子视图未添加到cameraOverlayView

Question

此函数成功地为imagePickerController提供了overlayView。 snapButton子视图不可见。如何将子视图添加到cameraOverlayView？

func showImagePickerForSourceType(sourceType: UIImagePickerControllerSourceType){



    imagePickerController.modalPresentationStyle = UIModalPresentationStyle.CurrentContext
    imagePickerController.sourceType = sourceType
    imagePickerController.delegate = self


    if (sourceType == UIImagePickerControllerSourceType.Camera){
        imagePickerController.showsCameraControls = false

        let overlayView = UIView(frame: CGRectMake(0, self.view.frame.width, self.view.frame.width, self.view.frame.height-self.view.frame.width))
        overlayView.backgroundColor = UIColor.whiteColor()
        overlayView.alpha = 1.0 // tried this to make sure subview wasn't hiding behind
        println(overlayView)

        let snapButton = UIView(frame: CGRectMake(self.view.frame.width/2-22, self.view.frame.height-200, 44, 44))
        snapButton.layer.cornerRadius = 22
        snapButton.userInteractionEnabled = true
        snapButton.backgroundColor = UIColor.blackColor()

        overlayView.addSubview(snapButton)
        overlayView.bringSubviewToFront(snapButton)

        imagePickerController.cameraOverlayView = overlayView

    }

    self.presentViewController(self.imagePickerController, animated: true, completion: nil)
}