Why are the constraints not working?

Question

Portrait mode

Landscape mode

Tab Bar implemented using UICollectionView (CV). In the CV I have added 4 items:

addSubview(collectionTab)
addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0":collectionTab]))
addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0":collectionTab]))

When I change the orientation the constraints are not working. Why? How can I fix it? I think the size of items is not recalculated when I change the view.

Size of items:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: frame.width/4, height: frame.height)
}

size of items func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize { return CGSize(width: frame.width/4, height: frame.height) } — maxim rad, Nov 17 '16 at 09:08
What is collectionTab? Is that the name of the UICollectionView? — Sajjon, Nov 17 '16 at 09:43

score 1 · Accepted Answer · edited May 23 '17 at 12:13

1

Try running invalidateLayout on the UICollectionViewLayout on your UICollectionView. Like this

override func viewWillLayoutSubviews {
    myCollectionView.collectionViewLayout.invalidateLayout()
}

edited May 23 '17 at 12:13

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answered Nov 17 '16 at 08:43

Sajjon

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When run this function? – maxim rad Nov 17 '16 at 09:10
Just implement this in your UIViewController, it gets called automatically – Sajjon Nov 17 '16 at 09:25
I think the size of items is not recalculated when I change the view – maxim rad Nov 17 '16 at 09:38
are you implementing `collectionView(_:layout:sizeForItemAt:)`? You should calculate item size there! – Sajjon Nov 17 '16 at 09:38
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize { return CGSize(width: frame.width/4, height: frame.height) } – maxim rad Nov 17 '16 at 09:42
Can you verify that the CollectionView gets a new frame after rotation? Please print the width and height of the CollectionView before and after rotation inside the viewWillLayoutSubviews method – Sajjon Nov 17 '16 at 10:03
@maximrad did you print the frames before and after rotation, what are the result? – Sajjon Nov 17 '16 at 13:37
Thanks very very much!! – maxim rad Nov 17 '16 at 13:52
override func viewWillLayoutSubviews() { tabBar.collectionTab.collectionViewLayout.invalidateLayout() } – maxim rad Nov 17 '16 at 13:53

Why are the constraints not working?

1 Answers1