UICollectionView inside a UITableViewCell — dynami

Question

One of our application screens requires us to place a UICollectionView inside of a UITableViewCell. This UICollectionView will have a dynamic number of items, resulting in a height which must be calculated dynamically as well. However, I am running into problems trying to calculate the height of the embedded UICollectionView.

Our overarching UIViewController was created in Storyboards and does make use of auto layout. But, I don't know how to dynamically increase the height of the UITableViewCell based on the height of the UICollectionView.

Can anyone give some tips or advice on how to accomplish this?

Answer 1

Pablo Romeu's answer above (https://stackoverflow.com/a/33364092/2704206) helped me immensely with my issue. I had to do a few things differently, however, to get this working for my problem. First off, I didn't have to call layoutIfNeeded() as often. I only had to call it on the collectionView in the systemLayoutSizeFitting function.

Secondly, I had auto layout constraints on my collection view in the table view cell to give it some padding. So I had to subtract the leading and trailing margins from the targetSize.width when setting the collectionView.frame's width. I also had to add the top and bottom margins to the return value CGSize height.

To get these constraint constants, I had the option of either creating outlets to the constraints, hard-coding their constants, or looking them up by an identifier. I decided to go with the third option to make my custom table view cell class easily reusable. In the end, this was everything I needed to get it working:

class CollectionTableViewCell: UITableViewCell {

    // MARK: -
    // MARK: Properties
    @IBOutlet weak var collectionView: UICollectionView! {
        didSet {
            collectionViewLayout?.estimatedItemSize = CGSize(width: 1, height: 1)
            selectionStyle = .none
        }
    }

    var collectionViewLayout: UICollectionViewFlowLayout? {
        return collectionView.collectionViewLayout as? UICollectionViewFlowLayout
    }

    // MARK: -
    // MARK: UIView functions
    override func systemLayoutSizeFitting(_ targetSize: CGSize, withHorizontalFittingPriority horizontalFittingPriority: UILayoutPriority, verticalFittingPriority: UILayoutPriority) -> CGSize {
        collectionView.layoutIfNeeded()

        let topConstraintConstant = contentView.constraint(byIdentifier: "topAnchor")?.constant ?? 0
        let bottomConstraintConstant = contentView.constraint(byIdentifier: "bottomAnchor")?.constant ?? 0
        let trailingConstraintConstant = contentView.constraint(byIdentifier: "trailingAnchor")?.constant ?? 0
        let leadingConstraintConstant = contentView.constraint(byIdentifier: "leadingAnchor")?.constant ?? 0

        collectionView.frame = CGRect(x: 0, y: 0, width: targetSize.width - trailingConstraintConstant - leadingConstraintConstant, height: 1)

        let size = collectionView.collectionViewLayout.collectionViewContentSize
        let newSize = CGSize(width: size.width, height: size.height + topConstraintConstant + bottomConstraintConstant)
        return newSize
    }
}

As a helper function to retrieve a constraint by identifier, I add the following extension:

extension UIView {
    func constraint(byIdentifier identifier: String) -> NSLayoutConstraint? {
        return constraints.first(where: { $0.identifier == identifier })
    }
}

NOTE: You will need to set the identifier on these constraints in your storyboard, or wherever they are being created. Unless they have a 0 constant, then it doesn't matter. Also, as in Pablo's response, you will need to use UICollectionViewFlowLayout as the layout for your collection view. Finally, make sure you link the collectionView IBOutlet to your storyboard.

With the custom table view cell above, I can now subclass it in any other table view cell that needs a collection view and have it implement the UICollectionViewDelegateFlowLayout and UICollectionViewDataSource protocols. Hope this is helpful to someone else!

Answer 2

Pablo's solution did not work very well for me, I had strange visual effects (the collectionView not adjusting correctly).

What worked was to adjust the height constraint of the collectionView (as a NSLayoutConstraint) to the collectionView contentSize during layoutSubviews(). This is the method called when autolayout is applied to the cell.

