如何将子视图定位在具有动态高度的子视图下方?

时间:2017-05-31 09:52:50

标签: ios swift uiview autolayout

我有以下UIView:

enter image description here

这是一个包含三个子视图的UIView。顶部的常规UILabel(Hello World),自定义UIViewController(CategoryList),其中包含带按钮(alpha,beta,...)的CollectionView和另一个带有标签(SALUT)的自定义UIViewController。

我以编程方式进行自动布局,并将SALUT(var sCtrl)置于CategoryList(var catList)下面

sCtrl.view.topAnchor.constraint(equalTo: catList.view.bottomAnchor).isActive = true

这导致上面的图片,其中SALUT没有像我希望的那样位于类别列表下方。我有点理解为什么因为当我设置约束时,按钮尚未在CollectionView中正确布局,因此未设置catList的底部锚点。

在CategoryList:UIVIewController中我有以下内容以获取集合视图以获得正确的高度。

override public func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    heightConstraint = collectionView.heightAnchor.constraint(equalToConstant: collectionView.collectionViewLayout.collectionViewContentSize.height)
    self.view.addConstraint(heightConstraint)
}

这样可行,但由于在SALUT上设置约束后调用viewDidLayoutSubviews(),因此SALUT位置错误。我怎样才能轻松搞定? (我想我可以为我的主视图制作一个控制器,并在子视图布局后检查,然后更新子视图位置,但这对我来说似乎过于复杂了。)

主视图的完整代码如下所示,您可以看到布局定位代码。如果需要,我也可以提供子视图代码,但我想不应该需要它,因为它们应该被视为黑盒...

class MyView: UIView {

    let label = UILabel()
    var sCtrl : SubController
    var catList : CategoryList

    var topConstraint = NSLayoutConstraint()

    override init(frame: CGRect) {
        sCtrl = SubController()
        catList = CategoryList()
        super.init(frame: frame)
        setup()
    }

    private func setup() {
        self.backgroundColor = UIColor.green

        label.translatesAutoresizingMaskIntoConstraints = false
        label.backgroundColor = UIColor.yellow
        label.text = "Hello world"
        label.textAlignment = .center
        self.addSubview(label)

        catList.view.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(catList.view)

        sCtrl.view.translatesAutoresizingMaskIntoConstraints = false
        self.addSubview(sCtrl.view)

        let margins = self.layoutMarginsGuide

        label.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: 0).isActive = true
        label.trailingAnchor.constraint(equalTo: margins.trailingAnchor, constant: 0).isActive = true
        label.topAnchor.constraint(equalTo: margins.topAnchor, constant: 0).isActive = true
        label.heightAnchor.constraint(equalToConstant: 100.0).isActive=true

        catList.view.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: 0).isActive = true
        catList.view.topAnchor.constraint(equalTo: label.bottomAnchor, constant: 1.0).isActive = true
        catList.view.widthAnchor.constraint(equalTo: margins.widthAnchor, multiplier: 1.0).isActive = true
        catList.view.trailingAnchor.constraint(equalTo: margins.trailingAnchor, constant:0).isActive = true

        sCtrl.view.topAnchor.constraint(equalTo: catList.view.bottomAnchor).isActive = true
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

let v = MyView(frame: CGRect(x: 0, y: 0, width: 400, height: 600))

1 个答案:

答案 0 :(得分:0)

好的,我发现了这个问题。我错过了将高度约束添加到CategoryList自己的视图中。添加它可以正常工作。

override public func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    heightConstraint = collectionView.heightAnchor.constraint(equalToConstant: collectionView.collectionViewLayout.collectionViewContentSize.height)
    self.view.addConstraint(heightConstraint)
    //THE MISSING LINE!!
    self.view.heightAnchor.constraint(equalTo: self.collectionView.heightAnchor, constant: 0).isActive = true
}