Learn how to implement a cool effect so that as the user scrolls the next cell snaps into place as it becomes the featured cell.
Using UltraVisual demo on iOS9 for months and it runs fine, but running in Xcode 8 on iOS10 (Deployment Target still 8.2) and receiving error during scroll
2016-09-21 15:01:55.510438 Ultravisual[4159:1309927] *** Assertion failure in -[UICollectionViewData layoutAttributesForItemAtIndexPath:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3599.6/UICollectionViewData.m:709
2016-09-21 15:01:55.516660 Ultravisual[4159:1309927] *** Terminating app due to uncaught exception ‘NSInternalInconsistencyException’, reason: ‘no UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath: <NSIndexPath: 0xc000000001600016> {length = 2, path = 0 - 11}’
Identified the fix needed. Change UltraVisualLayout to inherit UICollectionViewFlowLayout instead of UICollectionViewLayout. After that works great in iOS10.
That almost fixes it… I had to play with the z index as well to prevent a semi strange flicker.
override func prepareLayout() {
cache.removeAll(keepCapacity: false)
let standardHeight = UltravisualLayoutConstants.Cell.standardHeight
let featuredHeight = UltravisualLayoutConstants.Cell.featuredHeight
var frame = CGRectZero
var y: CGFloat = 0
for item in 0..<numberOfItems {
let indexPath = NSIndexPath(forItem: item, inSection: 0)
let attributes = UICollectionViewLayoutAttributes(forCellWithIndexPath: indexPath)
/* Important because each cell has to slide over the top of the previous one */
/* Initially set the height of the cell to the standard height */
attributes.zIndex = numberOfItems - item
var height = standardHeight
if indexPath.item == featuredItemIndex {
/* The featured cell */
attributes.zIndex = 0
let yOffset = standardHeight * nextItemPercentageOffset
y = collectionView!.contentOffset.y - yOffset
height = featuredHeight
} else if indexPath.item == (featuredItemIndex + 1) && indexPath.item != numberOfItems {
attributes.zIndex = item
/* The cell directly below the featured cell, which grows as the user scrolls */
let maxY = y + standardHeight
height = standardHeight + max((featuredHeight - standardHeight) * nextItemPercentageOffset, 0)
y = maxY - height
}
frame = CGRect(x: 0, y: y, width: width, height: height)
attributes.frame = frame
cache.append(attributes)
y = CGRectGetMaxY(frame)
}
}
Actually, the only change you have to make is to implement layoutAttributesForItem(at:) which is required but was left out of the project. So, add:
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
return cache[indexPath.item]
}
That will clear the crash and should fix the flicker problems as well.
Anybody can some idea to how to do in Android ?
How could we do the cell resizing with images loaded from an url and not stored in de bundle?
How could we add the stretchy header from video 6 to this custom layout
Hello,
I’ve successfully used Custom Collection View Layouts. I watched this series more as a refresher. There is perhaps one minor issue. If I run Instruments on my app it points to a memory leak in the vicinity of prepare(). I downloaded the finished app from lesson 10 and, sure enough, it shows a memory leak int the same area; in or around prepare(). I’ve spent an hour or so looking at the code and can’t spot any leaks.
It is easy to see: just profile the app with Leaks and you’ll see it shortly after the app launches.
Any ideas what could be causing it?
I love the topic of this course, but I feel like I only understand about 25% what’s covered. I wish there was more explanation, and or additional resources provided where I can learn about what’s happening and why, instead of just typing what the instructor types and hoping that it works…
