iosuicollectionviewuicollectionviewcelluicollectionviewflowlayoutuicollectionviewdelegate

UICollectionViewCell width is bigger than what I set in sizeForItemAt

Width/height of my UICollectionView matches all available space.

I want to display two cells in one row (two columns)

So width of one cell should take half width of UICollectionView (collectionView.frame.width / 2)

So I programmatically change width of cell in function of UICollectionViewDelegateFlowLayout:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: collectionView.frame.width / 2.0, height: 150)
}

But visually width of cell is much bigger than collectionView.frame.width / 2.0 (tested on iPhone SE simulator)

So it takes more than half-width space of screen

Here I printed info about sizes:

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath)
    print("didSelectItemAt \(cell.frame.width), table width: \(collectionView.frame.width), item calc width: \(collectionView.frame.width / 2)")
}

didSelectItemAt cell width 187.5, table width: 375.0, half-width: 187.5

enter image description here

Why does it happen?

There is also an issue with margins but first I have to solve this one

Update

Though it works fine with iPhone 6s Simulator (I edited image to place two items in the first row to check if they fit):

enter image description here

So what is wrong with iPhone SE?

I don't want to find out that there can be the same issue with other iPhones or iPads too

Solution

  • 375.0 is the size of iPhone 6s and X, not iPhone SE which is 320.0

    The reason is there is a width constraint of collectionView which was set at iPhone 6s mode but later when switching to the SE simulator, this constraint was not updated.