从其他类调用collectionview中的下一个图像

Question

I built an app that fetch all the photos from Instagram user via Instagram API and show them ordered in CollectionView.

Now, when the user tap on a photo the photo will open in a UIView to show that image - basically the user can pinch to zoom and other options that can't be in the Instagram app.

What I'm trying to do is - swipe the image to move to the next image. I thought about using ScrollView which is not a big deal.

THE PROBLEM IS that I don't know how to call the next photo in the collection view.

Answer 1

just store selected index path. Next photo will be next index path.

Example: self.selectedIndexPath = indexPath - save

Then get next index path or nil (if not exist):

func nextIndexPath() -> NSIndexPath? {
  if collectionView.numberOfItemsInSection(selectedIndexPath.section) > selectedIndexPath.item {
      return NSIndexPath(forItem: selectedIndexPath.item + 1, inSection: selectedIndexPath.section)
  }
  return nil
}

Then you could use it to get next photo, something like this:

if let indexPath = nextIndexPath() {
  let photo = photos[indexPath.item]
}

PS item is the same as row , but for CollectionView, because row wrong name for it. So it's preferable to use item in collection views

Answer 2

You can use delegation something like this, have your view displaying the image call nextPhoto() when need an the collection view will supply.

        struct Photo {
            var image:UIImage?
        }

        class CustomCollectionView: UICollectionViewController{
            var dataSource:[Photo]! = []
            var selectedIndex:NSIndexPath!

            override func viewDidLoad() {
                super.viewDidLoad()
            }
        }

        extension CustomCollectionView: UpdatePhoto {

            func nextPhoto() -> Photo?{
                let nextIndex = selectedIndex.row + 1
                 // update selected index

                selectedIndex = NSIndexPath(forRow: nextIndex, inSection: 0)
                return dataSource[selectedIndex.row];
            }

            func previousPhoto() -> Photo? {
                let previousIndex = selectedIndex.row - 1
                // update selected index
                selectedIndex = NSIndexPath(forRow: previousIndex , inSection: 0)
                return dataSource[selectedIndex.row];
            }
        }

        protocol UpdatePhoto {
            func nextPhoto() -> Photo?
            func previousPhoto() -> Photo?
        }
    class PhotoDisplayingView:UIView{
        var photo:Photo
        var delegate:UpdatePhoto?

        required init(photo:Photo){
            self.photo = photo
            super.init(frame: CGRect(origin: CGPointZero, size: photo.image!.size))
        }

        required init?(coder aDecoder: NSCoder) {
                fatalError("init(coder:) has not been implemented")
            }
        }
     }

You'll do something like this when handling the gesture var nextImage = delegate.nextPhoto()