Support visibility events in ASScrollNode (#2799)

* Support visibility events in ASScrollNode

* Sort imports in ASScrollNode.mm

Author: nguyenhuy

AsyncDisplayKit/ASScrollNode.mm

@@ -9,6 +9,8 @@
 //
 
 #import "ASScrollNode.h"
+#import "ASDisplayNodeExtras.h"
+#import "ASDisplayNode+FrameworkPrivate.h"
 #import "ASDisplayNode+FrameworkSubclasses.h"
 #import "ASLayout.h"
 #import "_ASDisplayLayer.h"
@@ -24,6 +26,32 @@ + (Class)layerClass
   return [_ASDisplayLayer class];
 }
 
+- (ASScrollNode *)scrollNode
+{
+  return (ASScrollNode *)ASViewToDisplayNode(self);
+}
+
+#pragma mark - _ASDisplayView behavior substitutions
+// Need these to drive interfaceState so we know when we are visible, if not nested in another range-managing element.
+// Because our superclass is a true UIKit class, we cannot also subclass _ASDisplayView.
+- (void)willMoveToWindow:(UIWindow *)newWindow
+{
+  ASDisplayNode *node = self.scrollNode; // Create strong reference to weak ivar.
+  BOOL visible = (newWindow != nil);
+  if (visible && !node.inHierarchy) {
+    [node __enterHierarchy];
+  }
+}
+
+- (void)didMoveToWindow
+{
+  ASDisplayNode *node = self.scrollNode; // Create strong reference to weak ivar.
+  BOOL visible = (self.window != nil);
+  if (!visible && node.inHierarchy) {
+    [node __exitHierarchy];
+  }
+}
+
 @end
 
 @implementation ASScrollNode