Swift - 滚动视图（UIScrollView）的用法

import UIKit

class ViewController: UIViewController ,UIScrollViewDelegate{
override func viewDidLoad() {
    super.viewDidLoad()
    var SCREEN_WIDTH  = self.view.frame.width
    var SCREEN_HIGHT = self.view.frame.height

 let scrollView = UIScrollView()
    scrollView.frame = CGRectMake(0, 260, SCREEN_WIDTH, 100)
    let imageView = UIImageView(image: UIImage(named: "hello"))
    scrollView.contentSize = imageView.bounds.size
    scrollView.addSubview(imageView)
    scrollView.delegate = self
    scrollView.showsVerticalScrollIndicator = false
    scrollView.showsHorizontalScrollIndicator = false
   //设置最大最小缩放比
    scrollView.minimumZoomScale = 0.1
    scrollView.maximumZoomScale = 3
    self.view.addSubview(scrollView)

}

  func scrollViewDidScroll(scrollView: UIScrollView) {
    print("x:\(scrollView.contentOffset.x) y:\(scrollView.contentOffset.y)")
}

//手势放大缩小
//要实现放大缩小功能，需要指定UIScrollView的允许缩放最大比例和最小比例（默认都是是1.0）。
//  同时delegate属性指定一个委托类，委托类要继承UIScrollViewDelegate协议，并在委托类中实现viewForZoomingInScrollView方法。
func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
    for subview : AnyObject in scrollView.subviews {
        if subview.isKindOfClass(UIImageView) {
            return subview as? UIView
        }
    }
    return nil
 }


}