UITableViewCell布局在单元被重用之前不会更新 [英] UITableViewCell layout not updating until cell is reused

问题描述

我有一个自动填充单元格大小的UITableView. UITableView设置非常简单:

I have a UITableView that I fill with autosizing cells. UITableView setup is fairly simple:

    tableView.estimatedRowHeight = 70
    tableView.rowHeight = UITableViewAutomaticDimension

与Apple完全相同，建议在这里进行以下操作: https ://developer.apple.com/library/content/documentation/UserExperience/Conceptual/AutolayoutPG/WorkingwithSelf-SizingTableViewCells.html

Exactly like Apple recommends here: https://developer.apple.com/library/content/documentation/UserExperience/Conceptual/AutolayoutPG/WorkingwithSelf-SizingTableViewCells.html

要启用自动调整大小的表格视图单元格，您必须将表格视图的 UITableViewAutomaticDimension的rowHeight属性.你还必须 将一个值分配给estimateRowHeight属性.两者都 设置这些属性后，系统将使用自动布局"来计算 行的实际高度.

To enable self-sizing table view cells, you must set the table view’s rowHeight property to UITableViewAutomaticDimension. You must also assign a value to the estimatedRowHeight property. As soon as both of these properties are set, the system uses Auto Layout to calculate the row’s actual height.

在配置单元格时，我还禁用/启用了一些约束以实现所需的外观.那就是事情变得有趣的地方.在重新使用单元之前，单元布局不会更新.字面上地.您可以调用layoutIfNeeded()，setNeedsLayout()，layoutSubviews()或任何其他方法，无法强制单元更新其布局.

When configuring a cell I also disable/enable some constraints to achieve the needed look. That’s where things get interesting. Cell layout is not updated until the cell is reused. Literally. You can call layoutIfNeeded(), setNeedsLayout(), layoutSubviews() or any other method there is, there is no way you will force the cell to update its layout.

所有其他方面的效果都很好:标签确实可以更改其文本，您可以隐藏/取消隐藏视图，但是布局会一直停留到重新使用单元格为止.

All other aspects work pretty good: labels do change their text, you hide/unhide the views, but layout is stuck until the cell is reused.

问题:是什么原因引起的，以及如何避免这种行为?

Question: what causes it and how to avoid this behavior?

推荐答案

我也遇到了您的问题.而不是删除

I had your problem too. Instead of remove

tableView.estimatedRowHeight = 70

我刚刚在返回单元格本身之前，在cellForRow方法的末尾添加了一个layoutIfNeeded:

I just added a layoutIfNeeded at the end of the cellForRow method, just before return the cell itself:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "identifier", for: indexPath) as? MyCustomCell
    ...
    cell?.layoutIfNeeded()
    return cell!
}

结果:第一次，每次重复使用后，单元布局始终是完美的.

Result: the cell layout is perfect always, the first time and every after reuse.

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