逐渐根据滚动更改背景颜色

我有一个滚动视图，当它向下滚动时，背景会改变颜色。

我知道我可以使用UIView动画来自动完成。 但我想根据滚动的百分比设置颜色。

我想设置0％和100％颜色，并计算当前颜色并在scrollViewDidScroll上scrollViewDidScroll

  0% 50% 100% yellow green blue 

编辑

如何根据滚动位置计算新颜色？

Answer 1

这是Swift 3的解决方案。

 // This function calculates a new color by blending the two colors. // A percent of 0.0 gives the "from" color // A percent of 1.0 gives the "to" color // Any other percent gives an appropriate color in between the two func blend(from: UIColor, to: UIColor, percent: Double) -> UIColor { var fR : CGFloat = 0.0 var fG : CGFloat = 0.0 var fB : CGFloat = 0.0 var tR : CGFloat = 0.0 var tG : CGFloat = 0.0 var tB : CGFloat = 0.0 from.getRed(&fR, green: &fG, blue: &fB, alpha: nil) to.getRed(&tR, green: &tG, blue: &tB, alpha: nil) let dR = tR - fR let dG = tG - fG let dB = tB - fB let rR = fR + dR * CGFloat(percent) let rG = fG + dG * CGFloat(percent) let rB = fB + dB * CGFloat(percent) return UIColor(red: rR, green: rG, blue: rB, alpha: 1.0) } // Pass in the scroll percentage to get the appropriate color func scrollColor(percent: Double) -> UIColor { var start : UIColor var end : UIColor var perc = percent if percent < 0.5 { // If the scroll percentage is 0.0..<0.5 blend between yellow and green start = UIColor.yellow end = UIColor.green } else { // If the scroll percentage is 0.5..1.0 blend between green and blue start = UIColor.green end = UIColor.blue perc -= 0.5 } return blend(from: start, to: end, percent: perc * 2.0) } // In your "scrollViewDidScroll" delegate, calculate the scroll // percentage as a value from 0.0 to 1.0 // Then call "scrollColor" let scrollPercentage = ... // your calculation let scrollColor = scrollColor(percent: scrollPercentage)