ios - 如何将 View 动画化到 X 和 Y 的中心？

Question

我有一个 ImageView，它对 Helper Header View 有 centerX 和 centerY 约束，如下图所示

我想将该 Logo imageView 设置为位于屏幕中央的动画，如下图所示:

我已经尝试了一些代码，但它不起作用，老实说，我不确定下面的这段代码，这是我尝试的。也许你有更好的方法。这是我试过的

首先，我尝试为两个约束提供标识符:

然后我删除约束并创建一个新的约束，如下面的代码:

 UIView.animate(withDuration: 1.1, delay: 0.5, usingSpringWithDamping:  0.4, initialSpringVelocity: 0.0, animations: {

            // remove the initial constraint
            self.mainLogoCenterXConstraint.isActive = false
            self.mainLogoCenterYConstraint.isActive = false

            // create new constraint
            let newMainLogoCenterXConstraint = NSLayoutConstraint(
                item: self.mainLogoImageView,
                attribute: .centerX,
                relatedBy: .equal,
                toItem: self.view,
                attribute: .centerY,
                multiplier: 1.0,
                constant: 0)
            newMainLogoCenterXConstraint.identifier = "mainLogoCenterXConstraint"
            newMainLogoCenterXConstraint.isActive = true

            let newMainLogoCenterYConstraint = NSLayoutConstraint(
                item: self.mainLogoImageView,
                attribute: .centerY,
                relatedBy: .equal,
                toItem: self.view,
                attribute: .centerY,
                multiplier: 1.0,
                constant: 0)
            newMainLogoCenterYConstraint.identifier = "mainLogoCenterYConstraint"
            newMainLogoCenterYConstraint.isActive = true


            self.view.layoutIfNeeded()

        }, completion: nil)

但它崩溃并给出错误:

'NSInvalidLayoutConstraintException', reason: 'Constraint improperly relates anchors of incompatible types:

也许您有更好的方法来实现这一目标....

Answer 1

您在创建与 self.mainLogoImageView.centerX 和 self.view.centerY 相关的第一个约束时出错 - 将第二个约束更改为 self.view .centerX。您不能将 x 轴 anchor 绑定(bind)到 y 轴 anchor 。

此外，请确保正确设置动画，查看我关于如何使用自动布局执行此操作的回答 here .

在你的情况下:

// remove the initial constraint
self.mainLogoCenterXConstraint.isActive = false
self.mainLogoCenterYConstraint.isActive = false

// create new constraint
let newMainLogoCenterXConstraint = NSLayoutConstraint(
            item: self.mainLogoImageView,
            attribute: .centerX,
            relatedBy: .equal,
            toItem: self.view,
            attribute: .centerX,
            multiplier: 1.0,
            constant: 0)
newMainLogoCenterXConstraint.identifier = "mainLogoCenterXConstraint"
newMainLogoCenterXConstraint.isActive = true

let newMainLogoCenterYConstraint = NSLayoutConstraint(
            item: self.mainLogoImageView,
            attribute: .centerY,
            relatedBy: .equal,
            toItem: self.view,
            attribute: .centerY,
            multiplier: 1.0,
            constant: 0)
newMainLogoCenterYConstraint.identifier = "mainLogoCenterYConstraint"
newMainLogoCenterYConstraint.isActive = true

self.view.setNeedsLayout()

UIView.animate(withDuration: 1.1, delay: 0.5, usingSpringWithDamping:  0.4, initialSpringVelocity: 0.0, animations: {

    self.view.layoutIfNeeded()

}, completion: nil)