ios - 通过 layoutIfNeeded() 动画特定的约束变化

Question

我已经以编程方式构建了 View ，然后为它们设置了动画。有一个 View 动画链，最后一个是要设置动画的按钮。

当我通过调用 layoutIfNeeded() 更改约束(这些约束独立于其他约束并且没有其他 View 与它相关)为按钮设置动画时，一切都工作正常，所有 View 都会更改并转到它们在动画中的初始位置。

我什至尝试了很多其他方法，例如更改 alpha 值等或使其消失。但每一次，它都会改变整个观点。

现在，我无法找出确切的原因。下面是它的代码。

是否可以通过 layoutIfNeeded() 或任何其他方式来更改特定约束来处理此功能？

import UIKit

var nextButton: UIButton!
var nextButtonHeightConstraint: NSLayoutConstraint?
var nextButtonWidthConstraint: NSLayoutConstraint?

override func viewDidLoad() {
    super.viewDidLoad()
    addNextButton()
}

// ..... function trigerred here.
@IBAction func triggerChange() {
    performCaptionAnimation()
}

func addNextButton() {
    nextButton = UIButton()
    nextButton.translatesAutoresizingMaskIntoConstraints = false
    nextButton.clipsToBounds = true
    nextButton.setTitle("Next", for: .normal)
    nextButton.backgroundColor = .white
    nextButton.isUserInteractionEnabled = true
    nextButton.titleLabel!.font = AvernirNext(weight: .Bold, size: 16)
    nextButton.setTitleColor(.darkGray, for: .normal)
    nextButton.roundAllCorners(withRadius: ActionButtonConstraint.height.anchor/2)
    nextButton.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(nextButtonPressed)))
    view.addSubview(nextButton)

    nextButtonHeightConstraint = nextButton.heightAnchor.constraint(equalToConstant: ActionButtonConstraint.height.anchor)
    nextButtonWidthConstraint = nextButton.widthAnchor.constraint(equalToConstant: ActionButtonConstraint.width.anchor)

    NSLayoutConstraint.activate([
        nextButton.rightAnchor.constraint(equalTo: view.rightAnchor, constant: ActionButtonConstraint.right.anchor),
        nextButton.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: ActionButtonConstraint.bottom.anchor),
        nextButtonHeightConstraint!, nextButtonWidthConstraint!
        ])
}

func performCaptionAnimation() {
    UIView.animate(withDuration: 0.4, delay: 0.0, options: [.curveEaseInOut], animations: {
        self.bannerTwoItemContainer.alpha = 1
        self.bannerTwoItemContainer.frame.origin.x -= (self.bannerTwoItemContainer.frame.width/2 + 10)
    }) { (done) in
        if done {
            UIView.animate(withDuration: 0.4, delay: 0.0, options: [.curveEaseInOut], animations: {
                self.bannerOneItemContainer.alpha = 1
                self.bannerOneItemContainer.frame.origin.x += self.bannerOneItemContainer.frame.width/2 + 10
            }) { (alldone) in
                if alldone {
                    // All changes here ......................
                    self.changeNextButtonContents()
                }
            }
        }
    }
}

// ------ This animation has issues and brings all the animation to it's initial point
func changeNextButtonContents() {
    self.nextButtonHeightConstraint?.constant = 40
    self.nextButtonWidthConstraint?.constant = 110
    UIView.animate(withDuration: 0.4, delay: 0.0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: [.curveEaseIn], animations: {
        self.nextButton.setTitleColor(.white, for: .normal)
        self.nextButton.setTitle("Try Now", for: .normal)
        self.nextButton.titleLabel?.font = AvernirNext(weight: .Bold, size: 18)
        self.nextButton.backgroundColor = blueColor
        self.nextButton.roundAllCorners(withRadius: 20)
        self.view.layoutIfNeeded()
    }, completion: nil)
}

Answer 1

问题是您的第一个动画会更改其 View 的 frame，如 self.bannerTwoItemContainer.frame.origin.x 中所示。但是您不能更改由约束 定位的事物的框架。如果这样做，那么一旦布局发生，约束就会重新生效。这正是你正在做的，也正是发生的事情。你说 layoutIfNeeded 并且你从未改变的约束被遵守。

重写您的第一个动画以更改 View 的约束，而不是框架，一切都会好起来的。