代码之家 › 专栏 › 技术社区 › Stefan

设置为活动时自动布局约束中断

nslayoutconstraint autolayout uiviewcontroller swift

Stefan · 技术社区 · 6 年前

我有一组AL约束来定位子vc,它有两个位置,展开和折叠。

我发现,当我添加折叠约束时,一个带有常量的顶部锚定到底部锚定约束,当vc第一次创建时,当我激活它时,似乎有额外的间距。似乎是因为当时没有实际的高度。

当我在viewDidLayoutSubviews中添加约束时,额外的间距消失了,约束行为正常。除了现在当我在动画中的约束之间切换时,当我切换到展开的约束和约束断开时,我不能停用折叠的约束。可能是因为viewDidLayoutSubviews在整个转换动画中被调用。

下面是vc设置的摘要。

var foregroundExpandedConstraint: NSLayoutConstraint!
var foregroundCollapsedConstraint: NSLayoutConstraint!

var foregroundViewController: UIViewController? {
    didSet {

        setupforegroundViewController(foregroundViewController: foregroundViewController!)
    }
}

func setupforegroundViewController(foregroundViewController: UIViewController) {

    addChildViewController(foregroundViewController)
    foregroundViewController.didMove(toParentViewController: self)

    guard let foregroundView = foregroundViewController.view else { return }
    foregroundView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(foregroundView)

    foregroundExpandedConstraint = foregroundView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 15)

    let height =  view.safeAreaLayoutGuide.layoutFrame.height - 50 - 15
    let cellHeight = ((height) / 6)        
    foregroundCollapsedConstraint = NSLayoutConstraint(item: foregroundView, attribute: .top, relatedBy: .equal, toItem: view.safeAreaLayoutGuide, attribute: .bottom, multiplier: 1, constant: (-cellHeight) * 2 - 50)

    let foregroundViewControllerViewConstraints = [
        foregroundView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        foregroundView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        foregroundView.heightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.heightAnchor, constant: -50 - 15),
        foregroundExpandedConstraint!
        ]


    NSLayoutConstraint.activate(foregroundViewControllerViewConstraints)
}

在这里,动画是使用UIViewPropertyAnimator来实现的。

func animateTransitionIfNeeded(state: ForegroundState, duration: TimeInterval) {

    let containerFrameAnimator = UIViewPropertyAnimator(duration: duration, dampingRatio: 1) {
        [unowned self] in

        switch state {
        case .expanded:
            self.foregroundCollapsedConstraint?.isActive = false
            self.foregroundExpandedConstraint?.isActive = true
            self.view.layoutIfNeeded()
        case .collapsed:
            self.foregroundExpandedConstraint?.isActive = false
            self.foregroundCollapsedConstraint?.isActive = true
            self.view.layoutIfNeeded()
        }
    }

    containerFrameAnimator.addCompletion {  [weak self] (position) in

        if position == .start {
            switch state {
            case .collapsed:
                self?.foregroundCollapsedConstraint?.isActive = false
                self?.foregroundExpandedConstraint?.isActive = true
                self?.foregroundIsExpanded = true
                self?.view.layoutIfNeeded()
            case .expanded:
                self?.foregroundExpandedConstraint?.isActive = false
                self?.foregroundCollapsedConstraint?.isActive = true
                self?.foregroundIsExpanded = false
                self?.view.layoutIfNeeded()
            }
        } else if position == .end {
            switch state {
            case .collapsed:
                self?.foregroundExpandedConstraint?.isActive = false
                self?.foregroundCollapsedConstraint?.isActive = true
                self?.foregroundIsExpanded = false
            case .expanded:
                self?.foregroundExpandedConstraint?.isActive = false
                self?.foregroundCollapsedConstraint?.isActive = true
                self?.foregroundIsExpanded = true
            }
        }
        self?.runningAnimations.removeAll()
    }

再次重申,当我使用以下代码时,将约束设置为vc添加到视图层次结构中时,它的布局不正确。检查约束,我看到它们在调用view-did布局子视图后发生了变化。除了折叠的约束外,每个约束都会相应地更改。

当我在view-did布局子视图中添加收拢的约束时,它的行为正常,但是我无法停用它,并且约束中断。

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    let height =  view.safeAreaLayoutGuide.layoutFrame.height - 50 - 15
    let cellHeight = ((height) / 6)

    if let v = foregroundViewController?.view {
        foregroundCollapsedConstraint = NSLayoutConstraint(item: v, attribute: .top, relatedBy: .equal, toItem: view.safeAreaLayoutGuide, attribute: .bottom, multiplier: 1, constant: (-cellHeight) * 2 - 50)
    }
}

我已经创建了一个回购协议来证明这个问题: https://github.com/louiss98/UIViewPropertyAnimator-Layout-Test

1 回复 | 直到 6 年前

DonMag 6 年前

您可以通过更改常量而不是创建新的约束来消除“断开”约束。

在你的 viewDidLayoutSubviews() 功能,

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    let height =  view.safeAreaLayoutGuide.layoutFrame.height - 50 - 15
    let cellHeight = ((height) / 6)

    foregroundCollapsedConstraint = NSLayoutConstraint(item: testViewController.view, attribute: .top, relatedBy: .equal, toItem: view.safeAreaLayoutGuide, attribute: .bottom, multiplier: 1, constant: (-cellHeight) * 2 - 50)
}

收件人:

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    let height =  view.safeAreaLayoutGuide.layoutFrame.height - 50 - 15
    let cellHeight = ((height) / 6)

    foregroundCollapsedConstraint.constant = (-cellHeight) * 2 - 50
}