How do you pass a gesture between subviews in UIKit? - ios

Question

I've got a ViewController with three subviews. I'm trying to get them to detect touches in their bounds from a starting point outside their bounds without the user lifting their finger (ie the user dragging into the view). I thought hitTest would do this but it only works for separate taps. I assume this is probably passing a gesture through instead but I've not found out how to implement this.
class SuperViewController: UIViewController {
var view01 = UIView(frame: CGRect(x: 0, y: 0, width: 1000,
height: 800))
var view02 = UIView(frame: CGRect(x: 0, y: 0, width: 600,
height: 400))
let view03 = UIView(frame: CGRect(x: 0, y: 0, width: 300,
height: 200))
override func viewDidLoad() {
super.viewDidLoad()
self.view = TestView()
view01.backgroundColor = .orange
view02.backgroundColor = .blue
view03.backgroundColor = .green
self.view.addSubview(view01)
self.view.addSubview(view02)
self.view.addSubview(view03)
}
}
Which produces this
And then I've subclassed UIView for the SuperViewController's view.
class TestView: UIView {
override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
guard self.isUserInteractionEnabled, !isHidden, alpha > 0.01 else {return nil}
if self.point(inside: point, with: event) {
for subview in subviews.reversed() {
let hitView = subview.hitTest(point, with: event)
if hitView != nil {
hitView?.backgroundColor = .red
return hitView
}
}
return self
}
return nil
}
}
So each one turns red when the user taps. But ideally I want them to each respond with one drag from the top left corner of the screen to the other.

Answer 1

You can accomplish this with a UIPanGestureRecognizer.
Here's an example below:
class ViewController: UIViewController {
var view01 = UIView(frame: CGRect(x: 0, y: 0, width: 1000,
height: 800))
var view02 = UIView(frame: CGRect(x: 0, y: 0, width: 600,
height: 400))
let view03 = UIView(frame: CGRect(x: 0, y: 0, width: 300,
height: 200))
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
view01.backgroundColor = .orange
view02.backgroundColor = .blue
view03.backgroundColor = .green
self.view.addSubview(view01)
self.view.addSubview(view02)
self.view.addSubview(view03)
let gestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(handlePan))
self.view.addGestureRecognizer(gestureRecognizer)
}
#objc
private func handlePan(_ gestureRecognizer: UIPanGestureRecognizer) {
guard let view = gestureRecognizer.view else {
return
}
let translation = gestureRecognizer.translation(in: view)
for subview in view.subviews.reversed() {
if let hitView = subview.hitTest(translation, with: nil) {
hitView.backgroundColor = .red
return
}
}
}
}