-2

could you please give me some advices please. I've been struggled for days.

My goal is implement continuous scrolling to show pages from document. Each page is controlled by a viewController. And user should be able zoom in and out. Should i do it from scratch with scrollView or collectionView? which is better and more memory efficient?

Or there are any off-the-shelf solution for this? (i've searched in Github without success, UIPageViewController is definitive not a solution because it doesn't allow continuous scrolling and only show a whole page)

Thank you very much

Image: example continuous scrolling

Brew Master
  • 457
  • 3
  • 13

1 Answers1

0

A collection view works just fine for continuous scrolling, and makes efficient use of memory. (Cells are recycled.) If the total contents of your scrolling area are too much to fit into memory you will want to load each page's contents into memory as it scrolls into view, and release it when it scrolls off. (Perhaps have your model store file URLs to each page's contents, and save the page contents into the cell.)

As for zooming, the best way to do that depends on what you mean. If the contents are vector contents like a PDF, you could simply re-render the vector image as the user scrolls. If the contents are very high resolution images you might need to create a mipmapped tiled rendering framework, or use somebody else's. I've written my own mipmapped tiled rendering framework before. It's doable, but a lot of work.

(You take the original huge image and break it into smaller square tiles. You then render the original image into tiles at 50% scale and save those, and then 25%, and then 12.5%, etc, until you get to a size where a single image fills the screen.)

Duncan C
  • 128,072
  • 22
  • 173
  • 272
  • Thank you, i'm trying to implement it UICollectionView first. I tried to add ViewController to a cell like that: In cellForItemAt: `self.addChild(viewControllerForPage) viewControllerForPage.view.frame = cell.bounds cell.contentView.addSubview(viewControllerForPage.view) drawingViewController.didMove(toParent: self) return cell ` and then there are an error: "Terminating app due to uncaught exception 'CALayerInvalidGeometry', reason: 'CALayer position contains NaN" Don't know what i'm doing wrong but at least i can scroll continuously through cells – Brew Master Dec 30 '20 at 19:10
  • Post a new question with that specific problem as the subject, and include a link to a sample project that reproduces the crash. It's very hard to look at code in an SO comment and tell what's wrong. – Duncan C Dec 30 '20 at 21:27