为什么在使用委托时我的 collectionView 为 nil？

Question

我有一个包含 2 个 CollectionView 的 TableView，每个 CollectionView 都在一个 TableViewCell 中。当我 select 第一个 CollectionView 中的一个项目时，我想更新第二个 CollectionView。我正在使用委托模式，但它不起作用，因为当我想使用 .reloadData 方法时我的第二个 CollectionView 似乎为 nil，但是为什么以及如何在 selecting 一个项目时实现更新第二个 CollectionView在第一个 CollectionView 中？

protocol TableViewCellDelegate {
func update()}

class TableViewCell: UITableViewCell, UICollectionViewDelegate, UICollectionViewDataSource {
var delegate: TableViewCellDelegate?

//...
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        self.delegate = ExistingInterestsCell() as? TableViewCellDelegate
        delegate?.update()}}


class ExistingInterestsCell: UITableViewCell, TableViewCellDelegate {
func update() {
    collectionView.reloadData()
}}

错误信息是：

Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value: file Suggest_Accounts_and_Docs/ExistingInterestsCell.swift, line 13

Answer 1

这一行

self.delegate = ExistingInterestsCell() as? TableViewCellDelegate

指的是一个 table 没有插座的电池，这就是它崩溃的原因，你需要访问一个真实的呈现的

编辑： 在两个单元格类中添加对 tableView 的引用，并使用 indexPath 和 table 获取需要单元格并更新它的集合

if let cell = table.cellForRow(at:Indexpath(row:0,section:0)) as? ExistingInterestsCell {
  // update model
  cell.collectionView.reloadData()
}

Answer 2

这是使用协议/委托模式的错误方式。您正在创建类彼此过于依赖。

更好的方法是让您的第一行告诉控制器它的一个集合视图单元格已被选中，然后允许控制器更新用于第二行的数据，然后重新加载该行。

因此，您的“第一行”单元格将包含：

class FirstRowTableViewCell: UITableViewCell, UICollectionViewDelegate, UICollectionViewDataSource {
    
    var didSelectClosure: ((Int) -> ())?
    
    var collectionView: UICollectionView!

    // cell setup, collection view setup, etc...
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        // tell the controller that a collection view cell was selected
        didSelectClosure?(indexPath.item)
    }

}

您的“第二行”单元格将包含：

class SecondRowTableViewCell: UITableViewCell, UICollectionViewDelegate, UICollectionViewDataSource {
    
    var collectionView: UICollectionView!
    
    var activeData: [String] = []
    
    // cell setup, collection view setup, etc...
    
}

在您的 table 视图控制器中，您将有一个变量，例如：

var dataType: Int = 0

你的 cellForRowAt 看起来像这样：

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if indexPath.row == 0 {
        let c = tableView.dequeueReusableCell(withIdentifier: "firstRowCell", for: indexPath) as! FirstRowTableViewCell

        // set the closure so the first row can tell us one of its
        //  collection view cells was selected
        c.didSelectClosure = { [weak self] i in
            guard let self = self else { return }
            // only reload if different cell was selected
            if i != self.dataType {
                self.dataType = i
                self.tableView.reloadRows(at: [IndexPath(row: 1, section: 0)], with: .automatic)
            }
        }
        return c
    }

    let c = tableView.dequeueReusableCell(withIdentifier: "secondRowCell", for: indexPath) as! SecondRowTableViewCell
    switch dataType {
    case 1:
        c.activeData = numberData
    case 2:
        c.activeData = wordData
    default:
        c.activeData = letterData
    }
    c.collectionView.reloadData()
    return c
}

这是一个完整的例子...

第一行Table单元格

class FirstRowTableViewCell: UITableViewCell, UICollectionViewDelegate, UICollectionViewDataSource {
    
    var didSelectClosure: ((Int) -> ())?
    
    var collectionView: UICollectionView!
    
    let myData: [String] = [
        "Letters", "Numbers", "Words",
    ]
    
    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    func commonInit() -> Void {
        
        let fl = UICollectionViewFlowLayout()
        fl.scrollDirection = .horizontal
        fl.minimumInteritemSpacing = 8
        fl.minimumLineSpacing = 8
        fl.estimatedItemSize = CGSize(width: 80.0, height: 60)
        
        collectionView = UICollectionView(frame: .zero, collectionViewLayout: fl)
        
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        
        contentView.addSubview(collectionView)
        
        let g = contentView.layoutMarginsGuide
        
        // to avoid auto-layout warnings
        let hConstraint = collectionView.heightAnchor.constraint(equalToConstant: 60.0)
        hConstraint.priority = .defaultHigh
        
