Manipulate constraint to move a view to the bottom of the screen - ios

Question

I have a collection view that is aligned horizontally and vertically in the container. When a user selects the cell I want that collection view to move to the bottom of the screen, and then I want a UIView to appear right above the collection view.
Below is how my collection view is constrained.
So the way I went about this was making the bottom space constraint an outlet in my code file.
#IBOutlet var collectionViewBottomConstraint: NSLayoutConstraint!
Then when a user tapped on the cell, i ran this function here
func showWatchView(selectedPath: Int) {
UIView.animate(withDuration: 0.3, animations: {
self.collectionViewBottomConstraint.constant = 0
})
clipsCollectionView.layoutIfNeeded()
}
However, when I tried this it moved the collection view to the top of the screen instead of the bottom of the screen, and it didn't even animate it, it just went up there.

Answer 1

The constant needs to be set to 0
class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {
#IBOutlet weak var collectionViewOutlet: UICollectionView!
#IBOutlet weak var bottomContraint: NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
collectionViewOutlet.delegate = self
collectionViewOutlet.dataSource = self
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
return cell
}
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
showWatchView(selectedPath: indexPath.item)
}
func showWatchView(selectedPath: Int) {
UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseOut, animations: {
self.bottomContraint.constant = 0
self.view.layoutIfNeeded()
}, completion: { (completed) in
// do something
})
}
}
Since you want the collectionView to be at the bottom and self.view.layoutIfNeeded() needs to be called inside the animation with a duration of your choosing, 0.3 is ok for starters.