// Constraint on the collectionView height in the storyboard. Priority set to 999.
@IBOutlet weak var collectionViewHeightConstraint: NSLayoutConstraint!


// Method called by autolayout to layout the subviews (including the collectionView).
// This is triggered with 'layoutIfNeeded()', or by the viewController
// (happens between 'viewWillLayoutSubviews()' and 'viewDidLayoutSubviews()'.
override func layoutSubviews() {

    collectionViewHeightConstraint.constant = collectionView.contentSize.height
    super.layoutSubviews()
}

// Call `layoutIfNeeded()` when you update your UI from the model to trigger 'layoutSubviews()'
private func updateUI() {
    layoutIfNeeded()
}

Answer 3

Easiest approach I've came up with, so far, Credits to @igor answer above,

In your tableviewcell class just insert this

override func layoutSubviews() {
    self.collectionViewOutlet.constant = self.postPoll.collectionViewLayout.collectionViewContentSize.height
}

and of course, change the collectionviewoutlet with your outlet in the cell's class

Answer 4

I was facing the same issue recently and I almost tried every solution in the answers, some of them worked and others didn't my main concern about @PabloRomeu approach is that if you have other contents in the cell (other than the collection view) you will have to calculate their heights and the heights of their constraints and return the result to get the auto layout right and I don't like to calculate things manually in my code. So here is the solution that worked fine for me without doing any manual calculations in my code.

in the cellForRow:atIndexPath of the table view I do the following:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    //do dequeue stuff
    //initialize the the collection view data source with the data
    cell.frame = CGRect.zero
    cell.layoutIfNeeded()
    return cell
}

I think what happens here is that I force the tableview cell to adjust its height after the collection view height has been calculated. (after providing the collectionView date to the data source)

Answer 5

I think, my way is much more simple, then proposed by @PabloRomeu.

Step 1. Create outlet from UICollectionView to UITableViewCell subclass, where UICollectionView is placed. Let, it's name will be collectionView

Step 2. Add in IB for UICollectionView height constraint and create outlet to UITableViewCell subclass too. Let, it's name will be collectionViewHeight.

Step 3. In tableView:cellForRowAtIndexPath: add code:

// deque a cell
cell.frame = tableView.bounds;
[cell layoutIfNeeded];
[cell.collectionView reloadData];
cell.collectionViewHeight.constant = cell.collectionView.collectionViewLayout.collectionViewContentSize.height;

Answer 6

Maybe my variant will be useful; i've been deciding this task during last two hours. I don't pretend it's 100% correct or optimal, but my skill's very small yet and i'd like to hear comments from experts. Thank you. One important note: this works for static table - it's specified by my current work. So, all I use is viewWillLayoutSubviews of tableView. And a little bit more.

private var iconsCellHeight: CGFloat = 500 

func updateTable(table: UITableView, withDuration duration: NSTimeInterval) {
    UIView.animateWithDuration(duration, animations: { () -> Void in
        table.beginUpdates()
        table.endUpdates()
    })
}

override func viewWillLayoutSubviews() {
    if let iconsCell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: 0, inSection: 1)) as? CategoryCardIconsCell {
        let collectionViewContentHeight = iconsCell.iconsCollectionView.contentSize.height
        if collectionViewContentHeight + 17 != iconsCellHeight {
            iconsCellHeight = collectionViewContentHeight + 17
            updateTable(tableView, withDuration: 0.2)
        }
    }
}

override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
    switch (indexPath.section, indexPath.row) {
        case ...
        case (1,0):
            return iconsCellHeight
        default:
            return tableView.rowHeight
    }
}

1. I know, that the collectionView is located in the first row of the second section;
2. Let the height of the row is 17 p. bigger, than its content height;
3. iconsCellHeight is a random number as the program starts (i know, that in the portrait form it has to be exactly 392, but it's not important). If the content of collectionView + 17 is not equal this number, so change its value. Next time in this situation the condition gives FALSE;
4. After all update the tableView. In my case its the combination of two operations (for nice updating of extending rows);
5. And of course, in the heightForRowAtIndexPath add one row to code.