当我在UIScrollView中旋转视图时，经过一些旋转/缩放手势后，视图会移出UIScrollView并完全消失。只要缩放比例为1，它就可以正常工作。 我的代码需要怎么修改才能避免这种情况？
import UIKit
class ViewController: UIViewController, UIScrollViewDelegate {
let scrollView = UIScrollView(frame: UIScreen.mainScreen().bounds)
let rotationView = UIView()
override func viewDidLoad() {
super.viewDidLoad()
let imageView = UIImageView()
view.addSubview(scrollView)
scrollView.delegate = self
scrollView.minimumZoomScale = 0.5
scrollView.maximumZoomScale = 2
let mapImage = UIImage(named: "BMS2_300.jpg")
imageView.frame = CGRect(origin: CGPoint(x: 0, y: 0), size:mapImage!.size)
imageView.image = mapImage
let rotationViewframe = CGRectMake(0, 0, imageView.frame.size.width, imageView.frame.size.height)
rotationView.frame = rotationViewframe
rotationView.addSubview(imageView)
//rotationView.sizeToFit()
scrollView.addSubview(rotationView)
scrollView.contentSize = CGSize(width: rotationView.bounds.width, height: rotationView.bounds.height)
scrollView.bringSubviewToFront(rotationView)
scrollView.contentOffset = CGPoint(x: rotationView.frame.width/2, y: rotationView.frame.height/2)
let mapRotGestureRecognizer = UIRotationGestureRecognizer(target: self, action: #selector(ViewController.rotateMap(_:)))
rotationView.addGestureRecognizer(mapRotGestureRecognizer)
}
func rotateMap(sender: UIRotationGestureRecognizer) {
let radians = sender.rotation
if let senderView = sender.view {
senderView.transform = CGAffineTransformRotate(senderView.transform, radians)
sender.rotation = 0
}
}
func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
return self.rotationView
}
func scrollViewDidEndZooming(scrollView: UIScrollView, withView view: UIView?, atScale scale: CGFloat) {
scrollView.contentSize = rotationView.frame.size
}