CollectionView "Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value"

Question

我使用故事板制作了一个 collectionView，一切正常，collectionView 按预期从 firebase 获取数据。当我试图以语法方式制作相同的 collectionView 以便更好地控制布局时，我收到此错误：“致命错误：在隐式展开可选值时意外发现 nil”

self.collectionView.reloadData()

我不知道是什么原因导致这个错误

故事板

import UIKit
import FirebaseFirestore
import FirebaseAuth
import Kingfisher


class storyCollection: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {
    
    
    @IBOutlet weak var collectionView: UICollectionView!
    
    private var listener: ListenerRegistration?
    
    
    private var profiles = [Profile]() {
      didSet {
        DispatchQueue.main.async {
          self.collectionView.reloadData()
        }
      }
    }
      
    
    override func viewDidLoad() {
        super.viewDidLoad()
   
        collectionView.dataSource = self
        collectionView.delegate = self
        
        collectionView.register(UINib(nibName: "colCello", bundle: nil), 
        forCellWithReuseIdentifier: "colCello")
        
        
    }
    
    override func viewDidAppear(_ animated: Bool) {
      super.viewDidAppear(true)
       
        let user = Auth.auth().currentUser
     
        listener = Firestore.firestore().collection(DatabaseService.usersCollection).document(user!.uid).collection(DatabaseService.profilesCollection).addSnapshotListener({ [weak self] (snapshot, error) in
            
            
            if let error = error {
              DispatchQueue.main.async {
                self?.showAlert(title: "Try again later", message: "\(error.localizedDescription)")
              }
            } else if let snapshot = snapshot {
              
                let profile = snapshot.documents.map { Profile([=11=].data())}
            
                self?.profiles = profile
            }
          })
        }
        

    override func viewWillDisappear(_ animated: Bool) {
      super.viewWillDisappear(true)
        listener?.remove()
      }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return profiles.count

    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        if indexPath.row == 0 {
            let staticCell = collectionView.dequeueReusableCell(withReuseIdentifier: "colCello", for: indexPath) as! colCello


            staticCell.profileImageView.image = UIImage(systemName: "plus")!
            staticCell.backgroundColor = .systemYellow
            staticCell.profileNameLabel.text = "Add Profile"
            return staticCell
        } else {
        
          let defaultCell = collectionView.dequeueReusableCell(withReuseIdentifier: "colCello",   for: indexPath) as! colCello
       let profile = profiles[indexPath.row]
            defaultCell.configureCell(for: profile)
            defaultCell.backgroundColor = .systemTeal

       
       
       return defaultCell
    }
    }
}



class colCello: UICollectionViewCell {
    
    
    @IBOutlet weak var profileImageView: UIImageView!
    @IBOutlet weak var profileNameLabel: UILabel!
    
    public func configureCell(for profile: Profile) {
        profileImageView.kf.setImage(with: URL(string: profile.imageURL))
        profileNameLabel.text = profile.profileName
    
}
}

以编程方式

import UIKit
import FirebaseFirestore
import FirebaseAuth
import Kingfisher


class ProfilesViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    private var collectionView: UICollectionView!

    private var listener: ListenerRegistration?

    private var profiles = [Profile]()

    {
      didSet {
        DispatchQueue.main.async {
          self.collectionView.reloadData()
        }
      }
    }


         override func viewDidLoad() {
         super.viewDidLoad()

            let layout = UICollectionViewFlowLayout()
            layout.scrollDirection = .vertical
            let  collectionView = UICollectionView(frame: CGRect(x: 0, y: 0, width: 0, height: 0), collectionViewLayout: layout)
            collectionView.translatesAutoresizingMaskIntoConstraints = false
            collectionView.backgroundColor = .white
            collectionView.register(colCell6.self, forCellWithReuseIdentifier: "colCell6")
            collectionView.isPagingEnabled = false
            collectionView.frame = CGRect(x: 5, y: 0, width: view.frame.width-10, height: view.frame.height)

            collectionView.dataSource = self
            collectionView.delegate = self

            view.addSubview(collectionView)

