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iosswiftuiscrollviewuikit

Unable to detect tap in UIScrollView inside another UIScrollView

I have a vertical scrolling UIScrollView which spans the entire ViewController, which contains this ContentView (UIView), so I am able to detect touch event outside of the scrollViews bounds:

import UIKit

class ContentView: UIView {
    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        let reversedSubviews = subviews.reversed()
        let hitSubview = reversedSubviews
            .first(where: { $0.hitTest(convert(point, to: $0), with: event) != nil })
        if hitSubview != nil {
            return hitSubview
        }
        return super.hitTest(point, with: event)
    }
}

This is the View hiearchey

UIScrollView (vertical scroll) //Works
|
 -- ContentView(UIView)
    |
    --UIScrollView (horizontal scroll) //Works
       |
       -- UIView
          |
          --UIButton //This does not work
    |
    --UIScrollView (horizontal scroll) //Works
       |
       -- UIView
          |
          --UIButton //This does not work

Inside this ContentView I have several other horizontal scrolling UIScrollViews. But I am not able to detect touch events inside these scrollViews, because of the ContentView.

How should I approach this to be able to detect touch event in all scrollViews, even if subviews are out of bounds?

It does not help to put ContentView inside horizontal scrollViews..

Solution

  • Here's a pretty basic example.

    Following your hierarchy:

      Main View
  |
  -- UIScrollView (vertical scroll) - Red
    |
     -- ContentView(UIView) - Medium Blue
        |
        -- UIScrollView (horizontal scroll) - Green
           |
           -- UIView - Light Gray
              |
              -- UIButton - Blue
           |
           -- UIView - Light Gray
              |
              -- UIButton - Blue
        |
        -- UIScrollView (horizontal scroll) - Green
           |
           -- UIView - Light Gray
              |
              -- UIButton - Blue
           |
           -- UIView - Light Gray
              |
              -- UIButton - Blue
        |

    This is how it looks - buttons can be tapped:

    enter image description here

    and, after scrolling down and scrolling each horizontal scroll view to the right:

    enter image description here

    Example code... no @IBOutlet or @IBAction connections needed, just assign a view controller's class to MultiScrollViewController:

    class MultiScrollViewController: UIViewController {
    
    let vertScrollView = UIScrollView()
    
    let contentView = UIView()
    
    let hScrollA = UIScrollView()
    let hScrollB = UIScrollView()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        [vertScrollView, contentView, hScrollA, hScrollB].forEach {
            $0.translatesAutoresizingMaskIntoConstraints = false
        }
        
        contentView.addSubview(hScrollA)
        contentView.addSubview(hScrollB)
        
        vertScrollView.addSubview(contentView)
        
        view.addSubview(vertScrollView)
        
        let g = view.safeAreaLayoutGuide
        let svContentG = vertScrollView.contentLayoutGuide
        let svFrameG = vertScrollView.frameLayoutGuide
        
        NSLayoutConstraint.activate([
            
            // vertical scroll view with 20-pts on each side for "padding"
            vertScrollView.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
            vertScrollView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 20.0),
            vertScrollView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -20.0),
            vertScrollView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -20.0),
            
            // content view Top / Leading / Bottom 12-pts to content layout guide
            contentView.topAnchor.constraint(equalTo: svContentG.topAnchor, constant: 12.0),
            contentView.leadingAnchor.constraint(equalTo: svContentG.leadingAnchor, constant: 12.0),
            contentView.bottomAnchor.constraint(equalTo: svContentG.bottomAnchor, constant: -12.0),
            // content view Trailing to content layout guide
            contentView.trailingAnchor.constraint(equalTo: svContentG.trailingAnchor, constant: 0.0),
            
            // content view Width: scroll frame width minus 24-pts (we don't want horizontal scrolling)
            contentView.widthAnchor.constraint(equalTo: svFrameG.widthAnchor, constant: -24.0),
            
            // horizontal scroll view A Top / Leading / Trailing 8-pts to contentView
            hScrollA.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 8.0),
            hScrollA.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 8.0),
            hScrollA.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -8.0),
            
            // horizontal scroll view B Top 20-pts from Bottom of hScrollA
            hScrollB.topAnchor.constraint(equalTo: hScrollA.bottomAnchor, constant: 20.0),
            
            // horizontal scroll view B Leading / Trailing / Bottom 8-pts to contentView
            hScrollB.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 8.0),
            hScrollB.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -8.0),
            hScrollB.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8.0),
            
            // so we have some vertical scrolling, make each horizontal scroll view
            //  60% the height of the vertical scroll view frame
            hScrollA.heightAnchor.constraint(equalTo: svFrameG.heightAnchor, multiplier: 0.6),
            hScrollB.heightAnchor.constraint(equalTo: hScrollA.heightAnchor),
            
        ])
        
