//懒加载    
　　//顶部需要拉伸自定义视图

    lazy var headView:MyHeaderView = {

        //let hframe = CGRect(x: 0, y: 0, width: swidth, height: swidth/self.imgRation)

        // let hview = Bundle.main.loadNibNamed("MyInfoHeaderView", owner: nil, options: nil)?.first as! MyInfoHeaderView

        //return hview;

    }()

    //MARK:1)集合视图

    self.collectionView?.addSubview(self.headView) 

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt     indexPath: IndexPath) -> UICollectionViewCell {

        if indexPath.section == 0 { //顶部返回一个空的cell

            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)

            return cell

        }

    ....

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

        if indexPath.section == 0  {//顶部

            return CGSize(width: swidth, height:200.0 )

        }

....

      //MARK:2)列表视图

    self.tableView?.addSubview(self.headView)  

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        if indexPath.section == 0 { //顶部返回一个空的cell

            var cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier)

            return cell!

        }

....

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {

        if indexPath.section == 0{

            return 200.0;

        }

....

    //MARK:拉伸效果实现位置

    override func scrollViewDidScroll(_ scrollView: UIScrollView) {

        let point = scrollView.contentOffset;

        if point.y <= 0 {//下拉

            //self.headView.frame.size.height = swidth/imgRation - point.y

            //self.headView.frame.size.width = self.headView.frame.size.height*imgRation

            //self.headView.frame.origin.x = (swidth - self.headView.frame.size.width)/2

            //self.headView.frame.origin.y =  point.y

            //self.headView.titleImgLeft.constant = 18 - self.headView.frame.origin.x

            //self.mainNavView.backgroundColor = UIColor.clear

            //self.mainNavView.searImg.image = UIImage(named: "搜索框r")

        }else{//上推

           //if point.y >= (self.headView.frame.height - 64){

                //self.mainNavView.searImg.image = UIImage(named: "搜索框w")

                //self.mainNavView.searchText.backgroundColor = UIColor.white

            //}

            //self.headView.titleImgLeft.constant = 18

            // self.mainNavView.backgroundColor = UIColor(red:245/255.0, green:74/255.0, blue:48/255.0, alpha: point.y/(self.headView.frame.height - 64))

        }

    }