。当前进度值唯一确定了标题的状态，计算出需要发生颜色变化的两相邻标题索引
。注意：下标值需要防止越界问题，临界点的处理
实现代码
extension PageContentView : UICollectionViewDelegate {
func scrollViewWillBeginDragging(scrollView: UIScrollView) {
startOffsetX = scrollView.contentOffset.x
}
func scrollViewDidScroll(scrollView: UIScrollView) {
// 0.判断是否是点击事件
if isForbidScrollDelegate { return }
// 1.定义获取需要的数据
var progress : CGFloat = 0
let currentOffsetX = scrollView.contentOffset.x
let scrollViewW = scrollView.bounds.width
// 1.计算progress
progress = currentOffsetX / scrollViewW
// 3.将progress传递给titleView
delegate?.pageContentView(self, progress: progress)
}
}
根据滚动传入的值，调整PageTitleView
两种颜色必须使用RGB值设置（方便通过RGB实现渐变效果）
private let kNormalRGB : (CGFloat, CGFloat, CGFloat) = (85, 85, 85)
private let kSelectRGB : (CGFloat, CGFloat, CGFloat) = (255, 128, 0)
private let kDeltaRGB = (kSelectRGB.0 - kNormalRGB.0, kSelectRGB.1 - kNormalRGB.1, kSelectRGB.2 - kNormalRGB.2)
private let kNormalTitleColor = UIColor(red: 85/255.0, green: 85/255.0, blue: 85/255.0, alpha: 1.0)
private let kSelectTitleColor = UIColor(red: 255.0/255.0, green: 128/255.0, blue: 0/255.0, alpha: 1.0)
调整scrollLine及两个Label颜色渐变
// MARK:- 对外暴露方法
extension PageTitleView
func changeLabel(progress: CGFloat) {
// 开启弹簧效果时的过滤处理
var progress = progress > 0 ? progress : 0
progress = progress <= CGFloat(titleLabels.count - 1) ? progress : CGFloat(titleLabels.count - 1)
var leftLabelIndex = Int(floor(progress))
let ratio = progress - CGFloat(leftLabelIndex)
//获取leftLabel和rightLabel
let leftLabel = titleLabels[leftLabelIndex]
if leftLabelIndex >= 3{
leftLabelIndex = 3
}
print("leftLabelIndex = (leftLabelIndex)")
var rightIndex = leftLabelIndex + 1
if rightIndex >= 3{
rightIndex = 3
}
print("rightIndex = (rightIndex)")
let rightLabel = titleLabels[rightIndex]
//滑块的逻辑
let moveTotalX = leftLabel.frame.width
let moveX = moveTotalX * ratio
scrollLine.frame.origin.x = leftLabel.frame.origin.x + moveX
//3.Label颜色的渐变
// 3.1.取出变化的范围
let colorDelta = (kSelectedColor.0 - kNormalColor.0, kSelectedColor.1 - kNormalColor.1, kSelectedColor.2 - kNormalColor.2)
if leftLabelIndex != rightIndex {
// 3.2.变化leftLabel
leftLabel.textColor = UIColor(r: kSelectedColor.0 - colorDelta.0 * ratio, g: kSelectedColor.1 - colorDelta.1 * ratio, b: kSelectedColor.2 - colorDelta.2 * ratio)
// 3.2.变化rightLabel
rightLabel.textColor = UIColor(r: kNormalColor.0 + colorDelta.0 * ratio, g: kNormalColor.1 + colorDelta.1 * ratio, b: kNormalColor.2 + colorDelta.2 * ratio)
}
// 4.记录最新的index
currentIndex = leftLabelIndex
}
}
