- 调用系统的相机和相册，模拟应用中用户更改头像的操作。使用 UIImagePickerControllerDelegate 和 UINavigationControllerDelegate 这两个代理，并调用完成图片选择的代理方法实现头像更改：
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
imgView.image = info[UIImagePickerControllerOriginalImage] as? UIImage
dismiss(animated: true, completion: nil)
}