如何等待子视图布局在初始视图加载循环后稳定下来?

我有一个 UIViewController ,我通过嵌入 UIImageView 里面 UIScrollView .

class ZoomableImageView: UIScrollView {
    // public so that delegate can access
    public let imageView: UIImageView = {

        let _imageView = UIImageView()
        _imageView.translatesAutoresizingMaskIntoConstraints = false

        return _imageView

    } ()



     // this method will be called multiple times to display different images
    public func setImage(image: UIImage) {
        imageView.image = image

        imageView.frame = CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height)

        self.contentSize = image.size

        // gw: not working here, too early
        setZoomScale()

    }

    func setZoomScale() {


        let imageViewSize = imageView.bounds.size

        let scrollViewSize = self.bounds.size
        let widthScale = scrollViewSize.width / imageViewSize.width
        let heightScale = scrollViewSize.height / imageViewSize.height

        print("gw: imageViewSize: \(imageViewSize), scrollViewSize: \(scrollViewSize)")

        self.minimumZoomScale = min(widthScale, heightScale)
        self.maximumZoomScale = 1.2 // allow maxmum 120% of original image size

        // set initial zoom to fit the longer side (longer side ==> smaller scale)
        zoomScale = minimumZoomScale


    }

}

每次我改变 UIImage 在图像视图中,我想等待 UIIVIEVIEW 在我可以使用它计算放大比例因子之前,要确定的绑定大小 UISCLVIEW .

问题 :放在什么地方合适 setZoomScale() ?我把它放在离开之前 setImage 方法,但 imageView.bounds.size 在我的打印声明中不正确。请注意,每次图像更改时都需要触发它,而不仅仅是初始视图加载阶段。

我也试着把 setZoomScale 在视图控制器中 viewWillLayoutSubviews ,但我这里还有一个附加问题:是 视图将显示在子视图之外 在视图初始化阶段只调用一次?我能用强制触发吗 setNeedsLayout ?(我尝试过,但不重新触发视图将显示在子视图之外)