(photoModels: setPhoto())
    // 3. 指定代理
    photoBrowser.delegate = self
    // 4. 设置初始的页数
    photoBrowser.showWithBeginPage(indexPath.row)
}   

// 正在展示的页
// 因为通过 collectionView.cellForItemAtIndexPath(currentIndexPath)
// 这个方法只能获取到当前显示在collectionView中的cell, 否则返回nil,
// 所以如果是在浏览图片的时候的页数对应的currentIndexPath已经不在collectionView的可见cell范围内
// 返回的将是nil, 就不能准确的获取到 sourceImageView 
// 故在每次显示图片的时候判断如果对应的sourceImageView cell已经不可见
// 那么就更新collectionView的位置, 滚动到相应的cell
// 当然更新collectionView位置的方法很多, 这里只是示例
func photoBrowserDidDisplayPage(currentPage: Int, totalPages: Int) {
    let visibleIndexPaths = collectionView.indexPathsForVisibleItems()
    
    let currentIndexPath = NSIndexPath(forRow: currentPage, inSection: 0)
    if !visibleIndexPaths.contains(currentIndexPath) {
        collectionView.scrollToItemAtIndexPath(currentIndexPath, atScrollPosition: .Top, animated: false)
    }
}
// 获取动态改变的sourceImageView
func sourceImageViewForCurrentIndex(index: Int) -> UIImageView? {
    
    let currentIndexPath = NSIndexPath(forRow: index, inSection: 0)
    
    let cell = collectionView.cellForItemAtIndexPath(currentIndexPath) as? TestCell
    let sourceView = cell?.imageView
    return sourceView
}