Swift UICollectionViewController 与 UICollectionViewCell 内的参数

Question

I'm configuring my cell like this:

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId for: indexPath) as! MyCollectionViewCell
    cell.index = indices[indexPath.item]
    return cell
}

And then inside my cell, I have another UICollectionViewController that has some property, say - index

class MyCollectionViewCell: UICollectionViewCell {       
    var index: Int = 0 
    var myController = UINavigationController(rootViewController: anotherCollectionViewController(index: self.index ?? 0))

    override init(frame: CGRect) {
        super.init(frame: frame)
        // setting constraints, adding views etc
        addSubview(anotherCollectionViewController.view)
        ....
    }
}

The issue is when I initialize cells, they are created with default index thus anotherCollectionViewController has a default index as well. How do I make it 'wait' for my index?

Answer 1

Better give alternate name to one of them.

Answer 2

You can use didSet function to init inner view controller, didSet is called immediately after the new value is stored:

class MyCollectionViewCell: UICollectionViewCell {
    var index: Int? {
        didSet {
            if let index = index {
                myController = UINavigationController(rootViewController: anotherCollectionViewController(index: index))
            }
        }
    }

    var myController: UINavigationController? {
        didSet {
            // remove old view controller from hierarchy
            // oldValue?.removeFromParent()
            // setting constraints, adding views etc
        }

    }

    override init(frame: CGRect) {
        super.init(frame: frame)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func prepareForReuse() {
        index = nil
        myController = nil
        super.prepareForReuse()
    }
}