        NSLayoutConstraint.activate([
            collectionView.topAnchor.constraint(equalTo: g.topAnchor),
            collectionView.leadingAnchor.constraint(equalTo: g.leadingAnchor),
            collectionView.trailingAnchor.constraint(equalTo: g.trailingAnchor),
            collectionView.bottomAnchor.constraint(equalTo: g.bottomAnchor),
            hConstraint,
        ])
        
        collectionView.register(SingleLabelCollectionViewCell.self, forCellWithReuseIdentifier: "cell")
        collectionView.dataSource = self
        collectionView.delegate = self
        
        collectionView.backgroundColor = .systemBlue
        
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return myData.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let c = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! SingleLabelCollectionViewCell
        c.theLabel.text = myData[indexPath.item]
        return c
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        // tell the controller that a collection view cell was selected
        didSelectClosure?(indexPath.item)
    }

}

第二行Table单元格

class SecondRowTableViewCell: UITableViewCell, UICollectionViewDelegate, UICollectionViewDataSource {
    
    var collectionView: UICollectionView!
    
    var activeData: [String] = []
    
    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    func commonInit() -> Void {
        
        let fl = UICollectionViewFlowLayout()
        fl.scrollDirection = .horizontal
        fl.minimumInteritemSpacing = 8
        fl.minimumLineSpacing = 8
        fl.estimatedItemSize = CGSize(width: 80.0, height: 60)
        
        collectionView = UICollectionView(frame: .zero, collectionViewLayout: fl)
        
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        
        contentView.addSubview(collectionView)
        
        let g = contentView.layoutMarginsGuide
        
        // to avoid auto-layout warnings
        let hConstraint = collectionView.heightAnchor.constraint(equalToConstant: 60.0)
        hConstraint.priority = .defaultHigh
        
        NSLayoutConstraint.activate([
            collectionView.topAnchor.constraint(equalTo: g.topAnchor),
            collectionView.leadingAnchor.constraint(equalTo: g.leadingAnchor),
            collectionView.trailingAnchor.constraint(equalTo: g.trailingAnchor),
            collectionView.bottomAnchor.constraint(equalTo: g.bottomAnchor),
            hConstraint,
        ])
        
        collectionView.register(SingleLabelCollectionViewCell.self, forCellWithReuseIdentifier: "cell")
        collectionView.dataSource = self
        collectionView.delegate = self
        
        collectionView.backgroundColor = .systemRed
        
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return activeData.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let c = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! SingleLabelCollectionViewCell
        c.theLabel.text = activeData[indexPath.item]
        return c
    }
    
}

Table 视图控制器

class MyTableViewController: UITableViewController {
    
    let numberData: [String] = [
        "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15",
    ]
    let letterData: [String] = [
        "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O",
    ]
    let wordData: [String] = [
        "First", "Second", "Third", "Fourth", "Fifth", "Sixth",
    ]

    var dataType: Int = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        tableView.register(FirstRowTableViewCell.self, forCellReuseIdentifier: "firstRowCell")
        tableView.register(SecondRowTableViewCell.self, forCellReuseIdentifier: "secondRowCell")
    }
    
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 2
    }
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        if indexPath.row == 0 {
            let c = tableView.dequeueReusableCell(withIdentifier: "firstRowCell", for: indexPath) as! FirstRowTableViewCell

            // set the closure so the first row can tell us one of its
            //  collection view cells was selected
            c.didSelectClosure = { [weak self] i in
                guard let self = self else { return }
                // only reload if different cell was selected
                if i != self.dataType {
                    self.dataType = i
                    self.tableView.reloadRows(at: [IndexPath(row: 1, section: 0)], with: .automatic)
                }
            }
            return c
        }

        let c = tableView.dequeueReusableCell(withIdentifier: "secondRowCell", for: indexPath) as! SecondRowTableViewCell
        switch dataType {
        case 1:
            c.activeData = numberData
        case 2:
            c.activeData = wordData
        default:
            c.activeData = letterData
        }
        c.collectionView.reloadData()
        return c
    }
    
}

集合视图单元格（两行均使用）

// simple single-label collection view cell
class SingleLabelCollectionViewCell: UICollectionViewCell {
    let theLabel = UILabel()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    func commonInit() -> Void {
        
        theLabel.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(theLabel)
        
        let g = contentView.layoutMarginsGuide
        
        NSLayoutConstraint.activate([
            theLabel.topAnchor.constraint(equalTo: g.topAnchor),
            theLabel.leadingAnchor.constraint(equalTo: g.leadingAnchor),
            theLabel.trailingAnchor.constraint(equalTo: g.trailingAnchor),
            theLabel.bottomAnchor.constraint(equalTo: g.bottomAnchor),
        ])
        
        theLabel.backgroundColor = .yellow
        
        contentView.layer.borderColor = UIColor.green.cgColor
        contentView.layer.borderWidth = 1
    }
    
}

结果：

点击“号码”，我们会看到：

点击“字词”，我们会看到：

为什么在使用委托时我的 collectionView 为 nil？

Why is my collectionView nil when using a delegate?

ios

uicollectionview

swift