UIView 动画工作一次后就不起作用了

Question

我正在尝试为我的视图制作动画，但它只是第一次工作，即

isOpen = true

。它有效，但是当我再次调用我的函数时

isOpen = false

，没有任何变化。

父视图为

self

(

UIView

)。孩子是

label

（

UILabel

）。

private func expansionView(isOpen: Bool) {
    if isOpen {
        label.backgroundColor = .white
        NSLayoutConstraint.activate([
             label.centerYAnchor.constraint(equalTo: self.topAnchor),
             label.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 15),
         ])
        
        UIView.animate(withDuration: 1, animations: {
            self.layoutIfNeeded()
        }) { (_) in
            
        }
    } else {
        label.backgroundColor = .clear
        NSLayoutConstraint.activate([
             label.centerYAnchor.constraint(equalTo: self.centerYAnchor),
             label.leadingAnchor.constraint(equalTo: self.leadingAnchor , constant: 15),
         ])

        UIView.animate(withDuration: 1, animations: {
            self.layoutIfNeeded()
        }) { (_) in
            print("Animation Completed!!!")
        }
    }
}

Answer 1

您需要有两个约束才能使其中之一处于活动状态。 您还可以通过动画将标签的背景颜色更改为透明。您可以像下面这样简化您的功能。

// define both vertical constraints
var constraintToCenterYAnchor: NSLayoutConstraint!
var constraintToTopAnchor: NSLayoutConstraint!

// where you init your view..
init() {
    // init your constraints
    constraintToTopAnchor = label.centerYAnchor.constraint(equalTo: topAnchor)
    constraintToCenterYAnchor = label.centerYAnchor.constraint(equalTo: centerYAnchor)

    // set and activate other constraints once.
    label.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 15).isActive = true

    // update background color of the label
    label.backgroundColor = .clear
    label.layer.backgroundColor = UIColor.white.cgColor
}

// simplify your function
private func expansionView(_ isOpen: Bool) {
    constraintToTopAnchor.isActive = isOpen
    constraintToCenterYAnchor.isActive = !isOpen
    
    UIView.animate(withDuration: 1) {
        self.label.layer.opacity = isOpen ? 1.0 : 0.0
        self.layoutIfNeeded()
    }
}

Answer 2

您需要有两个约束来激活和停用......

lazy var centerXConstraint = label.centerYAnchor.constraint(equalTo: self.centerYAnchor)
lazy var topConstraint = label.leadingAnchor.constraint(equalTo: self.leadingAnchor , constant: 15)
    
    
    init() {
        label.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 15).isActive = true
    }
    private func expansionView(isOpen: Bool) {
        if isOpen {
            label.backgroundColor = .white
            
            centerXConstraint.isActive = false
            topConstraint.isActive = true
            
            UIView.animate(withDuration: 1, animations: {
                self.layoutIfNeeded()
            }) { (_) in
                
            }
        } else {
            label.backgroundColor = .clear
            
              centerXConstraint.isActive = true
              topConstraint.isActive = false
            UIView.animate(withDuration: 1, animations: {
                self.layoutIfNeeded()
            }) { (_) in
                print("Animation Completed!!!")
            }
        }
        
    }