Question

我知道这个问题已被多次询问过，但我似乎无法深究这个问题。

使用自动布局，我想基于其子视图自动设置容器UIView的高度。我已经看过使用sizeToFit和其他各种方法来总结我的子视图的高度，但是根据我所读到的，当使用自动布局时，我的容器高度的高度应该是自动的，因为子视图“内在的”内容大小。

以下是我正在经历的简化案例。我真的很感激任何指导！

概述：

创建容器UIView，固定在superview的左右两侧，没有明确的高度，将其centerY与其superview centerY对齐
创建300宽度乘以100高度的UIView，将其作为子视图添加到容器视图，将其centerX与容器视图的centerX对齐，将pin与容器视图的上边缘对齐
重复步骤＃2，除非此时将其顶部固定在＃2的下边缘
容器视图的预期高度为200，但其高度实际上仍为0（因此中心对齐关闭）

代码：

class ViewController: UIViewController {

    let redView = RedView()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(redView)
        view.setNeedsUpdateConstraints()
    }

}

class RedView: UIView {

    let greenView = GreenView()
    let blueView = BlueView()

    init() {
        super.init(frame: CGRect.zero)

        translatesAutoresizingMaskIntoConstraints = false
        backgroundColor = UIColor.red()

        addSubview(greenView)
        addSubview(blueView)
        setNeedsUpdateConstraints()
    }

    override func updateConstraints() {
        super.updateConstraints()

        NSLayoutConstraint(item: greenView, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1, constant: 0).isActive = true
        NSLayoutConstraint(item: blueView, attribute: .top, relatedBy: .equal, toItem: greenView, attribute: .bottom, multiplier: 1, constant: 0).isActive = true

        NSLayoutConstraint(item: self, attribute: .left, relatedBy: .equal, toItem: superview, attribute: .left, multiplier: 1, constant: 0).isActive = true
        NSLayoutConstraint(item: self, attribute: .right, relatedBy: .equal, toItem: superview, attribute: .right, multiplier: 1, constant: 0).isActive = true
        NSLayoutConstraint(item: self, attribute: .centerY, relatedBy: .equal, toItem: superview, attribute: .centerY, multiplier: 1, constant: 0).isActive = true
        NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 200).isActive = true
    }

}

class GreenView: UIView {

    init() {
        super.init(frame: CGRect.zero)

        translatesAutoresizingMaskIntoConstraints = false
        backgroundColor = UIColor.green()
    }

    override func updateConstraints() {
        super.updateConstraints()

        NSLayoutConstraint(item: self, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 300).isActive = true
        NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 100).isActive = true
        NSLayoutConstraint(item: self, attribute: .centerX, relatedBy: .equal, toItem: superview, attribute: .centerX, multiplier: 1, constant: 0).isActive = true
    }

}

class BlueView: UIView {

    init() {
        super.init(frame: CGRect.zero)

        translatesAutoresizingMaskIntoConstraints = false
        backgroundColor = UIColor.blue()
    }

    override func updateConstraints() {
        super.updateConstraints()

        NSLayoutConstraint(item: self, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 300).isActive = true
        NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 100).isActive = true
        NSLayoutConstraint(item: self, attribute: .centerX, relatedBy: .equal, toItem: superview, attribute: .centerX, multiplier: 1, constant: 0).isActive = true
    }

}

Answer 1

你需要将blueView的底部固定到redView的底部，只需将此行添加到redView的updateConstraints：

NSLayoutConstraint(item: blueView, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1, constant: 0).active = true

根据子视图

1 个答案: