//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celllet 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cellvar 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))}}