From 53884a37de498f683d600ba0b883153e4b99e9e3 Mon Sep 17 00:00:00 2001
From: Adam Barth <abarth@chromium.org>
Date: Fri, 14 Aug 2015 09:37:19 -0700
Subject: [PATCH] Generalize _cleanRelayoutSubtreeRootChildren into
 visitChildren

This generalization will let us implement other alogorithims that need to walk
the RenderObject tree.
---
 packages/flutter/lib/rendering/object.dart | 17 +++++++++++------
 packages/flutter/lib/widgets/scaffold.dart |  8 ++++++++
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/packages/flutter/lib/rendering/object.dart b/packages/flutter/lib/rendering/object.dart
index 44593fe407..ff1ddbde40 100644
--- a/packages/flutter/lib/rendering/object.dart
+++ b/packages/flutter/lib/rendering/object.dart
@@ -90,6 +90,7 @@ abstract class Constraints {
   bool get isTight;
 }
 
+typedef void RenderObjectVisitor(RenderObject child);
 typedef void LayoutCallback(Constraints constraints);
 
 abstract class RenderObject extends AbstractNode implements HitTestTarget {
@@ -125,6 +126,9 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     markNeedsLayout();
   }
 
+  // Override in subclasses with children and call the visitor for each child.
+  void visitChildren(RenderObjectVisitor visitor) { }
+
   static bool _debugDoingLayout = false;
   static bool get debugDoingLayout => _debugDoingLayout;
   bool _debugDoingThisResize = false;
@@ -193,10 +197,11 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     if (_relayoutSubtreeRoot != this) {
       _relayoutSubtreeRoot = null;
       _needsLayout = true;
-      _cleanRelayoutSubtreeRootChildren();
+      visitChildren((RenderObject child) {
+        child._cleanRelayoutSubtreeRoot();
+      });
     }
   }
-  void _cleanRelayoutSubtreeRootChildren() { } // workaround for lack of inter-class mixins in Dart
   void scheduleInitialLayout() {
     assert(attached);
     assert(parent == null);
@@ -541,9 +546,9 @@ abstract class RenderObjectWithChildMixin<ChildType extends RenderObject> implem
     if (_child != null)
       _child.detach();
   }
-  void _cleanRelayoutSubtreeRootChildren() {
+  void visitChildren(RenderObjectVisitor visitor) {
     if (_child != null)
-      _child._cleanRelayoutSubtreeRoot();
+      visitor(_child);
   }
   String debugDescribeChildren(String prefix) {
     if (child != null)
@@ -734,10 +739,10 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
       child = child.parentData.nextSibling;
     }
   }
-  void _cleanRelayoutSubtreeRootChildren() {
+  void visitChildren(RenderObjectVisitor visitor) {
     ChildType child = _firstChild;
     while (child != null) {
-      child._cleanRelayoutSubtreeRoot();
+      visitor(child);
       assert(child.parentData is ParentDataType);
       child = child.parentData.nextSibling;
     }
diff --git a/packages/flutter/lib/widgets/scaffold.dart b/packages/flutter/lib/widgets/scaffold.dart
index 10d205c408..0cc60460ae 100644
--- a/packages/flutter/lib/widgets/scaffold.dart
+++ b/packages/flutter/lib/widgets/scaffold.dart
@@ -70,6 +70,14 @@ class RenderScaffold extends RenderBox {
     }
   }
 
+  void visitChildren(RenderObjectVisitor visitor) {
+    for (ScaffoldSlots slot in ScaffoldSlots.values) {
+      RenderBox box = _slots[slot];
+      if (box != null)
+        visitor(box);
+    }
+  }
+
   ScaffoldSlots remove(RenderBox child) {
     assert(child != null);
     for (ScaffoldSlots slot in ScaffoldSlots.values) {