WillShowViewControllerExample.swift

class GeneralVC: ParentVC, UIActionSheetDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate {

    @IBAction func customPickerButtonPressed(sender: AnyObject) {
        let picker = UIImagePickerController()
        picker.delegate = self
        picker.sourceType = UIImagePickerControllerSourceType.PhotoLibrary
        picker.allowsEditing = true

        self.presentViewController(picker, animated: true, completion: nil)
    }
    
    func navigationController(navigationController: UINavigationController, willShowViewController viewController: UIViewController, animated: Bool) {
        // we need to do it there
        if let imagePicker = navigationController as? UIImagePickerController,
            let navItem = imagePicker.navigationBar.topItem {
            navItem.backBarButtonItem = createEmptyButton()
            navItem.rightBarButtonItem = createEmptyButton()
            navItem.leftBarButtonItems = createBackButtonWithFn({ [unowned imagePicker] in imagePicker.dismissViewControllerAnimated(true, completion: nil) })
        }
    }

    func imagePickerController(picker: UIImagePickerController, didFinishPickingImage image: UIImage!, editingInfo: [NSObject : AnyObject]!) {
        picker.dismissViewControllerAnimated(true, completion: nil)
    }
}