Ios 如何在pop期间设置UINavigationBar背景图像的动画

我正在尝试在pop转换期间为导航栏的背景图像设置动画

我意识到backgroundImage不是一个可设置动画的属性，但我已经能够在推送过程中通过在视图控制器的ViewWillAspect方法中使用CATTransition来实现这一点：

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    let animation = CATransition()
    animation.duration = 0.3
    animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
    animation.type = kCATransitionFade

    navigationController?.navigationBar.layer.add(animation, forKey: nil)
    navigationController?.navigationBar.setBackgroundImage(navigationBarBackgroundImage, for: .default)
}

我希望这在pop期间也能起作用，但实际上，在pop动画完成后，导航栏会突然显示下一个视图控制器（未设置动画）的背景图像

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    transitionCoordinator?.animate(alongsideTransition: { [weak self] (context) in
    let animation = CATransition()
    animation.duration = 0.3
    animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
    animation.type = kCATransitionFade

    self?.navigationController?.navigationBar.layer.add(animation, forKey: nil)
    self?.navigationController?.navigationBar.setBackgroundImage(navigationBarImage, for: .default)
    }, completion: nil)
}

我还尝试将上述尝试与过渡协调器相结合，但在pop完成后图像突然改变的情况下，它会产生完全相同的结果

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    transitionCoordinator?.animate(alongsideTransition: { [weak self] (context) in
    let animation = CATransition()
    animation.duration = 0.3
    animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
    animation.type = kCATransitionFade

    self?.navigationController?.navigationBar.layer.add(animation, forKey: nil)
    self?.navigationController?.navigationBar.setBackgroundImage(navigationBarImage, for: .default)
    }, completion: nil)
}

具体来说，我正在寻找一种在iOS9和iOS10上工作的方法