Swift - 向下滚动向上滚动时，tableView单元格中的ImageView消失

Question

我有一个带自定义单元格的tableView 。 每个单元格中都有一个pictureView ，但根据用户是否发布图片，可能无法显示。 但是现在当我向下滚动然后在这个tableView滚动时， pictureViews消失了。 我应该做些什么改变？ 谢谢！

我使用Swift 4和Xcode 10.1。

// CUSTOM CELL

protocol ItemCellDelegate: NSObjectProtocol {
    func photoButton(cell: ItemCell)
    func adjustTextButton(cell: ItemCell)
    func repostButton(cell: ItemCell)
    func commentButton(cell: ItemCell)
    func actionButton(cell: ItemCell)
    func pictureView(cell: ItemCell)
}

func updateCell(with item: Item) {
            ......

    if (item.getImgUrl().count != 0) { // Has picture
        print ("show pictureView getImgUrl: " + item.getImgUrl())
        self.pictureView.isHidden = false
        let imageUrl = URL(string: item.getImgUrl())
        self.pictureView.sd_setImage(with: imageUrl, completed: nil)
    } else { // Has no pictures
        print ("NO show pictureView getImgUrl: " + item.getImgUrl())
        self.pictureView.isHidden = true
        self.pictureViewHeight.constant = 0
    }

    ......
}

//查看控制器

override func viewDidLoad() {

    super.viewDidLoad()

    navigationController?.navigationBar.titleTextAttributes = [NSAttributedString.Key.foregroundColor:UIColor(red:0.30, green:0.30, blue:0.30, alpha:1.0)]

    self.navigationController?.navigationBar.tintColor = UIColor(red:0.30, green:0.30, blue:0.30, alpha:1.0)

    self.navigationController?.navigationBar.shadowImage = UIImage()


    tableView.estimatedRowHeight = 250
    tableView.rowHeight = UITableView.automaticDimension

    DispatchQueue.main.async() {
        self.refresh(sender: self)
        self.tableView.reloadData()
    }

    if #available(iOS 11.0, *) {
        self.navigationController?.navigationBar.prefersLargeTitles = true
    }

    if ((profileId == iApp.sharedInstance.getId() && pageId == Constants.ITEMS_PROFILE_PAGE) || pageId == Constants.ITEMS_FEED_PAGE || pageId == Constants.ITEMS_STREAM_PAGE) {

        let newItemButton = UIBarButtonItem(barButtonSystemItem: .add , target: self, action: #selector(newItem))
        self.navigationItem.rightBarButtonItem  = newItemButton

    }

    // add tableview delegate

    tableView.delegate = self
    tableView.dataSource = self

    self.tableView.tableFooterView = UIView()

    self.refreshControl.addTarget(self, action: #selector(refresh), for: UIControl.Event.valueChanged)
    self.tableView.addSubview(refreshControl)
    self.tableView.alwaysBounceVertical = true

    // prepare for loading data

    self.showLoadingScreen()

    // start loading data

    self.loadData()

}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "ItemCell", for: indexPath) as! ItemCell

    cell.delegate = self

    cell.updateCell(with: items[indexPath.row])

    cell.showRepostButton.isUserInteractionEnabled = true

    return cell
}

Answer 1

你应该为约束设置一个正常数，因为单元格已经出列，如果你得到任何没有url的人，那么它的常量= 0所以它看起来是隐藏的

if (item.getImgUrl().count != 0) { // Has picture
    print ("show pictureView getImgUrl: " + item.getImgUrl())
    self.pictureView.isHidden = false
    self.pictureViewHeight.constant = 50           << here some value
    let imageUrl = URL(string: item.getImgUrl())
    self.pictureView.sd_setImage(with: imageUrl, completed: nil)
} else { // Has no pictures
    print ("NO show pictureView getImgUrl: " + item.getImgUrl())
    self.pictureView.isHidden = true
    self.pictureViewHeight.constant = 0
}

也是func updateCell(with item: Item) { call

self.layoutIfNeeded()