UITableView 动态单元格高度仅在滚动后才正确 [英] UITableView dynamic cell heights only correct after some scrolling

问题描述

我有一个带有自定义 UITableViewCell 的 UITableView 使用自动布局在故事板中定义.单元格有几个多行 UILabels.

I have a UITableView with a custom UITableViewCell defined in a storyboard using auto layout. The cell has several multiline UILabels.

UITableView 似乎可以正确计算单元格高度，但是对于前几个单元格，高度没有在标签之间正确划分.滚动一点后，一切都按预期工作(即使是最初不正确的单元格).

The UITableView appears to properly calculate cell heights, but for the first few cells that height isn't properly divided between the labels. After scrolling a bit, everything works as expected (even the cells that were initially incorrect).

- (void)viewDidLoad {
    [super viewDidLoad]
    // ...
    self.tableView.rowHeight = UITableViewAutomaticDimension;
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    TableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"TestCell"];
    // ...
    // Set label.text for variable length string.
    return cell;
}

是否有什么我可能遗漏的地方，导致自动布局在前几次无法正常工作?

Is there anything that I might be missing, that is causing auto layout not to be able to do its job the first few times?

我创建了一个示例项目来演示这种行为.

I've created a sample project which demonstrates this behaviour.

推荐答案

我不知道这是否有明确记录，但在返回单元格之前添加 [cell layoutIfNeeded] 可以解决您的问题.

I don't know this is clearly documented or not, but adding [cell layoutIfNeeded] before returning cell solves your problem.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    TableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"TestCell"];
    NSUInteger n1 = firstLabelWordCount[indexPath.row];
    NSUInteger n2 = secondLabelWordCount[indexPath.row];
    [cell setNumberOfWordsForFirstLabel:n1 secondLabel:n2];

    [cell layoutIfNeeded]; // <- added

    return cell;
}

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