iOS - How to pass down tap gesture without changing the underneath UIViewController?

Question

I have two view controllers, B is presented on top of A, but not full screen. I am using a UIPresentationController to custom B's frame. What I want is, when tap on A, B is dismissed and A responds to it's own tap gesture.

How to achieve this within B and the UIPresentationController, without touching A's code?

I tried to add a full screen background view for B, but don't know how to pass the tap gesture down without changing A.

Answer 1

Customize a background view, always return false for pointInside method to ignore the touch event and do whatever needed before return, such as dismiss B.

class BackgroundView: UIView {
    override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        // anything you want
        return false
    }
}

Add the custom background view to the UIPresentationController. Set containerView's isUserInteractionEnabled to false, otherwise the UITransitionView will block the touch event to pass down.

class MyPresentationController: UIPresentationController {
    var backgroundView: BackgroundView = BackgroundView()
    var containerFrame: CGRect = UIScreen.main.bounds
    
    override var frameOfPresentedViewInContainerView: CGRect {
        return CGRect(x: 0, y: 300, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height - 300)
    }
    
    override init(presentedViewController: UIViewController, presenting presentingViewController: UIViewController?) {
        super.init(presentedViewController: presentedViewController, presenting: presentingViewController)
        self.backgroundView.backgroundColor = UIColor.yellow
        self.backgroundView.alpha = 0.5
        self.backgroundView.translatesAutoresizingMaskIntoConstraints = false
    }
    
    override func presentationTransitionWillBegin() {
        self.containerView?.addSubview(self.backgroundView)
        self.containerView?.isUserInteractionEnabled = false // !!!
    }
    
    override func containerViewDidLayoutSubviews() {
        super.containerViewDidLayoutSubviews()
        self.containerView?.frame = self.containerFrame
        self.backgroundView.frame = self.containerFrame
        self.presentedView?.frame = self.frameOfPresentedViewInContainerView
    }
}