Xcode中集合视图的单元格未出现

Question

我正在开发一个应用程序并设置一个 UICollectionView。下面是 UICollectionView 所在视图控制器的代码：

import UIKit
import Firebase
import FirebaseFirestoreSwift
import FirebaseFirestore

class scrollCollectionViewController: UICollectionViewController{
    var tournaments = [String]()
    @IBOutlet weak var collectionview: UICollectionView!
    override func viewDidLoad() {
        fetchTourneys()
        super.viewDidLoad()
        
        // Uncomment the following line to preserve selection between presentations
        // self.clearsSelectionOnViewWillAppear = false

        // Register cell classes
        

        // Do any additional setup after loading the view.
    }
    
    func fetchTourneys() {
       let db = Firestore.firestore()
       db.collection("Tournaments").getDocuments() { (querySnapshot, err) in
               if let err = err {
                   print("Error getting documents: \(err)")
               } else {
                   for document in querySnapshot!.documents {
                       print("\(document.documentID) => \(document.data())")
                       self.tournaments.append(document.documentID)
                   }
               }
       }
    }
    /*
    // 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.
    }
    */

    // MARK: UICollectionViewDataSource

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
    // #warning Incomplete implementation, return the number of sections
       return self.tournaments.count
    }


    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    // #warning Incomplete implementation, return the number of items
       return 5
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
       let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "tourneyIdentifier", for: indexPath) as! ScrollCollectionViewCell
       cell.tournamentTitle.text = tournaments[indexPath.row]
       print(cell.tournamentTitle.text)
    // Configure the cell

       return cell
    }

    // MARK: UICollectionViewDelegate

    /*
    // Uncomment this method to specify if the specified item should be highlighted during tracking
    override func collectionView(_ collectionView: UICollectionView, shouldHighlightItemAt indexPath: IndexPath) -> Bool {
        return true
    }
    */

    /*
    // Uncomment this method to specify if the specified item should be selected
    override func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
        return true
    }
    */

    /*
    // Uncomment these methods to specify if an action menu should be displayed for the specified item, and react to actions performed on the item
    override func collectionView(_ collectionView: UICollectionView, shouldShowMenuForItemAt indexPath: IndexPath) -> Bool {
        return false
    }

    override func collectionView(_ collectionView: UICollectionView, canPerformAction action: Selector, forItemAt indexPath: IndexPath, withSender sender: Any?) -> Bool {
        return false
    }

    override func collectionView(_ collectionView: UICollectionView, performAction action: Selector, forItemAt indexPath: IndexPath, withSender sender: Any?) {
    
    }
    */
}

细胞只是没有最终出现。在包含一些打印语句后，我注意到 numberOfSections 的覆盖函数或集合视图似乎都没有运行。为什么这些没有运行，以及为什么单元格没有出现，可能是什么问题？

Answer 1

你需要在numberOfItemsInSection中返回self.tournaments.count

func fetchTourneys() {
    let db = Firestore.firestore()
    db.collection("Tournaments").getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            for document in querySnapshot!.documents {
                print("\(document.documentID) => \(document.data())")
                self.tournaments.append(document.documentID)
            }
            
                self.collectionview.reloadData()
            
        }
    }
}



override func numberOfSections(in collectionView: UICollectionView) -> Int {
    // #warning Incomplete implementation, return the number of sections
           return 1
       }


       override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    // #warning Incomplete implementation, return the number of items
           return self.tournaments.count
       }

Answer 2

请移动fetchTourneys() 在 super.viewDidLoad() 之后。此外，您需要确保正确设置单元格标识符并在您的 collectionView 中注册

private let reuseIdentifier = "tourneyIdentifier"

class scrollCollectionViewController: UICollectionViewController {
    var tournaments = [String]()

    @IBOutlet weak var collectionview: UICollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Register cell classes
        self.collectionview!.register(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
        fetchTourneys()
    }

然后，在创建单元格时，重新使用reuseIdentifier

.dequeueReusableCell(withReuseIdentifier: reuseIdentifier

此外，在您的 Firebase 函数中，确保在填充数据源后告诉 collectionView 进行更新

if let err = err {
    print("Error getting documents: \(err)")
} else {
    for document in querySnapshot!.documents {
        print("\(document.documentID) => \(document.data())")
        self.tournaments.append(document.documentID)
    }
    self.collectionview.reloadData()
}

你也说过

我没有注意到 numberOfSections 或 集合视图似乎正在运行

这表明您的 UICollectionView 不知道此代码是 viewController。确保您已在 XCode Inspector 中进行设置。一般来说，Classes 和 Structs 应该以大写字母开头，vars 是小写的

Answer 3

一旦fetchTourneys 完成，您必须在collectionview 上致电reloadData。

func fetchTourneys() {
    let db = Firestore.firestore()
    db.collection("Tournaments").getDocuments() { (querySnapshot, err) in
        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            for document in querySnapshot!.documents {
                print("\(document.documentID) => \(document.data())")
                self.tournaments.append(document.documentID)
            }
            self.collectionview.reloadData()
        }
    }
}

Answer 4

你需要在viewDidLoad中设置collectionview数据源并委托给self

将delegate = self 和dataSource = self 放入viewDidLoad

Answer 5

每个人的答案都指出了代码中的错误，从而将其移向了正确的方向。但它仍然没有显示细胞。我打印了每个单元格，并注意到有一个参数使它们全部隐藏。我不知道是什么原因造成的。但我添加了以下代码：

    cell.isHidden = false

效果很好！