        // each horizontal scroll view will have
        //  two UIViews, each with a UIButton
        
        let btn1inA = UIButton()
        let btn2inA = UIButton()
        
        let btn1inB = UIButton()
        let btn2inB = UIButton()
        
        let btn1inAView = UIView()
        let btn2inAView = UIView()
        
        let btn1inBView = UIView()
        let btn2inBView = UIView()
        
        let btnViews = [btn1inAView, btn2inAView, btn1inBView, btn2inBView]
        
        let btns = [btn1inA, btn2inA, btn1inB, btn2inB]
        let ttls = ["Button 1 in A", "Button 2 in A", "Button 1 in B", "Button 2 in B"]
        
        for (btn, str) in zip(btns, ttls) {
            btn.setTitle(str, for: [])
            btn.setTitleColor(.white, for: .normal)
            btn.setTitleColor(.gray, for: .highlighted)
            btn.titleLabel?.font = .boldSystemFont(ofSize: 18)
            btn.backgroundColor = .blue
            btn.contentEdgeInsets = UIEdgeInsets(top: 8, left: 16, bottom: 8, right: 16)
            btn.translatesAutoresizingMaskIntoConstraints = false
            btn.addTarget(self, action: #selector(self.btnTap(_:)), for: .touchUpInside)
        }
        
        for (btn, v) in zip(btns, btnViews) {
            v.backgroundColor = UIColor(white: 0.95, alpha: 1.0)
            v.translatesAutoresizingMaskIntoConstraints = false
            v.addSubview(btn)
            // center each button in a view with 8-pts padding on all 4 sides
            NSLayoutConstraint.activate([
                btn.topAnchor.constraint(equalTo: v.topAnchor, constant: 8.0),
                btn.leadingAnchor.constraint(equalTo: v.leadingAnchor, constant: 8.0),
                btn.trailingAnchor.constraint(equalTo: v.trailingAnchor, constant: -8.0),
                btn.bottomAnchor.constraint(equalTo: v.bottomAnchor, constant: -8.0),
            ])
        }
        
        // add button-holding-views to horizontal scroll views
        hScrollA.addSubview(btn1inAView)
        hScrollA.addSubview(btn2inAView)
        
        hScrollB.addSubview(btn1inBView)
        hScrollB.addSubview(btn2inBView)
        
        let svAContentG = hScrollA.contentLayoutGuide
        let svAFrameG = hScrollA.frameLayoutGuide
        
        let svBContentG = hScrollB.contentLayoutGuide
        let svBFrameG = hScrollB.frameLayoutGuide
        
        NSLayoutConstraint.activate([
            
            // button 1 in hScroll A
            //  top == content top + 20
            btn1inAView.topAnchor.constraint(equalTo: svAContentG.topAnchor, constant: 20.0),
            //  leading == content leading + 20
            btn1inAView.leadingAnchor.constraint(equalTo: svAContentG.leadingAnchor, constant: 20.0),
            
            // button 2 in hScroll A
            //  leading == button 1 leading + 600 (so we get horizontal scrolling
            btn2inAView.leadingAnchor.constraint(equalTo: btn1inAView.trailingAnchor, constant: 600.0),
            
            //  trailing == content trailing - 20
            btn2inAView.trailingAnchor.constraint(equalTo: svAContentG.trailingAnchor, constant: -20.0),
            
            //  bottom to content bottom
            btn2inAView.bottomAnchor.constraint(equalTo: svAContentG.bottomAnchor),
            
            //  bottom 20-pts from hScroll A frame bottom (so it's at lower-right)
            btn2inAView.bottomAnchor.constraint(equalTo: svAFrameG.bottomAnchor, constant: -20.0),
            
            // button 1 in hScroll B
            //  top == content top + 20
            btn1inBView.topAnchor.constraint(equalTo: svBContentG.topAnchor, constant: 20.0),
            
            //  leading == content leading + 20
            btn1inBView.leadingAnchor.constraint(equalTo: svBContentG.leadingAnchor, constant: 20.0),
            
            // button 2 in hScroll A
            //  leading == button 1 leading + 600 (so we get horizontal scrolling
            btn2inBView.leadingAnchor.constraint(equalTo: btn1inBView.trailingAnchor, constant: 600.0),
            
            //  trailing == content trailing - 20
            btn2inBView.trailingAnchor.constraint(equalTo: svBContentG.trailingAnchor, constant: -20.0),
            
            //  bottom to content bottom
            btn2inBView.bottomAnchor.constraint(equalTo: svBContentG.bottomAnchor),
            
            //  bottom 20-pts from hScroll B frame bottom (so it's at lower-right)
            btn2inBView.bottomAnchor.constraint(equalTo: svBFrameG.bottomAnchor, constant: -20.0),
            
        ])
        
        // some background colors so we can see the frames
        view.backgroundColor = .yellow
        vertScrollView.backgroundColor = .red
        
        // medium blue
        contentView.backgroundColor = UIColor(red: 0.0, green: 0.5, blue: 1.0, alpha: 1.0)
        
        hScrollA.backgroundColor = .green
        hScrollB.backgroundColor = .green
        
    }
    
    @objc func btnTap(_ sender: UIButton) -> Void {
        print(sender.currentTitle ?? "No Button Title")
    }
    
}