UIView 上的 CollectionView 单元格实例（在委托之外）无法快速运行 5

Question

我有一个名为HorizontalMenuCollectionView的视图，我正在其上加载集合视图。 我只需将它与任何视图连接起来就可以使用它（来自身份检查员）。 一切都在完美地工作。 但是现在我想在开始加载此视图时设置第一个项目单元格的背景颜色。 但是单元格背景颜色没有改变。 我在这里缺少什么？ 非常感谢。

这是我尝试设置项目单元格背景颜色的功能

func selectinitialCell() {
    let selectedIndexPath = IndexPath(item: 0, section: 0)
    let cell = menuCollectionView.dequeueReusableCell(withReuseIdentifier: "HorizontalMenuCollectionViewCell", for: selectedIndexPath) as! HorizontalMenuCollectionViewCell
    cell.backgroundColor = UIColor.blue.withAlphaComponent(0.05)
    menuCollectionView.reloadData()
}

这是完整的HorizontalMenuCollectionView ：

import UIKit

protocol HorizontalMenuCollectionViewDelegate {
    func didSelectItemAtIndexPath(title: String)
}

class HorizontalMenuCollectionView: UIView {

    var horizontalMenuCollectionViewDelegate : HorizontalMenuCollectionViewDelegate!
    @IBOutlet weak var menuCollectionView: UICollectionView!
    var objectArray = [String?]()
    var isFirstTimeGettingCalled = true

    //This initializer will call from code
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.initialization()
    }

    //This initializer will call from XIB
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.initialization()
    }

    func initialization() {
        let view = Bundle.main.loadNibNamed("HorizontalMenuCollectionView", owner: self, options: nil)![0] as? UIView
        view?.frame = self.bounds
        self.autoresizingMask = [.flexibleHeight, .flexibleWidth]
        self.addSubview(view!)
        registerNib()
        selectinitialCell()
    }

    func selectinitialCell() {
        let selectedIndexPath = IndexPath(item: 0, section: 0)
        let cell = menuCollectionView.dequeueReusableCell(withReuseIdentifier: "HorizontalMenuCollectionViewCell", for: selectedIndexPath) as! HorizontalMenuCollectionViewCell
        cell.backgroundColor = UIColor.blue.withAlphaComponent(0.05)
        menuCollectionView.reloadData()
    }

    func registerNib() {
        let horizontalMenuCollectionViewCellNib = UINib(nibName: "HorizontalMenuCollectionViewCell", bundle: nil)
        menuCollectionView.register(horizontalMenuCollectionViewCellNib, forCellWithReuseIdentifier: "HorizontalMenuCollectionViewCell")
    }
}

extension HorizontalMenuCollectionView: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

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

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
    }

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

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

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let text = NSAttributedString(string: objectArray[indexPath.row]!)
        return CGSize(width: text.size().width + 80, height: self.bounds.height)
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HorizontalMenuCollectionViewCell", for: indexPath) as! HorizontalMenuCollectionViewCell
        cell.titleLabel.text = objectArray[indexPath.row]!

        let backgroundView = UIView()
        backgroundView.backgroundColor = UIColor.blue.withAlphaComponent(0.05)
        cell.selectedBackgroundView = backgroundView

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        menuCollectionView.scrollToItem(at: indexPath, at: .centeredHorizontally, animated: true)
        horizontalMenuCollectionViewDelegate.didSelectItemAtIndexPath(title: objectArray[indexPath.row]!)
    }
}

Ans 我访问它的视图控制器

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var horizontalMenuCollectionView: HorizontalMenuCollectionView!

    override func viewDidLoad() {
        super.viewDidLoad()
        horizontalMenuCollectionView.horizontalMenuCollectionViewDelegate = self
        horizontalMenuCollectionView.objectArray = ["A", "AA", "AAA", "AAAA", "AAAAA"]
    }
}

extension ViewController: HorizontalMenuCollectionViewDelegate {
    func didSelectItemAtIndexPath(title: String) {
        print("\(title)")
    }
}

完整的示例项目链接在这里

Answer 1

用下面的替换你的 func selectinitialCell() 。

func selectinitialCell() {
    menuCollectionView.performBatchUpdates({
        self.menuCollectionView.reloadData()
    }) { (finish) in
        if finish{
            let selectedIndexPath = IndexPath(row: 0, section: 0)
            self.menuCollectionView.selectItem(at: selectedIndexPath, animated: false, scrollPosition: .left)
        }
    }
}