ios实践之tableView顶部“弹簧”图片

大家可能注意到有些tableView的顶部图片，会随着你拉伸而跟着拉伸变大。
一种思路是将图片放置tableView的tableHeaderView上当tablview下移改变图片的frame达到效果。当然这个效果特别简单，高手可以略过。

import UIKitclass ViewController: UIViewController,UITableViewDataSource,UITableViewDelegate {lazy var myTableView : UITableView! = {var  tableView = UITableView.init(frame: self.view.frame,style:UITableViewStyle.plain)tableView.delegate = selftableView.dataSource = selftableView.register(UITableViewCell.classForCoder(), forCellReuseIdentifier: "mycell")return tableView}()var headerImageView:UIImageView?var headerView:UIView?var headerViewHeight:CGFloat = 0.0override func viewDidLoad() {super.viewDidLoad()// Do any additional setup after loading the view, typically from a nib.setupUI()}func  setupUI(){headerView = UIView.init(frame: CGRect(x:0,y:0,width:self.view.frame.width,height:300))headerViewHeight = headerView!.frame.height;self.view.addSubview(headerView!)headerImageView = UIImageView.init(frame: headerView!.frame)headerImageView?.image = UIImage.init(named: "bg-mine")headerView?.addSubview(headerImageView!)myTableView.tableHeaderView = headerViewself.view.addSubview(myTableView)}func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {return 2}func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {let cell:UITableViewCell = tableView.dequeueReusableCell(withIdentifier: "mycell", for: indexPath)cell.textLabel?.text = "测试"return cell}func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {return 50}func scrollViewDidScroll(_ scrollView: UIScrollView) {let  contentOffSetY = scrollView.contentOffset.yif  contentOffSetY < 0 {var rect = headerView?.framerect?.size.height = headerViewHeight - contentOffSetYlet headerViewWidth = headerView?.frame.size.widthrect?.size.width = headerViewWidth!*(headerViewHeight-contentOffSetY)/headerViewHeightrect?.origin.x = -((rect?.size.width)! - headerViewWidth!)/2rect?.origin.y = contentOffSetYheaderView?.frame = rect!headerImageView?.frame = rect!}  }
}