iOS 页面滑动与标题切换颜色渐变的联动效果

• 设置UI界面
  • 将所有的子控制器添加到父控制器中
  • 添加UICollectionView，用于展示内容

1. // MARK:- 懒加载属性
   private lazy var collectionView : UICollectionView = {
   // 1.创建布局
   let layout = UICollectionViewFlowLayout()
   layout.itemSize = self.bounds.size
   layout.minimumLineSpacing = 0
   layout.minimumInteritemSpacing = 0
   layout.scrollDirection = .Horizontal
   // 2.创建collectionView
   let collectionView = UICollectionView(frame: self.bounds, collectionViewLayout: layout)
   collectionView.showsHorizontalScrollIndicator = false
   collectionView.pagingEnabled = true
   collectionView.bounces = false
   collectionView.scrollsToTop = false
   collectionView.dataSource = self
   collectionView.delegate = self
   collectionView.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: kContentCellID)
   return collectionView
   }()
   private func setupUI() {
   // 1.添加所有的控制器
   for childVc in childVcs {
   parentViewController?.addChildViewController(childVc)
   }
   // 2.添加collectionView
   addSubview(collectionView)
   }

    

• 在返回Cell的方法中，先将cell的contentView中的子控件都移除，防止循环引用
• 取出indexPath.item对应的控制器，将控制器的View添加到Cell的contentView中

  // MARK:- 遵守UICollectionView的数据源
  extension PageContentView : UICollectionViewDataSource {
  func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
  return childVcs.count
  }
  func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
  let cell = collectionView.dequeueReusableCellWithReuseIdentifier(kContentCellID, forIndexPath: indexPath)
  // 移除之前的
  for subview in cell.contentView.subviews {
  subview.removeFromSuperview()
  }
  // 取出控制器
  let childVc = childVcs[indexPath.item]
  childVc.view.frame = cell.contentView.bounds
  cell.contentView.addSubview(childVc.view)
  return cell
  }
  }

   

  PageTitleView点击改变PageContentView

• 通过代理将PageTitleView的事件传递出去

  /// 定义协议
  protocol PageTitleViewDelegate : class {
  func pageTitleView(pageTitleView : PageTitleView, didSelectedIndex index : Int)
  }
  @objc private func titleLabelClick(tapGes : UITapGestureRecognizer) {
  // 1.获取点击的下标志
  guard let view = tapGes.view else { return }
  let index = view.tag
  // 2.滚到正确的位置
  scrollToIndex(index)
  // 3.通知代理
  delegate?.pageTitleView(self, didSelectedIndex: index)
  }

   

  内部调整

  // 内容滚动
  private func scrollToIndex(index : Int) {
  // 1.获取最新的label和之前的label
  let newLabel = titleLabels[index]
  let oldLabel = titleLabels[currentIndex]
  // 2.设置label的颜色
  newLabel.textColor = kSelectTitleColor
  oldLabel.textColor = kNormalTitleColor
  // 3.scrollLine滚到正确的位置
  let scrollLineEndX = scrollLine.frame.width * CGFloat(index)
  UIView.animateWithDuration(0.15) {
  self.scrollLine.frame.origin.x = scrollLineEndX
  }
  // 4.记录index
  currentIndex = index
  }

   

• 在PageContentView中设置当前应该滚动的位置

1. // MARK:- 对外暴露方法
2. extension PageContentView {
3. func scrollToIndex(index : Int) {
4. let offset = CGPoint(x: CGFloat(index) * collectionView.bounds.width, y: 0)
5. collectionView.setContentOffset(offset, animated: false)
6. }
7. }

通过观察，我们发现：

                1> 原来位置的Title颜色会逐渐变暗

                2> 目标位置的Title颜色会逐渐变亮

                3> 变化程度是和滚动的多少相关

• 由此得出结论：
我们一共需要获取三个值
• 1> 起始位置下标值
• 2> 目标位置下标值
• 3> 当前滚动的进度 

        其实前2点可以由第3点计算而来，可以只需要将进度传递出去。

• 根据进度值处理标题颜色渐变及滑块逻辑

         。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
    }
}