单击选项卡栏时如何将表格视图发送到集合视图单元格的顶部？

Question

所以我有一个视图控制器，其集合视图包含 numberOfItemsInSection 中的两个集合视图单元格。每个单元格中都有一个表格视图。单击某个选项卡栏项目时，我试图转到表格视图的顶部。我的问题是我无法访问我的集合视图单元格中的标签栏，当我访问我的视图控制器中的标签栏并从视图控制器调用我的集合视图单元格中的一个函数时它不起作用（它说我我的表格视图中没有任何行）。

这是我在视图控制器中设置集合视图，并在视图控制器中调用 func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) 时尝试将集合视图单元格的表格视图发送到顶部。

class AllPostsVC: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, UITabBarControllerDelegate {
   var indexPath:IndexPath?

   override func viewDidLoad() {
        super.viewDidLoad()
        setupCollectionView()       
        self.tabBarController?.delegate = self
    }

    lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 0
        let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
        cv.dataSource = self
        cv.delegate = self
        return cv
    }()

    func setupCollectionView() {
        
        view.addSubview(collectionView)
        
        view.bringSubviewToFront(collectionView)
        
        collectionView.isPagingEnabled = true
        
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.heightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.heightAnchor).isActive = true
        collectionView.widthAnchor.constraint(equalTo: view.safeAreaLayoutGuide.widthAnchor).isActive = true
        
        collectionView.topAnchor.constraint(equalTo: self.menuBar.bottomAnchor).isActive = true
        
        collectionView.register(AllPostsCell.self, forCellWithReuseIdentifier: cellId)
        collectionView.register(AllPostsUnderReviewCell.self, forCellWithReuseIdentifier: postsUnderReviewcell)        
        
    }
    

    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        for cell in collectionView.visibleCells {
              indexPath = collectionView.indexPath(for: cell)
            print(indexPath)
        }
    }


    func scrollToMenuIndex(menuIndex: Int) {
        let indexPath = NSIndexPath(item: menuIndex, section: 0)
        collectionView.scrollToItem(at: indexPath as IndexPath, at: [], animated: true)
    }

    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {

        if tabBarIndex == 0 {
            if indexPath?.item == 0 {
                let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath!) as! AllPostsCell
                cell.sendToTop()
            }
        }
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 2
    }

     func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
     
        var albumsCell:UICollectionViewCell?
        
        if indexPath.item == 1 {
            let underReviewCell = collectionView.dequeueReusableCell(withReuseIdentifier: postsUnderReviewcell, for: indexPath) as! AllPostsUnderReviewCell
                underReviewCell.parent = self
                return underReviewCell
        }
        
         let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! AllPostsCell
         cell.parent = self
         return cell
  
        
    }

在我的收藏视图单元格中

class AllPostsCell: UICollectionViewCell, UITableViewDelegate, UITableViewDataSource {
    func sendToTop() {
        DispatchQueue.main.async {
            self.layoutIfNeeded()
            self.myTableView.layoutIfNeeded()
            let indexPath = NSIndexPath(row: 0, section: 0)
            self.myTableView.scrollToRow(at: indexPath as IndexPath, at: .top, animated: true)
        }
    }
}

当我这样做时，我得到了错误： Terminating app due to uncaught exception 'NSRangeException', reason: 'Attempted to scroll the table view to an out-of-bounds row (0) when there are only 0 rows in section 0. 即使我在表格视图中看到行。 虽然它确实再次调用了我的集合视图单元格的 init 方法。

那么当我点击某个标签栏项目时，将我的 tableview 发送到我的集合视图单元格中的顶部有什么好的解决方案？

Answer 1

解决方案：单击右侧标签栏索引后，我必须从视图控制器向集合视图单元发送通知。

在我的视图控制器中获取集合视图单元格的索引。

func scrollViewDidScroll(_ scrollView: UIScrollView) {
        menuBar.horizontalBarLeftAnchorConstraint?.constant = scrollView.contentOffset.x / 2
        let visibleRect = CGRect(origin: collectionView.contentOffset, size: collectionView.bounds.size)
            let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
            indexPath = collectionView.indexPathForItem(at: visiblePoint)
    }

单击某个选项卡栏项后，从视图控制器向某个集合视图单元发送通知。

func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {

        let tabBarIndex = tabBarController.selectedIndex

        if tabBarIndex == 0 {
            if indexPath?.item == 0 {
                NotificationCenter.default.post(name: Notification.Name("sendToTop"), object: nil)
            } else if indexPath?.item == 1 {
                NotificationCenter.default.post(name: Notification.Name("sendToTopUR"), object: nil)
                
            }
        }
    }

索引 0 处的集合视图单元格

override init(frame: CGRect) {
        super.init(frame: frame)
   NotificationCenter.default.addObserver(self, selector: #selector(sendToTop), name: NSNotification.Name(rawValue: "sendToTop"), object: nil)
}

@objc func sendToTop() {
        DispatchQueue.main.async {
            self.layoutIfNeeded()
            self.myTableView.layoutIfNeeded()
            let indexPath = NSIndexPath(row: 0, section: 0)
            self.myTableView.scrollToRow(at: indexPath as IndexPath, at: .top, animated: true)
        }
    }