    }

    override func viewDidAppear(_ animated: Bool) {
      super.viewDidAppear(true)

        let user = Auth.auth().currentUser

        listener = Firestore.firestore().collection(DatabaseService.usersCollection).document(user!.uid).collection(DatabaseService.profilesCollection).addSnapshotListener({ [weak self] (snapshot, error) in


            if let error = error {
              DispatchQueue.main.async {
                self?.showAlert(title: "Try again later", message: "\(error.localizedDescription)")
              }
            } else if let snapshot = snapshot {

                let profile = snapshot.documents.map { Profile([=12=].data())}

                self?.profiles = profile
            }
          })
        }


    override func viewWillDisappear(_ animated: Bool) {
      super.viewWillDisappear(true)
        listener?.remove()
      }


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


    }

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

        if indexPath.row == 0 {
            let staticCell = collectionView.dequeueReusableCell(withReuseIdentifier: "colCell6", for: indexPath) as! colCell6


            staticCell.profileImageView.image = UIImage(systemName: "plus")!
            staticCell.backgroundColor = .systemBackground
            staticCell.profileNameLabel.text = "Add Profile"
            return staticCell
        }

        let defaultCell = collectionView.dequeueReusableCell(withReuseIdentifier: "colCell6", for: indexPath) as! colCell6


        let profile = profiles[indexPath.row]
        defaultCell.backgroundColor = .systemTeal
        defaultCell.configureCell(for: profile)

        return defaultCell
    }


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

        return CGSize(width: (collectionView.frame.width-5)/2.0, height: 200)

        }
        func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
            return 5
        }
        func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
            return 0
        }


            }




class colCell6: UICollectionViewCell {




    static let identifier = "colCell6"
    var profileImageView: UIImageView = {
         let iv = UIImageView()
        iv.contentMode = .scaleAspectFill
        iv.clipsToBounds = true
        iv.backgroundColor = .yellow
        iv.layer.cornerRadius = 60

        return iv
    }()




    var profileNameLabel: UILabel = {
         let nl = UILabel()
        nl.contentMode = .scaleAspectFill
        nl.clipsToBounds = true
        nl.layer.cornerRadius = 10

        return nl
    }()


    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.addSubview(profileImageView)
        contentView.addSubview(profileNameLabel)

        contentView.clipsToBounds = true
        contentView.layer.cornerRadius = 10


        profileImageView.translatesAutoresizingMaskIntoConstraints = false
        profileImageView.leftAnchor.constraint(equalTo: contentView.leftAnchor, constant: 40).isActive = true
        profileImageView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 40).isActive = true
        profileImageView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: -40).isActive = true
        profileImageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -40).isActive = true
        profileImageView.contentMode = .scaleAspectFill

        profileNameLabel.translatesAutoresizingMaskIntoConstraints = false
        profileNameLabel.centerYAnchor.constraint(equalTo: self.contentView.centerYAnchor,constant: 80).isActive = true
        profileNameLabel.centerXAnchor.constraint(equalTo: self.contentView.centerXAnchor).isActive = true
    }

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

    public func configureCell(for profile: Profile) {
        profileImageView.kf.setImage(with: URL(string: profile.imageURL))
        profileNameLabel.text = profile.profileName





}

}

Answer 1

您永远不会为 private var collectionView 赋值，您声明了一个语言环境变量 collectionView，这是一个不同的对象。只需删除 let

替换

let collectionView = UICollectionView(frame: CGRect(x: 0, y: 0, width: 0, height: 0), collectionViewLayout: layout)

和

collectionView = UICollectionView(frame: CGRect(x: 0, y: 0, width: 0, height: 0), collectionViewLayout: layout)

Answer 2

此答案与@vadian 的答案相似。

使用

collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)

而不是

let collectionView = UICollectionView(frame: CGRect(x: 0, y: 0, width: 0, height: 0), collectionViewLayout: layout)

---

代替 CGRect(x: 0, y: 0, width: 0, height: 0)，您可以只使用 .zero

class ProfilesViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    
    private var collectionView: UICollectionView!
    
    private var listener: ListenerRegistration?
    
    private var profiles = [Profile]()  {
        didSet {
            DispatchQueue.main.async {
                self.collectionView.reloadData()
            }
        }
    }
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .vertical

        // Assign UICollectionView to the globle collectionView instead
        collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.backgroundColor = .white
        collectionView.register(colCell6.self, forCellWithReuseIdentifier: "colCell6")
        collectionView.isPagingEnabled = false
        collectionView.frame = CGRect(x: 5, y: 0, width: view.frame.width-10, height: view.frame.height)
        
        collectionView.dataSource = self
        collectionView.delegate = self
        
        view.addSubview(collectionView)
        
    }
    
    // Rest of your code
}