Breaking a retain cycle between RCTSurfaceTouchHandler and RCTFabricSurface (another approach)

Summary:
This is a different approach to break the retain cycle: instead of detaching a view manually, we store a pointer to a view weakly.

I am working on some change that will make possible (and make use of it) to call `start` and `stop` on Surface objects mutiple times, so to make it happens we need to remove detaching from `stop` method.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D24041524

fbshipit-source-id: 700b13d715d2eb84d52bf3e51e0fd2896a55baf8

React/Fabric/RCTSurfaceTouchHandler.h

@@ -11,6 +11,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface RCTSurfaceTouchHandler : UIGestureRecognizer
 
+/*
+ * Attaches (and detaches) a view to the touch handler.
+ * The receiver does not retain the provided view.
+ */
 - (void)attachToView:(UIView *)view;
 - (void)detachFromView:(UIView *)view;
 

React/Fabric/RCTSurfaceTouchHandler.mm

@@ -159,7 +159,10 @@ struct PointerHasher {
   std::unordered_map<__unsafe_unretained UITouch *, ActiveTouch, PointerHasher<__unsafe_unretained UITouch *>>
       _activeTouches;
 
-  UIView *_rootComponentView;
+  /*
+   * We hold the view weakly to prevent a retain cycle.
+   */
+  __weak UIView *_rootComponentView;
   IdentifierPool<11> _identifierPool;
 }
 

React/Fabric/Surface/RCTFabricSurface.mm

@@ -83,7 +83,6 @@ using namespace facebook::react;
   }
 
   [_surfacePresenter unregisterSurface:self];
-  [_touchHandler detachFromView:_view];
   return YES;
 }