From 217394abaf0d9a77ffbfc36ad20e60015830b502 Mon Sep 17 00:00:00 2001
From: Shin Yamamoto <shin@scenee.com>
Date: Wed, 6 Jan 2021 18:57:57 +0900
Subject: [PATCH] Prevent the potential memory leaks in the modal transition

This dismisses the frame 'FloatingPanel Core.move(from:to:animated:completion:)'
in the following memory leaks

> BoardServices -[BSXPCServiceConnectionEventHandler remoteTarget]
> BoardServices __63+[BSXPCServiceConnectionProxy createImplementationForProtocol:]_block_invoke

These leaks happens when a panel showes and hides using "Show Multi Panel Modal"
in the Samples app.
---
 Sources/Core.swift          | 25 +++++++++++++++++++------
 Sources/Transitioning.swift | 30 ++++++++++++++++++++++++++----
 2 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/Sources/Core.swift b/Sources/Core.swift
index f277117b..59b4e01c 100644
--- a/Sources/Core.swift
+++ b/Sources/Core.swift
@@ -32,7 +32,8 @@ class Core: NSObject, UIGestureRecognizerDelegate {
     let panGestureRecognizer: FloatingPanelPanGestureRecognizer
     var isRemovalInteractionEnabled: Bool = false
 
-    fileprivate var animator: UIViewPropertyAnimator?
+    fileprivate var isSuspended: Bool = false // Prevent a memory leak in the modal transition
+    fileprivate var transitionAnimator: UIViewPropertyAnimator?
     fileprivate var moveAnimator: NumericSpringAnimator?
 
     private var initialSurfaceLocation: CGPoint = .zero
@@ -158,12 +159,15 @@ class Core: NSObject, UIGestureRecognizerDelegate {
             animator.addCompletion { [weak self] _ in
                 guard let self = self else { return }
 
-                self.animator = nil
+                self.transitionAnimator = nil
                 updateScrollView()
                 self.ownerVC?.notifyDidMove()
                 completion?()
             }
-            self.animator = animator
+            self.transitionAnimator = animator
+            if isSuspended {
+                return
+            }
             animator.startAnimation()
         } else {
             self.state = to
@@ -376,7 +380,7 @@ class Core: NSObject, UIGestureRecognizerDelegate {
                 if interactionInProgress {
                     lockScrollView()
                 } else {
-                    if state == layoutAdapter.edgeMostState, self.animator == nil {
+                    if state == layoutAdapter.edgeMostState, self.transitionAnimator == nil {
                         switch layoutAdapter.position {
                         case .top, .left:
                             if offsetDiff < 0 && velocity > 0 {
@@ -496,7 +500,7 @@ class Core: NSObject, UIGestureRecognizerDelegate {
             animator.stopAnimation(true)
             endAttraction(false)
         }
-        if let animator = self.animator {
+        if let animator = self.transitionAnimator {
             guard 0 >= layoutAdapter.offsetFromEdgeMost else { return }
             log.debug("a panel animation(interruptible: \(animator.isInterruptible)) interrupted!!!")
             if animator.isInterruptible {
@@ -1037,7 +1041,7 @@ public final class FloatingPanelPanGestureRecognizer: UIPanGestureRecognizer {
     public override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent) {
         super.touchesBegan(touches, with: event)
         initialLocation = touches.first?.location(in: view) ?? .zero
-        if floatingPanel?.animator != nil || floatingPanel?.moveAnimator != nil {
+        if floatingPanel?.transitionAnimator != nil || floatingPanel?.moveAnimator != nil {
             self.state = .began
         }
     }
@@ -1198,3 +1202,12 @@ private class NumericSpringAnimator: NSObject {
         v = (v + h * o2 * (xt - x)) / det
     }
 }
+
+extension FloatingPanelController {
+    func suspendTransitionAnimator(_ suspended: Bool) {
+        self.floatingPanel.isSuspended = suspended
+    }
+    var transitionAnimator: UIViewPropertyAnimator? {
+        return self.floatingPanel.transitionAnimator
+    }
+}
diff --git a/Sources/Transitioning.swift b/Sources/Transitioning.swift
index 677f3b61..bb93321b 100644
--- a/Sources/Transitioning.swift
+++ b/Sources/Transitioning.swift
@@ -90,14 +90,25 @@ class ModalPresentTransition: NSObject, UIViewControllerAnimatedTransitioning {
         return TimeInterval(animator.duration)
     }
 
-    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
+    func interruptibleAnimator(using transitionContext: UIViewControllerContextTransitioning) -> UIViewImplicitlyAnimating {
         guard
             let fpc = transitionContext.viewController(forKey: .to) as? FloatingPanelController
         else { fatalError() }
 
-        fpc.show(animated: true) {
+        if let animator = fpc.transitionAnimator {
+            return animator
+        }
+
+        fpc.suspendTransitionAnimator(true)
+        fpc.show(animated: true) { [weak fpc] in
+            fpc?.suspendTransitionAnimator(false)
             transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
         }
+        return fpc.transitionAnimator!
+    }
+
+    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
+        self.interruptibleAnimator(using: transitionContext).startAnimation()
     }
 }
 
@@ -111,14 +122,25 @@ class ModalDismissTransition: NSObject, UIViewControllerAnimatedTransitioning {
         return TimeInterval(animator.duration)
     }
 
-    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
+    func interruptibleAnimator(using transitionContext: UIViewControllerContextTransitioning) -> UIViewImplicitlyAnimating {
         guard
             let fpc = transitionContext.viewController(forKey: .from) as? FloatingPanelController
         else { fatalError() }
 
-        fpc.hide(animated: true) {
+        if let animator = fpc.transitionAnimator {
+            return animator
+        }
+
+        fpc.suspendTransitionAnimator(true)
+        fpc.hide(animated: true) { [weak fpc] in
+            fpc?.suspendTransitionAnimator(false)
             transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
         }
+        return fpc.transitionAnimator!
+    }
+
+    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
+        self.interruptibleAnimator(using: transitionContext).startAnimation()
     }
 }