ios - 在加载时选择 Collection View 单元格 - 自定义 UICollectionView 类

Question

我有一个自定义 Collection View (tabBarCollectionView)，它应该在选择第一个单元格时加载，如下面的代码所示。然而，这是行不通的。我知道这一点，因为选择单元格时应该是不同的颜色，但事实并非如此。

override init(frame: CGRect) {
    super.init(frame: frame)

    tabBarCollectionView.register(TabBarCell.self, forCellWithReuseIdentifier: cellIdentifier)

    addSubview(tabBarCollectionView)
    tabBarCollectionView.translatesAutoresizingMaskIntoConstraints = false
    addConstraintsWithFormat("H:|[v0]|", views: tabBarCollectionView)
    addConstraintsWithFormat("V:|[v0]|", views: tabBarCollectionView)

    tabBarCollectionView.selectItem(at: IndexPath(item: 0, section: 0), animated: false, scrollPosition: [])
}

自定义 UIView 类的完整代码插入如下:

import Foundation
import UIKit

class TabBar: UIView, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {

let cellIdentifier = "Cell"
let imageNames = ["homeIcon", "exploreIcon", "addIcon", "inboxIcon", "profileIcon"]

lazy var tabBarCollectionView: UICollectionView = {

    // All collection view implementations in here

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

    collectionView.dataSource = self
    collectionView.delegate = self

    collectionView.backgroundColor = UIColor.clear

    return collectionView
}()

override init(frame: CGRect) {
    super.init(frame: frame)

    tabBarCollectionView.register(TabBarCell.self, forCellWithReuseIdentifier: cellIdentifier)

    addSubview(tabBarCollectionView)
    tabBarCollectionView.translatesAutoresizingMaskIntoConstraints = false
    addConstraintsWithFormat("H:|[v0]|", views: tabBarCollectionView)
    addConstraintsWithFormat("V:|[v0]|", views: tabBarCollectionView)

    self.tabBarCollectionView.allowsSelection = true
    self.tabBarCollectionView.selectItem(at: IndexPath(item: 0, section: 0), animated: false, scrollPosition: [])
}

override func layoutSubviews() {
    super.layoutSubviews()

    tabBarCollectionView.allowsSelection = true
    tabBarCollectionView.selectItem(at: IndexPath(item: 0, section: 0), animated: false, scrollPosition: [])
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 5
}

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

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! TabBarCell

    cell.backgroundColor = UIColor.clear
    cell.tabBarImageView.image = UIImage(named: imageNames[indexPath.item])?.withRenderingMode(.alwaysTemplate)
    cell.tabBarImageView.tintColor = UIColor.pinpointGrey

    return cell
}

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

    return CGSize(width: frame.width / 5, height: frame.height)
}

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

    return 0
}

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



}

class TabBarCell: UICollectionViewCell {

let tabBarImageView: UIImageView = {

    let imageView = UIImageView()
    imageView.image = UIImage(named: "homeIcon")?.withRenderingMode(.alwaysTemplate)
    imageView.tintColor = UIColor.pinpointGrey
    return imageView
}()

override init(frame: CGRect) {
    super.init(frame: frame)

    setupViews()
}

func setupViews() {

    backgroundColor = UIColor.clear

    addSubview(tabBarImageView)
    addConstraintsWithFormat("H:[v0(42)]", views: tabBarImageView)
    addConstraintsWithFormat("V:[v0(42)]", views: tabBarImageView)

    addConstraint(NSLayoutConstraint(item: tabBarImageView, attribute: .centerX, relatedBy: .equal, toItem: self, attribute: .centerX, multiplier: 1, constant: 0))
    addConstraint(NSLayoutConstraint(item: tabBarImageView, attribute: .centerY, relatedBy: .equal, toItem: self, attribute: .centerY, multiplier: 1, constant: 0))
}

override var isHighlighted: Bool {

    didSet {
        if tabBarImageView.isHighlighted == true {
            self.tabBarImageView.tintColor = UIColor.pinpointBlue
        } else {
            self.tabBarImageView.tintColor = UIColor.pinpointGrey
        }
    }
}

override var isSelected: Bool {

    didSet {
        tabBarImageView.tintColor = isSelected ? UIColor.pinpointBlue : UIColor.pinpointGrey
    }
}

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

Answer 1

你的数据源集在哪里？您是否单独加载它，然后执行 reloadData()？

如果是，那么您应该选择该单元格，而不是在 viewDidLoad 方法期间选择，因为在加载期间， Collection View 可能尚未填充。

您还可以添加到 viewWillAppear/viewDidAppear 方法，因为在填充 Collection View 后会调用该方法