最近在仿寫 Instagram，它的 Timeline 控制器中， tableView滾動過程中navigationItem.titleView會相應(yīng)縮放，效果如下：

ScrollingScaleNavTitleView.gif

錯誤做法：

一開始我是在scrollViewDidScroll(_:)方法中用transform直接對navigationItem.titleView 進行縮放:

override func scrollViewDidScroll(scrollView: UIScrollView) {
  let factor = offsetY / 20
          if factor < 1 && factor > 0 {
              navigationItem.titleView?.transform =   CGAffineTransformMakeScale(1 - factor, 1 - factor)
              rightItemIconView!.transform = CGAffineTransformMakeScale(1 - factor, 1 - factor)
              navigationItem.titleView!.alpha = 1 - factor
              navigationItem.rightBarButtonItem?.customView?.alpha = 1 - factor
          } else if factor <= 0 {
            navigationItem.titleView?.transform = CGAffineTransformIdentity
            navigationItem.titleView!.alpha = 1
            rightItemIconView!.transform = CGAffineTransformIdentity
            navigationItem.rightBarButtonItem?.customView?.alpha = 1

        } else {
            navigationItem.titleView?.transform = CGAffineTransformIdentity
            navigationItem.titleView!.alpha = 0
            rightItemIconView!.transform = CGAffineTransformIdentity
            navigationItem.rightBarButtonItem?.customView?.alpha = 0
        }

        // 下面用到的 tableViewOriginHeight 是 NavBar 的 frame 還沒發(fā)生變化之前 tableView 的高度
        if offsetY >= 0 && offsetY <= UIConstant.UI_NAV_BAR_HEIGHT {
            navigationController?.navigationBar.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT - offsetY
            tableView.frame.origin.y = UIConstant.UI_NAV_BAR_HEIGHT + UIConstant.UI_STATUSBAR_HEIGHT - offsetY
            tableView.frame.size.height = tableViewOriginHeight + offsetY
        } else if offsetY > UIConstant.UI_NAV_BAR_HEIGHT {
            navigationController?.navigationBar.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT - UIConstant.UI_NAV_BAR_HEIGHT
            tableView.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT
            tableView.frame.size.height = tableViewOriginHeight + UIConstant.UI_NAV_BAR_HEIGHT + UIConstant.UI_STATUSBAR_HEIGHT
        } else {
            navigationController?.navigationBar.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT
            tableView.frame.origin.y = UIConstant.UI_NAV_BAR_HEIGHT + UIConstant.UI_STATUSBAR_HEIGHT
            tableView.frame.size.height = tableViewOriginHeight
        }

}

得到的結(jié)果是：

titleView 在縮放之后，沒有回復(fù)到原來的尺寸，樓主到現(xiàn)在還布吉島什么原因，有看到這里的大神請指點下，萬分感激

NavTitleViewScaleWrong.gif

解決辦法

• 把你要縮放的scaleView，用一個普通的UIView裝著，作為一個 container，然后把這個 container 設(shè)置為 navigationItem.titleView

func setupTitleView() {
        let titleView = UIView(frame: CGRectMake(0, 0, 100, 40))
        titleImageView = UIImageView(image: FLIconKit.imageOfNavTitleBgImg(size: titleView.frame.size))
        titleImageView!.clipsToBounds = true
        titleImageView!.frame = titleView.bounds
        titleView.addSubview(titleImageView!)
        titleView.backgroundColor = UIColor.blackColor()
        navigationItem.titleView = titleView
    }

• 在scrollViewDidScroll(_:)方法中用transform對scaleView 進行縮放:

override func scrollViewDidScroll(scrollView: UIScrollView) {
        let offsetY = scrollView.contentOffset.y
        let factor = offsetY / 20
        if factor < 1 && factor > 0 {
            titleImageView!.transform = CGAffineTransformMakeScale(1 - factor, 1 - factor)
            rightItemIconView!.transform = CGAffineTransformMakeScale(1 - factor, 1 - factor)
            navigationItem.titleView!.alpha = 1 - factor
            navigationItem.rightBarButtonItem?.customView?.alpha = 1 - factor
        } else if factor <= 0 {
            titleImageView!.transform = CGAffineTransformIdentity
            navigationItem.titleView!.alpha = 1
            rightItemIconView!.transform = CGAffineTransformIdentity
            navigationItem.rightBarButtonItem?.customView?.alpha = 1

        } else {
            titleImageView!.transform = CGAffineTransformIdentity
            navigationItem.titleView!.alpha = 0
            rightItemIconView!.transform = CGAffineTransformIdentity
            navigationItem.rightBarButtonItem?.customView?.alpha = 0
        }
        // 下面用到的 tableViewOriginHeight 是 NavBar 的 frame 還沒發(fā)生變化之前 tableView 的高度
        if offsetY >= 0 && offsetY <= UIConstant.UI_NAV_BAR_HEIGHT {
            navigationController?.navigationBar.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT - offsetY
            tableView.frame.origin.y = UIConstant.UI_NAV_BAR_HEIGHT + UIConstant.UI_STATUSBAR_HEIGHT - offsetY
            tableView.frame.size.height = tableViewOriginHeight + offsetY
        } else if offsetY > UIConstant.UI_NAV_BAR_HEIGHT {
            navigationController?.navigationBar.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT - UIConstant.UI_NAV_BAR_HEIGHT
            tableView.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT
            tableView.frame.size.height = tableViewOriginHeight + UIConstant.UI_NAV_BAR_HEIGHT + UIConstant.UI_STATUSBAR_HEIGHT
        } else {
            navigationController?.navigationBar.frame.origin.y = UIConstant.UI_STATUSBAR_HEIGHT
            tableView.frame.origin.y = UIConstant.UI_NAV_BAR_HEIGHT + UIConstant.UI_STATUSBAR_HEIGHT
            tableView.frame.size.height = tableViewOriginHeight
        }
        
    }

最后感謝您的閱讀，筆者是 iOS 開發(fā)新人（苦逼自學(xué)中...），有錯誤的地方請大家指出，共同進步。