Swift: change tableview height on scroll - ios

Question

I have a VC as shown in the image
It has a UICollectionView on top, and a UITableView at the bottom.
CollectionView has 1:3 of the screen and TableView has 2:3 of the screen(set using equalHeight constraint).
I want to change the height of the UICollectionView when the tableView is scrolled.
When the tableView is scrolled up,I want to change the multiplier of equalHeights constraint to like 1:5 and 4:5 of collectionView and tableView respectively.This will ensure that height of tableView increases and collectionView decreases
When the tableView is scrolled down, the multiplier of equalHeights constraint should reset to default.
I've tried adding swipe and pan gestures to tableView, but they are unrecognised.
How to achieve this functionality?
P.S: Would love to achieve this functionality by using a pan gesture, so that dragging up and down changes the heights progressively.
This is the view hierarchy
EDIT/UPDATE
This is the code that I'm using.
class MyConstant {
var height:CGFloat = 10
}
let myConstant = MyConstant()
MainScreenVC
override func viewWillAppear(_ animated: Bool) {
myConstant.height = self.view.frame.size.height
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if (self.lastContentOffset < scrollView.contentOffset.y) {
NotificationCenter.default.post(name: Notifications.decreaseHeightNotification.name, object: nil)
self.topViewConstraint.constant = -self.view.frame.height / 6
UIView.animate(withDuration: 0.3, animations: {
self.view.layoutIfNeeded()
})
} else if (self.lastContentOffset > scrollView.contentOffset.y) {
NotificationCenter.default.post(name: Notifications.increaseHeightNotification.name, object: nil)
self.topViewConstraint.constant = 0
UIView.animate(withDuration: 0.3, animations: {
self.view.layoutIfNeeded()
})
}
self.lastContentOffset = scrollView.contentOffset.y
}
Cell.Swift
override func awakeFromNib() {
super.awakeFromNib()
NotificationCenter.default.addObserver(self, selector: #selector(decreaseHeight), name: Notification.Name("decreaseHeightNotification"), object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(increaseHeight), name: Notification.Name("increaseHeightNotification"), object: nil)
self.contentView.translatesAutoresizingMaskIntoConstraints = false
heightConstraint.constant = (myConstant.height / 3) - 10
widthConstraint.constant = heightConstraint.constant * 1.5
}
#objc func decreaseHeight() {
heightConstraint.constant = (myConstant.height / 6) - 10
widthConstraint.constant = (heightConstraint.constant * 1.5)
self.layoutIfNeeded()
}
#objc func increaseHeight() {
heightConstraint.constant = (myConstant.height / 3) - 10
widthConstraint.constant = (heightConstraint.constant * 1.5)
self.layoutIfNeeded()
}
Now when I scroll both simultaneously, the screen freezes. Also is there a better way of resizing the collectionViewCell size?

Answer 1

I haven't tested it but you can do this. Use Autolayout in this view. it will work better with that.
Set the tableview constraint as Top, Left, Bottom, Right => 0, 0, 0, 0 with the main view and put collectionView under the tableview with constraint as Top,Left,Right, height => 0, 0, 0, x with the main view.
Note: Tableview is on top of the collectionView.
Connect your height constraint outlet of CollectionView and also define your defaultOffset variable
#IBOutlet weak var defaultHeightConstraint: NSLayoutConstraint
var defaultOffSet: CGPoint?
In viewDidLoad,
override func viewDidLoad() {
super.viewDidLoad()
tableView.contentInset = UIEdgeInsetsMake(collectionView.size.height, 0, 0, 0)
}
In viewDidAppear, write
override func viewDidAppear(_ animated: Bool) {
defaultOffSet = tableView.contentOffset
}
In ViewDidScroll
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let offset = tableView.contentOffset
if let startOffset = self.defaultOffSet {
if offset.y < startOffset.y {
// Scrolling down
// check if your collection view height is less than normal height, do your logic.
let deltaY = fabs((startOffset.y - offset.y))
defaultHeightConstraint.constant = defaultHeightConstraint.constant - deltaY
} else {
// Scrolling up
let deltaY = fabs((startOffset.y - offset.y))
defaultHeightConstraint.constant = defaultHeightConstraint.constant + deltaY
}
self.view.layoutIfNeeded()
}
}
Hope it helps.

Answer 2

Since UITableView is a subclass of UIScrollView, your table view's delegate can receive UIScrollViewDelegate methods.
You don't need to use PanGesture
First implement UITableviewDelegate and in that
var oldContentOffset = CGPoint.zero
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let contentOffset = scrollView.contentOffset.y - oldContentOffset.y
if (self.oldContentOffset < scrollView.contentOffset.y) {
// moved to top
} else if (self.oldContentOffset > scrollView.contentOffset.y) {
// moved to bottom
} else {
// didn't move
}
oldContentOffset = scrollView.contentOffset
}
Here you can write you logic to change constant value of your constraint
UPDATE/EDIT
Another thing is don't use multiplier for tabelview height.with collection view it is fine you can give height constraint with self.view in ratio of 1/3 . for tableview just give leading ,trailing top (UICollectionView) and bottom.
So when you change height constant of UICollectionView Tableview height automatically decrease and vice-versa for decrease.
You can not change the multiplier from the outlet as it is read only. so you have to constant value to self.view.frame.height / 3 will work for you
Hope it is helpful to you

Answer 3

For a much cleaner approach, why don't you use a UIScrollView as the container view and add the UICollectionView and UITableView inside it and give the collectionView a height constraint while disabling tableView's scroll till the height constraint of your collectionView becomes 0.
Here's the snippet:
Extend your VC with UIScrollViewDelegate and use:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if scrollView.contentOffset.y >= 0 && scrollView.contentOffset.y <= yourLimit {
heightConstraint.constant = collectionViewHeight - scrollView.contentOffset.y
tableView.isScrollEnabled = false
} else if scrollView.contentOffset.y > yourLimit {
heightConstraint.constant = collectionViewHeight
tableView.isScrollEnabled = true
}
}
Try this snippet after customizing small things in it. It should work mostly, if it doesn't there is another approach which I'd share once this doesn't work.

Answer 4

Why don't you just add Custom Table Cell with your collection view inside, and when indexPath.row == 0 , return your custom table cell.