track scroll view bouncing (#525)

Author: brightsider

Examples/Samples/Sources/ContentViewControllers/DebugTableViewController.swift

@@ -53,6 +53,7 @@ class DebugTableViewController: InspectableViewController {
 
     // MARK: - Properties
 
+    var fpc: FloatingPanelController?
     var kvoObservers: [NSKeyValueObservation] = []
     private lazy var items: [String] = {
         let items = (0..<100).map { "Items \($0)" }
@@ -250,6 +251,7 @@ extension DebugTableViewController: UITableViewDataSource {
 
 extension DebugTableViewController: UITableViewDelegate {
     func scrollViewDidScroll(_ scrollView: UIScrollView) {
+        fpc?.trackingScrollViewDidScroll()
         print("TableView --- ", scrollView.contentOffset, scrollView.contentInset)
     }
 

Examples/Samples/Sources/UseCases/UseCaseController.swift

@@ -375,6 +375,7 @@ private extension FloatingPanelController {
                 self?.panGestureRecognizer.isEnabled = !tableView.isEditing
             }
             contentVC.kvoObservers.append(ob)
+            contentVC.fpc = self
             track(scrollView: contentVC.tableView)
 
         case let contentVC as NestedScrollViewController:

Sources/Controller.swift

@@ -594,6 +594,12 @@ open class FloatingPanelController: UIViewController {
             break
         }
     }
+    
+    /// Tracks the specified scroll view scrolling.
+    ///
+    public func trackingScrollViewDidScroll() {
+        floatingPanel.trackingScrollViewDidScroll()
+    }
 
     /// Cancel tracking the specify scroll view.
     ///

Sources/Core.swift

@@ -1007,6 +1007,22 @@ class Core: NSObject, UIGestureRecognizerDelegate {
     }
 
     // MARK: - ScrollView handling
+    
+    func trackingScrollViewDidScroll() {
+        guard let scrollView = scrollView else {
+            return
+        }
+        let contentOffset = scrollView.contentOffset.y
+        guard contentOffset < 0, layoutAdapter.position == .bottom, state == layoutAdapter.mostExpandedState else {
+            if surfaceView.transform != .identity {
+                surfaceView.transform = .identity
+                scrollView.transform = .identity
+            }
+            return
+        }
+        surfaceView.transform = CGAffineTransform(translationX: 0, y: -contentOffset)
+        scrollView.transform = CGAffineTransform(translationX: 0, y: contentOffset)
+    }
 
     private func lockScrollView() {
         guard let scrollView = scrollView else { return }