UICollectionView horizontal paging with space between pages

问题

I'm looking for a way to replace the native UIPageViewController horizontal paging with a UICollectionView.

so far i did the following:

let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .horizontal
layout.itemSize = collectionView.frame.size
layout.minimumLineSpacing = 0
layout.minimumInteritemSpacing = 10

collectionView.setCollectionViewLayout(layout, animated: false)
collectionView.isPagingEnabled = true
collectionView.alwaysBounceVertical = false

this works fine and i get an horizontal paging effect.

Now i want to add horizontal space between the pages (like u will do with UIPageViewControllerOptionInterPageSpacingKey on UIPageViewController)

so far i couldn't fine a way to add the spaces without damaging the paging effect. im looking for the same behavior as with the UIPageViewController: the cell should fill the entire screen width, and the space between the cells should only be visible when switching a page.

回答1:

Solution one:

1. collectionView.isPagingEnabled = false
2. add a minimumLineSpacing for the distance between pages
3. implement targetContentOffsetForProposedContentOffset:withScrollingVelocity: to move the contentOffset to the closest page. You can calculate the page with simple math based on your itemSize and minimumLineSpacing, but it can take a little work to get it right.

Solution Two:

1. collectionView.isPagingEnabled = true
2. add a minimumLineSpacing for the distance between pages
3. the paging size is based on the bounds of the collectionView. So make the collectionView larger then then screenSize. For example, if you have a minimumLineSpacing of 10 then set the frame of the collectionView to be {0,-5, width+10, height}
4. set a contentInset equal to the minimumLineSpacing to make the first and last item appear correctly.

回答2:

• By default, UICollectionViewFlowLayout's minimumLineSpacing is 10.0, when collectionView's item is horizontally filled (itemSize.width = collectionView.bounds.width) and collectionView is paging enabled, greater than zero 'minimumLineSpacing' will cause an unintended performance: start from second page, every page has a gap which will be accumulated by page number.
• It seems that we can expand collectionView's width by 'minimumLineSpacing' to fix this problem. But pratice negates this solution: When there are tow pages or more, collectionView will not give the last one a 'lineSpacing', so it's 'contentSize' is not enough to show this page's content completely, which means if the 'minimumLineSpacing' were 10.0, the last page's end would overstep the collectionView's contentSize by 10.0.
• Finally, I use the following simple solution to insert a margin between every item (like UIScrollView's preformance): Expand every collectionViewItem's width by a fixed value 'pageSpacing' (such as 10.0), and expand the collectionView's width by the same value, too. And don't forget that, when layout collevtionViewCell's subviews, there's an additional spacing which is not for diplaying the real content.

Heres the code written in Swift 3.1, I'm sure it's easily understanding for you:

let pageSpacing: CGFloat = 10

class ViewController: UITableViewController {
     override func viewDidLoad() {
        super.viewDidLoad()

        let layout = UICollectionViewFlowLayout()
        layout.itemSize                = CGSize(width: view.frame.width + pageSpacing, height: view.frame.height)
        layout.scrollDirection         = .horizontal
        layout.minimumInteritemSpacing = 0
        layout.minimumLineSpacing      = 0

        let frame = CGRect(x: 0, y: 0, width: view.frame.width + pageSpacing, height: view.frame.height)
        let collectionView = UICollectionView(frame: frame, collectionViewLayout: layout)
        view.addSubview(collectionView)
    }
}

class MyCell: UICollectionViewCell {
    var fullScreenImageView = UIImageView()
    override func layoutSubviews() {
        super.layoutSubviews()
        fullScreenImageView.frame = CGRect(x: 0, y: 0, width: frame.width - pageSpacing, height: frame.height)
    }
}

Hope that can help you.

来源：https://stackoverflow.com/questions/42486960/uicollectionview-horizontal-paging-with-space-between-pages