如何更改屏幕上尚未显示的单元格的属性？

Question

我的应用包含时间表（UITableView）和日期栏（UICollectionView）。用户可以通过以下两种方法之一更改其选定日期：

1. 从DayBar中选择一天
2. 点击表格视图底部的“JumpToTomorrow”按钮。

现在的问题是，当我在第二天尚未滚动到屏幕的情况下单击它时，未选择当天的单元格（见下文）。

DayCollectionViewCell.isSelected （由于某种原因未被调用）

    override var isSelected: Bool {
    didSet {
        self.backgroundColor        = self.getBackgroundColor(selected: isSelected)
        self.layer.borderColor      = self.getBorderColor(selected: isSelected)
        self.number.attributedText  = NSAttributedString(string: number.text!, attributes: self.getTextAttributes(selected: isSelected))
    }
}

DayBarController功能

    override func viewDidLoad() {
    super.viewDidLoad()
    // To preserve selection between presentations
    self.clearsSelectionOnViewWillAppear = false
    setEdgeInsets()
    BroadcastManager.listen(to: PrepNotifications.JumpToTomorrowClicked, listenerId: "UpdateSelectedDay", react: updateSelectedDay)
}
    /// change the selected day and notify the app about the change
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    PrepGlobals.Calendar.SELECTED_DAY = indexPath.row
    BroadcastManager.broadcast(PrepNotifications.SelectedDayChanged)
    //scroll to center on selected day in case of clicked on today  
    if (PrepGlobals.Calendar.TODAY_INDEX == indexPath.row){
        self.collectionView?.scrollToItem(
            at: indexPath,
            at: .centeredHorizontally,
            animated: true
        )
    }
}

private func updateSelectedDay(_ userInfo: [AnyHashable: Any]? = nil) {
    PrepGlobals.Calendar.SELECTED_DAY += 1
    let selectedDayIndex = IndexPath(row: PrepGlobals.Calendar.SELECTED_DAY, section: 0)
    self.collectionView!.selectItem(at: selectedDayIndex, animated: true, scrollPosition: .right)
    BroadcastManager.broadcast(PrepNotifications.SelectedDayChanged)
}

Answer 1

您应修改collectionView(_:cellForItemAt:)以检查是否应选择单元格索引并更新其中的样式。

Answer 2

我编辑了我的答案。实际上你必须手动设置isSelected。

override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
      cell.isSelected = (indexPath.row == PrepGlobals.Calendar.SELECTED_DAY)
}

Answer 3

禁用预取已修复此问题。