我有一个滚动视图,当它向下滚动时,背景颜色会改变。
我知道我可以使用 UIView 动画来实现此自动化。但我想根据滚动的百分比设置颜色。
我想设置 0% 和 100% 颜色,并且当前颜色将被计算并设置为scrollViewDidScroll
0% 50% 100%
yellow green blue
EDIT
如何根据滚动位置计算新颜色?
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)
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