ios - 即使调用了view.layoutIfNeeded()，Swift iOS -Constraint也不会进行动画处理

我有一个圆形的likeButton，它位于圆形的moreButton后面。 likeButton固定在moreButton的centerX和centerY上。当我按下moreButton时，我希望对moreButton上方200点的likeButton进行动画处理。

我使用NSLayoutConstraint来跟踪likeButton的centerY并对其进行更改。当我调用UIView.animate并在其闭包内部调用self.view.layoutIfNeeded()时，视图未更新。

@objc func moreButtonTapped(){

    likeButtonCenterY?.isActive = false
    likeButton.centerYAnchor.constraint(equalTo: self.moreButton.centerYAnchor, constant: -200)
    likeButtonCenterY?.isActive = true

    UIView.animate(withDuration: 0.3) {
        self.view.layoutIfNeeded()
    }
}

我要去哪里了？

let moreButton: UIButton = {
    let button = UIButton(type: .system)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.setImage(UIImage(named: "more"), for: .normal)
    button.tintColor = .red
    button.clipsToBounds = true
    button.addTarget(self, action: #selector(moreButtonTapped), for: .touchUpInside)
    return button
}()

let likeButton: UIButton = {
    let button = UIButton(type: .system)
    button.translatesAutoresizingMaskIntoConstraints = false
    button.setImage(UIImage(named: "like"), for: .normal)
    button.tintColor = .blue
    button.clipsToBounds = true
    return button
}()

var likeButtonCenterY: NSLayoutConstraint?

override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .white
    setAnchors()
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    moreButton.layer.cornerRadius = moreButton.frame.size.width / 2
    likeButton.layer.cornerRadius = likeButton.frame.size.width / 2
}

@objc func moreButtonTapped(){

    likeButtonCenterY?.isActive = false
    likeButton.centerYAnchor.constraint(equalTo: self.moreButton.centerYAnchor, constant: -200)
    likeButtonCenterY?.isActive = true

    UIView.animate(withDuration: 0.3) {
        self.view.layoutIfNeeded()
    }
}

func setAnchors(){
    view.addSubview(likeButton)
    view.addSubview(moreButton)

    moreButton.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    moreButton.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -200).isActive = true
    moreButton.widthAnchor.constraint(equalToConstant: 100).isActive = true
    moreButton.heightAnchor.constraint(equalToConstant: 100).isActive = true

    likeButtonCenterY = likeButton.centerYAnchor.constraint(equalTo: moreButton.centerYAnchor)
    likeButtonCenterY?.isActive = true

    likeButton.centerXAnchor.constraint(equalTo: moreButton.centerXAnchor).isActive = true
    likeButton.widthAnchor.constraint(equalToConstant: 100).isActive = true
    likeButton.heightAnchor.constraint(equalToConstant: 100).isActive = true
}

最佳答案

试试这个

@objc func moreButtonTapped(){

likeButtonCenterY?.isActive = false
likeButtonCenterY = likeButton.centerYAnchor.constraint(equalTo: self.moreButton.centerYAnchor, constant: -200)
likeButtonCenterY?.isActive = true

UIView.animate(withDuration: 0.3) {
    self.view.layoutIfNeeded()
}
}

您忘记写likeButtonCenterY =