ios - 约束动画不起作用

Question

我正在尝试在 2 个约束中设置优先级变化的动画，但我似乎无法让它发挥作用。我的动画代码是这样写的:

        UIView.animate(withDuration: 0.2, animations: {
        if self.cardHeaderBottomtoBodyTopConstraint.priority == UILayoutPriorityDefaultHigh {
            self.cardHeaderBottomtoBodyTopConstraint.priority = UILayoutPriorityDefaultLow
            self.cardHeaderBottomToBodyBottomConstraint.priority = UILayoutPriorityDefaultHigh
        } else {
            self.cardHeaderBottomtoBodyTopConstraint.priority = UILayoutPriorityDefaultHigh
            self.cardHeaderBottomToBodyBottomConstraint.priority = UILayoutPriorityDefaultLow
        }

        self.flightInformationBodyCard.layoutIfNeeded()
        self.flightInformationBodyCard.updateConstraints()
    }, completion: nil)

Answer 1

我所要做的就是将 layoutIfNeeded 方法更改为 superview，如下所示:

        if self.cardHeaderBottomtoBodyTopConstraint.priority == UILayoutPriorityDefaultHigh {
        self.cardHeaderBottomtoBodyTopConstraint.priority = UILayoutPriorityDefaultLow
        self.cardHeaderBottomToBodyBottomConstraint.priority = UILayoutPriorityDefaultHigh
    } else {
        self.cardHeaderBottomtoBodyTopConstraint.priority = UILayoutPriorityDefaultHigh
        self.cardHeaderBottomToBodyBottomConstraint.priority = UILayoutPriorityDefaultLow
    }

    //self.flightInformationBodyCard.updateConstraints()

    UIView.animate(withDuration: 0.2, animations: {

        self.flightInformationBodyCard.superview?.layoutIfNeeded()

    }, completion: nil)