Creating a UICollectionView programmatically with AutoLayout

Question

I'm trying to create a UICollectionView programmatically with AutoLayout and I have some issues.

First Test:

In my first try I created a UICollectionView as a Lazy var and added it in the viewDidLoad like this:

lazy var collection: UICollectionView = {
        let cv = UICollectionView()
        cv.translatesAutoresizingMaskIntoConstraints = false
        cv.setCollectionViewLayout(self.flowLayout, animated: true)
        cv.dataSource = self
        cv.delegate = self
        cv.registerClass(MyViewCell.self, forCellWithReuseIdentifier: "cell")
        return cv
}()


override func viewDidLoad() {
        super.viewDidLoad()

        self.view.addSubview(self.collection)
}

This approuch took me to this error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'UICollectionView must be initialized with a non-nil layout parameter'

Second Test:

So I had to use the frame/collectionViewLayout initializer and my second try looked like this:

lazy var collection: UICollectionView = {
        let cv = UICollectionView(frame: UIScreen.mainScreen().bounds, collectionViewLayout: self.flowLayout)
        cv.translatesAutoresizingMaskIntoConstraints = false
        cv.setCollectionViewLayout(self.flowLayout, animated: true)
        cv.dataSource = self
        cv.delegate = self
        cv.registerClass(MenuViewCell.self, forCellWithReuseIdentifier: "cell")
        return cv
}()


override func viewDidLoad() {
        super.viewDidLoad()

        self.view.addSubview(self.collection)

        //Constraints was there...

}

With this approuch I got a blank screen, using debugger I found out that the datasource delegate methods was called (numberOfItemsInSection and numberOfSectionsInCollectionView), but no other delegate methods was called (sizeForItemAtIndexPath and cellForItemAtIndexPath)

So I decided to get rid of autoLayout and see the way things work.

Third Test:

 lazy var collection: UICollectionView = {
        let cv = UICollectionView(frame: UIScreen.mainScreen().bounds, collectionViewLayout: self.flowLayout)
      //  cv.translatesAutoresizingMaskIntoConstraints = false
        cv.setCollectionViewLayout(self.flowLayout, animated: true)
        cv.dataSource = self
        cv.delegate = self
        cv.registerClass(MenuViewCell.self, forCellWithReuseIdentifier: "cell")
        return cv
    }()


override func viewDidLoad() {
        super.viewDidLoad()

        self.view.addSubview(self.collection)

        //No more constraints here !!!

}

And everything worked fine.

So, my question is: Is there a way to use UICollectionView Programmatically with AutoLayout ?

SOLUTION

After a while, I found out that my problem was in the constraints. Then I came out with this solution:

 let slice = (UIScreen.mainScreen().bounds.height / CGFloat(3.0)) 

    lazy var flowLayout:UICollectionViewFlowLayout = {
        let f = UICollectionViewFlowLayout()
        f.scrollDirection = UICollectionViewScrollDirection.Horizontal
        return f
    }()


    lazy var collection: UICollectionView = {
        let cv = UICollectionView(frame: CGRectZero, collectionViewLayout: self.flowLayout)
        cv.translatesAutoresizingMaskIntoConstraints = false
        cv.setCollectionViewLayout(self.flowLayout, animated: true)
        cv.dataSource = self
        cv.delegate = self
        cv.registerClass(MenuViewCell.self, forCellWithReuseIdentifier: "cell")
        return cv
    }()


    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.addSubview(self.collection)

        let views = ["collection":self.collection]

        var constraints =  NSLayoutConstraint.constraintsWithVisualFormat("H:|-0-[collection]-0-|", options: NSLayoutFormatOptions.AlignAllTop, metrics: nil, views: views)
        self.view.addConstraints(constraints)

        constraints =  NSLayoutConstraint.constraintsWithVisualFormat("V:|-\(slice)-[collection]-\(slice)-|", options: NSLayoutFormatOptions.AlignAllCenterX, metrics: nil, views: views)
        self.view.addConstraints(constraints)
    }

Answer 1

After a while, I figure out that my problem was in the constraints. Then I came out with this solution:

 let slice = (UIScreen.mainScreen().bounds.height / CGFloat(3.0)) 

    lazy var flowLayout:UICollectionViewFlowLayout = {
        let f = UICollectionViewFlowLayout()
        f.scrollDirection = UICollectionViewScrollDirection.Horizontal
        return f
    }()


    lazy var collection: UICollectionView = {
        let cv = UICollectionView(frame: CGRectZero, collectionViewLayout: self.flowLayout)
        cv.translatesAutoresizingMaskIntoConstraints = false
        cv.setCollectionViewLayout(self.flowLayout, animated: true)
        cv.dataSource = self
        cv.delegate = self
        cv.registerClass(MenuViewCell.self, forCellWithReuseIdentifier: "cell")
        return cv
    }()


    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.addSubview(self.collection)

        let views = ["collection":self.collection]

        var constraints =  NSLayoutConstraint.constraintsWithVisualFormat("H:|-0-[collection]-0-|", options: NSLayoutFormatOptions.AlignAllTop, metrics: nil, views: views)
        self.view.addConstraints(constraints)

        let stringConstraint = "V:|-\(slice)-[collection]-\(slice)-|"

        print("stringConstraint: \(stringConstraint)")

        constraints =  NSLayoutConstraint.constraintsWithVisualFormat(stringConstraint, options: NSLayoutFormatOptions.AlignAllCenterX, metrics: nil, views: views)
        self.view.addConstraints(constraints)
    }