Error: UICollectionView must be initialized with a non-nil layout parameter

Question

我正在尝试根据 YouTube 教程创建一个类似 Facebook Messenger 的应用程序。我有一个主页，用户可以在其中单击 BarButton 打开聊天。主页工作正常，直到我单击 BarButton 打开聊天，它崩溃并显示以下错误消息 "UICollectionView must be initialized with a non-nil layout parameter"。我是 iOS 开发的新手，所以无法真正理解问题到底是什么，因为我已经有了 init 方法。由于我有不同的观点，我是否在 AppDelegate 中遗漏了一些东西，这令人困惑 :( 。非常感谢你的帮助。谢谢！

class ChatViewController: UICollectionViewController, UICollectionViewDelegateFlowLayout {

override func viewDidLoad() {
    super.viewDidLoad()

    navigationItem.title = "Chats"

    collectionView?.backgroundColor = UIColor.gray

            // Do any additional setup after loading the view.
}

override func viewWillAppear(_ animated: Bool)
{
    collectionView?.register(ChatCell.self, forCellWithReuseIdentifier: "cellID")
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 3
}

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellID", for: indexPath)

    return cell
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    return CGSize(width: view.frame.width, height: 100)
}

/*
// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
}
*/

}

class ChatCell: UICollectionViewCell
{

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

let profileImageView: UIImageView =
{
    let imageView = UIImageView()
    imageView.contentMode = .scaleAspectFill
    imageView.translatesAutoresizingMaskIntoConstraints = false
    return imageView
}()

func setupViews()
{
    addSubview(profileImageView)

    backgroundColor = UIColor.blue

    addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0" : profileImageView]))
    addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0" : profileImageView]))
}

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

}

Answer 1

可能当你展示你的 ChatViewController 时，你有类似的东西：

让 chatVC = ChatViewController()

但根据 Apple 文档：

class UICollectionViewController

When you initialize the controller, using the init(collectionViewLayout:) method, you specify the layout the collection view should have.

所以你需要：

 let chatVC = ChatViewController(collectionViewLayout: UICollectionViewFlowLayout())

Answer 2

您似乎跳过了使用 Interface Builder 的教程中的步骤。

问题是，在您的 ChatViewController 中，您的 "collectionView?" 与 Interface Builder 中相应的 UICollectionView（所谓的引用出口）之间缺少连接。

这是 iOS 开发中的一项非常基本的任务。请查看主题 "Create Outlets for UI Elements" 下的官方 Apple 文档： Connect UI to Code

Error: UICollectionView must be initialized with a non-nil layout parameter

Error: UICollectionView must be initialized with a non-nil layout parameter

ios

uicollectionview

swift

swift3