问IOS Swift imagePickerController未调用

EN

class MyPage: UIViewController,UIImagePickerControllerDelegate,UINavigationControllerDelegate {

    var imagePicker = UIImagePickerController()
    @IBOutlet weak var selectImage: UIButton!

    override func viewDidLoad() {
        imagePicker.sourceType = .photoLibrary
        imagePicker.delegate = self
    }



   @IBAction func selectImage(_ sender: Any) {
            print("a")
            if UIImagePickerController.isSourceTypeAvailable(.photoLibrary){
                print("b")
                imagePicker.allowsEditing = false
                imagePicker.mediaTypes = UIImagePickerController.availableMediaTypes(for: .photoLibrary)!
                self.present(imagePicker, animated: true,completion: nil)
            }
    @objc func imagePickerController(picker: UIImagePickerController!, didFinishPickingImage image: UIImage!, editingInfo: NSDictionary!){
            self.dismiss(animated: true, completion: { () -> Void in
                print("dismiss")
            })

            print(image)
            selectImage.setImage(image, for: .normal)
        }
}