ios - 使用下一个上层对象的 anchor

Question

目前我正在编写一个事件 - UIViewController，它具有三个 UITableViews 显示参与者、感兴趣的人和不能来的人。它们中的每一个都固定在标签下。 层次结构如下所示:

descriptionLabel | surePeopleLabel | surePeopleTV | maybePeopleLabel | maybePeopleTV | nopePeopleLabel | nopePeopleTV

现在我只想显示相关的 Labels 和 TableViews。例如，如果没有感兴趣的人，则不应显示关联的元素。

但这会导致一个问题:因为 nopePeopleLabel 的约束设置为从未添加的 maybePeopleTV 的 bottomAnchor，程序崩溃。

有谁知道将 anchor 设置到下一个现有上方对象的(平滑)方法？ 我添加了我的代码，尽管这不是必需的..

if let sureUsers = surePeopleTV.users, !sureUsers.isEmpty {
    scrollView.addSubview(surePeopleLabel)
    scrollView.addSubview(surePeopleTV)
    let sureTVHeight: CGFloat = CGFloat(sureUsers.count) * 60
    surePeopleLabel.anchor(top: descLabel.bottomAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 20, paddingLeft: padding, paddingBottom: 0, paddingRight: padding, width: 0, height: 0)
    surePeopleTV.anchor(top: surePeopleLabel.bottomAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 5, paddingLeft: 0, paddingBottom: 0, paddingRight: 0, width: 0, height: sureTVHeight)
}

if let maybeUsers = maybePeopleTV.users, !maybeUsers.isEmpty {
    scrollView.addSubview(maybePeopleLabel)
    scrollView.addSubview(maybePeopleTV)
    let maybeTVHeight: CGFloat = CGFloat(maybeUsers.count) * 60
    maybePeopleLabel.anchor(top: surePeopleTV.bottomAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 20, paddingLeft: padding, paddingBottom: 0, paddingRight: padding, width: 0, height: 0)
    maybePeopleTV.anchor(top: maybePeopleLabel.bottomAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 5, paddingLeft: 0, paddingBottom: 0, paddingRight: 0, width: 0, height: maybeTVHeight)
}

if let nopeUsers = nopePeopleTV.users, !nopeUsers.isEmpty {
    scrollView.addSubview(nopePeopleLabel)
    scrollView.addSubview(nopePeopleTV)
    let nopeTVHeight: CGFloat = CGFloat(nopeUsers.count) * 60
    nopePeopleLabel.anchor(top: maybePeopleLabel.bottomAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 20, paddingLeft: padding, paddingBottom: 0, paddingRight: padding, width: 0, height: 0)
    nopePeopleTV.anchor(top: nopePeopleLabel.bottomAnchor, left: view.leftAnchor, bottom: scrollView.bottomAnchor, right: view.rightAnchor, paddingTop: 5, paddingLeft: 0, paddingBottom: 0, paddingRight: 0, width: 0, height: nopeTVHeight)
}

Answer 1

var lowestObjAnchor: NSLayoutYAxisAnchor = descLabel.bottomAnchor

每次最低的 anchor 改变时覆盖这个属性，你会没事的。在代码中，这看起来像这样:

if let sureUsers = surePeopleTV.users, !sureUsers.isEmpty {
    scrollView.addSubview(surePeopleLabel)
    scrollView.addSubview(surePeopleTV)
    let sureTVHeight: CGFloat = CGFloat(sureUsers.count) * 60
    surePeopleLabel.anchor(top: lowestObjAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 20, paddingLeft: padding, paddingBottom: 0, paddingRight: padding, width: 0, height: 0)
    surePeopleTV.anchor(top: surePeopleLabel.bottomAnchor, left: view.leftAnchor, bottom: nil, right: view.rightAnchor, paddingTop: 5, paddingLeft: 0, paddingBottom: 0, paddingRight: 0, width: 0, height: sureTVHeight)

    lowestObjAnchor = surePeopleTV.bottomAnchor
}