iOS 10: infinite loop of UICollectionView's layoutSubviews if one of its subview's adjustsFontSizeToFitWidth = true

** Note that this issue does NOT happen on ios 9 but on ios 10 only.

I have a collection view with cell called "MyCell". Each MyCell contains a MyView, and MyView contains a MyLabel. 2 seconds after the viewcontroller did load, I trigger a call "setNeedsLayout" to one of visibleCells of collectionView to refresh its MyLabel's content.

If my MyLabel's adjustsFontSizeToFitWidth is not set, it works ok. But if I assign adjustsFontSizeToFitWidth = true, app will hang up with an infinite number of calls to "layoutSubviews".

The sample code is as following (~120 lines). If I comment out line #18, it works ok but the font is not scaled as I expected. If I leave it as is, app will hang up and crash due to out-of-memory error.

Thanks for your help.

import UIKit
import SnapKit
 
class MyView: UIView {   
    var myText: String = "" {
        didSet {
            self.setNeedsLayout()
        }
    }
   
    let myLabel = UILabel()
   
    override init(frame: CGRect) {
        super.init(frame: frame)
       
        self.backgroundColor = UIColor.whiteColor()
       
        myLabel.adjustsFontSizeToFitWidth = true
        self.addSubview(myLabel)
       
        myLabel.snp_remakeConstraints { (make) in
            make.size.equalTo(CGSizeMake(200, 50))
            make.center.equalTo(self)
        }
    }
   
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
   
    override func layoutSubviews() {
        super.layoutSubviews()
       
        self.myLabel.text = self.myText
    }
}
 
class MyCell: UICollectionViewCell {
   
    let myView = MyView()
   
    override init(frame: CGRect) {
        super.init(frame: frame)
       
        self.backgroundColor = UIColor.darkGrayColor()
       
        self.addSubview(myView)
       
        myView.snp_remakeConstraints { (make) in
            make.center.equalTo(self)
            make.size.equalTo(CGSizeMake(210, 60))
        }
    }
   
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
   
    override func layoutSubviews() {
        super.layoutSubviews()
       
        self.myView.myText = "Hello!!!"
    }
}
 
class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate {
    lazy var myCollectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .Vertical
        layout.minimumInteritemSpacing = 1.0
        layout.minimumLineSpacing = 1.0
       
        let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
        collectionView.dataSource = self
        collectionView.delegate = self       
        collectionView.registerClass(MyCell.self, forCellWithReuseIdentifier: "MyCell")
        return collectionView
    }()
   
    let myButton = UIButton()
   
    override func viewDidLoad() {
        super.viewDidLoad()
       
        self.view.addSubview(myCollectionView)
       
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(2 * NSEC_PER_MSEC)), dispatch_get_main_queue(), {
            self.myCollectionView.visibleCells().last?.setNeedsLayout()
        })
    }
   
    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        return 1
    }
   
    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 2
    }
   
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("MyCell", forIndexPath: indexPath)
        return cell
    }
   
    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
        return CGSizeMake(self.view.bounds.width, self.view.bounds.height)
    }
   
    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -> CGFloat {
        return 0
    }
   
    func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAtIndex section: Int) -> CGFloat {
        return 0
    }
}