应该配置自定义CollectionViewCell的ImageView为零

Question

I have a tableViewCell with a collectionView , collectionView's cells are custom ones, they contains just a imageView .

Here is my test project

Here are DataSource required methods from my CollectionView class :

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCell", for: indexPath) as! ImageCell

    let image = UIImage(named: listItems[indexPath.row])
    cell.testImageView.image = image

    return cell
}

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

When I try to set image for cell's imageView I get this error :

fatal error: unexpectedly found nil while unwrapping an Optional value

I have checked image , it isn't nil , but testImageView is, I get this error when I try to set image to collectionViewCell's testImageView. How can I fix it? EDIT1

Here is method called from tableViewController to fill collectionView's listItem

func load(listItem: [String]) {
    self.listItems = listItem
    reloadData()

}

Also if I remove code from collectionView cellForItemAt indexPath with this one all is working fine

let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCell", for: indexPath)
let imageView = UIImageView(image:UIImage(named: listItems[indexPath.row]))

cell.backgroundView = imageView

Answer 1

You have mistaken your two view controllers. Your IB outlet is connected to a cell in a different view controller. I mean you can have multiple views in different controllers connected to a same IBOutlet, but in your case the one that loads first is not connected, so that is why it crashes.

This is the cell your outlet was connected to.

This is that you are trying to load (but did not connect IBOutlet to image view):

Answer 2

Just in case you want to use code instead..

import UIKit


class ImageCell : UICollectionViewCell {

    private var imageView: UIImageView!
    private var descLabel: UILabel!

    public var image: UIImage? {
        get {
            return self.imageView.image
        }

        set {
            self.imageView.image = newValue
        }
    }

    public var imageDesc: String? {
        get {
            return self.descLabel.text
        }

        set {
            self.descLabel.text = newValue
        }
    }

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

        self.initControls()
        self.setTheme()
        self.doLayout()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        self.initControls()
        self.setTheme()
        self.doLayout()
    }

    override func awakeFromNib() {
        super.awakeFromNib()
    }

    func initControls() {
        self.imageView = UIImageView()
        self.descLabel = UILabel()
    }

    func setTheme() {
        self.imageView.contentMode = .scaleAspectFit

        self.descLabel.numberOfLines = 1
        self.descLabel.lineBreakMode = .byWordWrapping
        self.descLabel.textAlignment = .center
        self.descLabel.textColor = UIColor.black

        self.contentView.backgroundColor = UIColor.white
    }

    func doLayout() {
        self.contentView.addSubview(self.imageView)
        self.contentView.addSubview(self.descLabel)

        self.imageView.leftAnchor.constraint(equalTo: self.contentView.leftAnchor, constant: 5).isActive = true
        self.imageView.rightAnchor.constraint(equalTo: self.contentView.rightAnchor, constant: -5).isActive = true
        self.imageView.topAnchor.constraint(equalTo: self.contentView.topAnchor, constant: 0).isActive = true

        self.descLabel.leftAnchor.constraint(equalTo: self.contentView.leftAnchor, constant: 5).isActive = true
        self.descLabel.rightAnchor.constraint(equalTo: self.contentView.rightAnchor, constant: -5).isActive = true
        self.descLabel.topAnchor.constraint(equalTo: self.imageView.bottomAnchor, constant: 5).isActive = true
        self.descLabel.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor, constant: -5).isActive = true

        for view in self.contentView.subviews {
            view.translatesAutoresizingMaskIntoConstraints = false
        }
    }
}


class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    private var collectionView: UICollectionView!
    private var dataSource: Array<String>!

    override func viewDidLoad() {
        super.viewDidLoad()

        self.initDataSource()
        self.initControls()
        self.setTheme()
        self.registerClasses()
        self.doLayout()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    func initDataSource() {
        self.dataSource = ["Image1", "Image2", "Image3", "Image4", "Image5", "Image6"]
    }

    func initControls() {
        let layout = UICollectionViewFlowLayout()
        layout.itemSize = CGSize(width: 117, height: 125)
        layout.invalidateLayout()
        self.collectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
        self.collectionView.delegate = self
        self.collectionView.dataSource = self
    }

    func setTheme() {
        self.collectionView.backgroundColor = UIColor.clear

        self.edgesForExtendedLayout = UIRectEdge(rawValue: 0)
        self.view.backgroundColor = UIColor.blue
    }

    func registerClasses() {
        self.collectionView.register(ImageCell.self, forCellWithReuseIdentifier: "ImageCellIdentifier")
    }

    func doLayout() {
        self.view.addSubview(self.collectionView)

        self.collectionView.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
        self.collectionView.rightAnchor.constraint(equalTo: self.view.rightAnchor).isActive = true
        self.collectionView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
        self.collectionView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true

        for view in self.view.subviews {
            view.translatesAutoresizingMaskIntoConstraints = false
        }
    }

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.dataSource.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageCellIdentifier", for: indexPath) as! ImageCell

        let imageName = self.dataSource[indexPath.row]
        cell.image = UIImage(named: imageName)
        cell.imageDesc = imageName

        return cell
    }
}

http://imgur.com/o7O7Plw

Answer 3

maybe the "testImageView" outlet variable is not connected from the interface builder or there is no CollectionViewCell with reuseIdentifier "ImageCell". Check whether cell is nil or not using LLDB po command.