step 1 定义图片或地图的高度，创建图片或地图视图

//地图高度
    let mapHeight:CGFloat = 200 + STATUS_HEIGHT

let frame = CGRectMake(0,SCREEN_WIDTH,SCREEN_HEIGHT)
        tableView = UITableView(frame:frame,style:.Grouped )
        tableView.backgroundView = UIImageView(image: UIImage(named: "bgImage"))
        tableView.separatorStyle = .None
        tableView.delegate = self
        tableView.dataSource = self
        self.view.addSubview(tableView)
        //地图
        mapView = MKMapView(frame:CGRectMake(0,-mapHeight,mapHeight))
        mapView!.mapType = MKMapType.Standard
        mapView!.contentMode = .ScaleAspectFill
        mapView!.clipsToBounds = true
        tableView.addSubview(self.mapView!)
        
        tableView.contentInset = UIEdgeInsetsMake(mapHeight-STATUS_HEIGHT,0)

let STATUS_HEIGHT :CGFloat = UIApplication.sharedApplication().statusBarFrame.height

scrollViewDidScroll

step 2 在scrollView 代理方法scrollViewDidScroll 中处理下拉发生的变化

方法1，适用于地图和图片

//地图下拉放大
    func scrollViewDidScroll(scrollView: UIScrollView) {
        let offsetY = scrollView.contentOffset.y
        let radius = -offsetY/mapHeight
        if(-offsetY > mapHeight){
            mapView.transform = CGAffineTransformScale(CGAffineTransformIdentity,radius,radius)
            var frame = mapView.frame
            frame.origin.y = offsetY
            mapView.frame = frame
            
        }
    }

方法2，仅适用于图片

换成图片场景，在方法1的基础上

去掉这一句

mapView.transform = CGAffineTransformScale(CGAffineTransformIdentity,radius)

frame.size.height = -offsetY