拿到点击事件，然后你显示对应的UI

 func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
    let url = thumbnailFileURLS[indexPath.item]
    if UIApplication.sharedApplication().canOpenURL(url) {
        UIApplication.sharedApplication().openURL(url)
    }
}