UICollectionViewController Error in Swift 3.0: mus

问题:

I'm new to iOS development. I've been learning Swift, and today, I tried using UICollectionViewController.

My code is as follows:

 class ViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout {
    var colView: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
        layout.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10)
        layout.itemSize = CGSize(width: 90, height: 120)

        colView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
        colView.dataSource = self
        colView.delegate = self
        colView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
        colView.backgroundColor = UIColor.white
        self.view.addSubview(colView)
    }

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 14
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath as IndexPath)
        cell.backgroundColor = UIColor.orange
        return cell
    }


}

However, when I try to run it, I get the following error:

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

I have looked up previous posts discussing this issue, but I couldn't find anything that fixed my code.

How should I fix this?

回答1:

Thank you! I incorporated your suggestions. Below is the code that works:

class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
let cellId = "CellId"
var colView: UICollectionView!

override func viewDidLoad() {
    super.viewDidLoad()

    let layout = UICollectionViewFlowLayout()
    layout.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10)
    layout.itemSize = CGSize(width: 111, height: 111)

    colView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
    colView.delegate   = self
    colView.dataSource = self
    colView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
    colView.backgroundColor = UIColor.white

    self.view.addSubview(colView)
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 21
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath as IndexPath)
    cell.backgroundColor = UIColor.orange
    return cell
}

}

Again, thank you guys very much. Have an awesome day :D

回答2:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    let cellSize = CGSize(width: 90, height: 120)
    //
    return CGSizeMake(cellSize)
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {

    return UIEdgeInsetsMake(top: 20, left: 10, bottom: 10, right: 10)
}

回答3:

Just change the order like below one :

let layout = UICollectionViewFlowLayout()
layout.sectionInset = UIEdgeInsets(top: 20, left: 10, bottom: 10, right: 10)
layout.itemSize = CGSize(width: 90, height: 120)
colView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
self.view.addSubview(colView)
colView.delegate   = self
colView.dataSource = self
colView.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: "Cell")
colView.backgroundColor = UIColor.white

回答4:

You can set your code like this:

class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    let cellId = "Cell"

    lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        // ... layout parameters
        let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
        cv.backgroundColor = .white
        cv.delegate = self
        cv.dataSource = self
        return cv
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(collectionView)
        // ... add your auto layout constraints to the collection view
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellId)
    }

    // Delegate and Data Source Methods...

}