UICollectionView未呈现

Question

此代码启动了UICollectionView并分配了数据源。应该渲染单元格但是单元格没有渲染。 在这种情况下，数据源被提取出来。

import UIKit
class ViewController: UIViewController {

private let cellReuseIdentifier = "collectionCell"

    override func viewDidLoad() {
        super.viewDidLoad()
        let flowLayout = UICollectionViewFlowLayout()
        flowLayout.scrollDirection = .horizontal

        let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: flowLayout)
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellReuseIdentifier)

        let dataSource = DateSource()

        collectionView.dataSource = dataSource
        collectionView.backgroundColor = UIColor.cyan

        self.view.addSubview(collectionView)
    }
}

class DateSource:NSObject, UICollectionViewDataSource {
    let leftAndRightPaddings: CGFloat = 80.0
    let numberOfItemsPerRow: CGFloat = 7.0
    let screenSize: CGRect = UIScreen.main.bounds
    private let cellReuseIdentifier = "collectionCell"
    var items = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
    {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellReuseIdentifier, for: indexPath)
        cell.backgroundColor = UIColor.green
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize
    {
        let width = (screenSize.width-leftAndRightPaddings)/numberOfItemsPerRow
        return CGSize(width: width, height: width)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets
    {
        return UIEdgeInsets(top: 20, left: 8, bottom: 5, right: 8)
    }
}

但是，当数据源在ViewController中合并时，此代码呈现单元格

import UIKit
class ViewController: UIViewController, UICollectionViewDataSource {

private let cellReuseIdentifier = "collectionCell"
let leftAndRightPaddings: CGFloat = 80.0
let numberOfItemsPerRow: CGFloat = 7.0
let screenSize: CGRect = UIScreen.main.bounds
var items = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]

    override func viewDidLoad() {
        super.viewDidLoad()
        let flowLayout = UICollectionViewFlowLayout()
        flowLayout.scrollDirection = .horizontal

        let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: flowLayout)
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellReuseIdentifier)

        let dataSource = self

        collectionView.dataSource = dataSource
        collectionView.backgroundColor = UIColor.cyan

        self.view.addSubview(collectionView)
    }

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

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
    {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellReuseIdentifier, for: indexPath)
        cell.backgroundColor = UIColor.green
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize
    {
        let width = (screenSize.width-leftAndRightPaddings)/numberOfItemsPerRow
        return CGSize(width: width, height: width)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets
    {
        return UIEdgeInsets(top: 20, left: 8, bottom: 5, right: 8)
    }
}

我在这里有点迷失，有些东西要在DataSource中实例化，但是错过了吗？

Answer 1

在第一个代码段中，您已在viewDidLoad()中实例化数据源，

let dataSource = DateSource()

这会限制数据源对象在该方法范围内的生命周期。您需要将您的数据源声明为View Controller的成员;

import UIKit

class ViewController: UIViewController {

    let dataSource = DateSource()
    private let cellReuseIdentifier = "collectionCell"

    override func viewDidLoad() {
        super.viewDidLoad()
        let flowLayout = UICollectionViewFlowLayout()
        flowLayout.scrollDirection = .horizontal

        let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: flowLayout)
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: cellReuseIdentifier)

        collectionView.dataSource = dataSource
        collectionView.backgroundColor = UIColor.cyan

        self.view.addSubview(collectionView)
    }
...
..
}

第二个片段有效，因为数据源是self，它的范围将比collectionView的范围更长。