Allow multiple scroll views inside a navigation controller

SheetImagePicker/SheetContainerViewController.swift

@@ -56,6 +56,8 @@ public class SheetContainerViewController: UIViewController {
     var contentScrollView: UIScrollView? {
         delegate?.sheetContainerContentScrollView(self) ?? content.view as? UIScrollView
     }
+    var initialScrollViewContentOffset: CGPoint?
+    var scrollViewIsMovingSheet = false
 
     public init(content: UIViewController) {
         self.content = content
@@ -100,6 +102,10 @@ public class SheetContainerViewController: UIViewController {
         panGesture.delegate = self
         content.view.addGestureRecognizer(panGesture)
         
+        contentScrollViewChanged()
+    }
+    
+    public func contentScrollViewChanged() {
         if let scrollView = contentScrollView {
             scrollView.panGestureRecognizer.addTarget(self, action: #selector(scrollViewPanGestureRecognized))
         }
@@ -134,14 +140,23 @@ public class SheetContainerViewController: UIViewController {
         let shouldMoveSheetUp = topConstraint.constant > topDetent.offset && velocity.y < 0 // not fully expanded and dragging up
 
         let shouldMoveSheet = shouldMoveSheetDown || shouldMoveSheetUp
-        if shouldMoveSheet {
-            scrollView.bounces = false
-            scrollView.setContentOffset(CGPoint(x: 0, y: topContentOffset), animated: false)
-        }
 
         switch recognizer.state {
-        case .changed:
+        case .began:
+            scrollView.bounces = false
+            scrollViewIsMovingSheet = shouldMoveSheet
             if shouldMoveSheet {
+                initialScrollViewContentOffset = scrollView.contentOffset
+            }
+            
+        case .changed:
+            scrollViewIsMovingSheet = scrollViewIsMovingSheet || shouldMoveSheet
+            if scrollViewIsMovingSheet {
+                if initialScrollViewContentOffset == nil {
+                    initialScrollViewContentOffset = scrollView.contentOffset
+                }
+                scrollView.setContentOffset(initialScrollViewContentOffset!, animated: false)
+                
                 let translation = recognizer.translation(in: scrollView)
                 setTopOffset(topConstraint.constant + translation.y)
                 recognizer.setTranslation(.zero, in: scrollView)
@@ -149,9 +164,12 @@ public class SheetContainerViewController: UIViewController {
 
         case .ended:
             scrollView.bounces = true
-            if shouldMoveSheet {
+            if scrollViewIsMovingSheet {
+                scrollView.setContentOffset(initialScrollViewContentOffset!, animated: false)
                 springToNearestDetent(verticalVelocity: velocity.y)
             }
+            scrollViewIsMovingSheet = false
+            initialScrollViewContentOffset = nil
 
         default:
             break
@@ -165,8 +183,8 @@ public class SheetContainerViewController: UIViewController {
         if offset < topOffset {
             let smoothed = smoothstep(value: offset, from: topOffset, to: 0)
             offset = topOffset - smoothed * maximumStretchDistance
-            
         }
+        
         topConstraint.constant = offset
         dimmingView.alpha = lerp(offset, min: topOffset, max: bottomDetent.offset, from: maximumDimmingAlpha, to: minimumDimmingAlpha)
     }

SheetImagePickerTest/ContentTableViewController.swift

@@ -44,6 +44,9 @@ class ContentTableViewController: UITableViewController {
     override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
         guard let navController = navigationController else { return }
         
+        navController.pushViewController(ContentTableViewController(), animated: true)
+        return
+        
         let vc = UIViewController()
         vc.view.backgroundColor = .systemBackground
         let label = UILabel()

SheetImagePickerTest/ViewController.swift

@@ -11,6 +11,8 @@ import SheetImagePicker
 
 class ViewController: UIViewController {
     
+    var sheet: SheetContainerViewController!
+
     override func viewDidLoad() {
         super.viewDidLoad()
         // Do any additional setup after loading the view.
@@ -37,7 +39,7 @@ class ViewController: UIViewController {
             label.centerYAnchor.constraint(equalTo: blurView.contentView.centerYAnchor)
         ])
 
-        let sheet = SheetContainerViewController(content: content)
+        sheet = SheetContainerViewController(content: content)
         sheet.delegate = self
         sheet.detents = [.bottom, .middle, .top]
         
@@ -50,7 +52,7 @@ class ViewController: UIViewController {
         content.view.layer.masksToBounds = true
         content.view.layer.cornerRadius = view.bounds.width * 0.02
         
-        let sheet = SheetContainerViewController(content: content)
+        sheet = SheetContainerViewController(content: content)
         sheet.delegate = self
         sheet.detents = [.bottom, .middle, .top]
         
@@ -74,7 +76,7 @@ class ViewController: UIViewController {
         nav.view.layer.masksToBounds = true
         nav.view.layer.cornerRadius = view.bounds.width * 0.02
 
-        let sheet = SheetContainerViewController(content: nav)
+        sheet = SheetContainerViewController(content: nav)
         sheet.delegate = self
         sheet.detents = [.bottom, .middle, .top]
         
@@ -85,11 +87,12 @@ class ViewController: UIViewController {
         let table = ContentTableViewController()
         
         let nav = UINavigationController(rootViewController: table)
+        nav.delegate = self
         nav.view.translatesAutoresizingMaskIntoConstraints = false
         nav.view.layer.masksToBounds = true
         nav.view.layer.cornerRadius = view.bounds.width * 0.02
         
-        let sheet = SheetContainerViewController(content: nav)
+        sheet = SheetContainerViewController(content: nav)
         sheet.delegate = self
         sheet.detents = [.bottom, .middle, .top]
         
@@ -120,3 +123,9 @@ extension ViewController: SheetContainerViewControllerDelegate {
         }
     }
 }
+
+extension ViewController: UINavigationControllerDelegate {
+    func navigationController(_ navigationController: UINavigationController, didShow viewController: UIViewController, animated: Bool) {
+        sheet.contentScrollViewChanged()
+    }
+}