ios - 奇怪的行为 CGAffineTransform

Question

我尝试为 UILabel 设置动画:

let label: UILabel = UILabel()
var transform = CGAffineTransform.identity

UIView.animate(withDuration: 2, animations: {
    self.transform = self.transform.translatedBy(x: 0, y: -150)
    self.transform = self.transform.scaledBy(x: 2, y: 2)
    self.label.transform = self.transform
})

效果很好。我有一个按钮，并添加了一个选择器，这样当按下它时，标签会再次出现动画:

func performSearch() {
    UIView.animate(withDuration: 2, animations: {
        self.transform = self.transform.translatedBy(x: 0, y: -300)
        self.label.transform = self.transform
    })
}

但它实际上所做的是按原始状态缩小标签，将其向下移动到屏幕底部，然后进行动画处理，尽管我希望它做的只是向上移动。为什么？

Answer 1

变换可能有点令人困惑...因为您已经缩放变换，进一步的变换似乎是通过缩放“自动调整”的，但不是以一种真正直观或明显的方式。

这可能会帮助您走得更远:

// initial animation
UIView.animate(withDuration: 2, animations: {
    self.transform = self.transform.translatedBy(x: 0, y: -150)
    self.transform = self.transform.scaledBy(x: 2, y: 2)
    self.label.transform = self.transform
})

// "resuming" animation
func performSearch() {
    let distance: CGFloat = -300 / 2
    self.transform = self.transform.translatedBy(x: 0, y: distance)
    self.label.transform = self.transform

    UIView.animate(withDuration: 2, animations: {
        self.transform = self.transform.translatedBy(x: 0, y: distance)
        self.label.transform = self.transform
    })


}