From 06af2f7d156e3c347a001c868a648775b26acdfd Mon Sep 17 00:00:00 2001
From: Hans Muller <hansmuller@chromium.org>
Date: Fri, 26 Jun 2015 11:17:31 -0700
Subject: [PATCH] Add RenderObject.childCount

R=ianh@google.com

Review URL: https://codereview.chromium.org/1217533002.
---
 sdk/lib/rendering/object.dart |  8 +++++++-
 sdk/lib/widgets/tabs.dart     | 17 -----------------
 2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/sdk/lib/rendering/object.dart b/sdk/lib/rendering/object.dart
index a21db014216..f899d31bedd 100644
--- a/sdk/lib/rendering/object.dart
+++ b/sdk/lib/rendering/object.dart
@@ -367,7 +367,6 @@ abstract class ContainerParentDataMixin<ChildType extends RenderObject> {
 }
 
 abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, ParentDataType extends ContainerParentDataMixin<ChildType>> implements RenderObject {
-  // abstract class that has only InlineNode children
 
   bool _debugUltimatePreviousSiblingOf(ChildType child, { ChildType equals }) {
     assert(child.parentData is ParentDataType);
@@ -388,12 +387,17 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
     return child == equals;
   }
 
+  int _childCount = 0;
+  int get childCount => _childCount;
+
   ChildType _firstChild;
   ChildType _lastChild;
   void _addToChildList(ChildType child, { ChildType before }) {
     assert(child.parentData is ParentDataType);
     assert(child.parentData.nextSibling == null);
     assert(child.parentData.previousSibling == null);
+    _childCount += 1;
+    assert(_childCount > 0);
     if (before == null) {
       // append at the end (_lastChild)
       child.parentData.previousSibling = _lastChild;
@@ -448,6 +452,8 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
     assert(child.parentData is ParentDataType);
     assert(_debugUltimatePreviousSiblingOf(child, equals: _firstChild));
     assert(_debugUltimateNextSiblingOf(child, equals: _lastChild));
+    _childCount -= 1;
+    assert(_childCount > 0);
     if (child.parentData.previousSibling == null) {
       assert(_firstChild == child);
       _firstChild = child.parentData.nextSibling;
diff --git a/sdk/lib/widgets/tabs.dart b/sdk/lib/widgets/tabs.dart
index 741594d2bf5..a0b615f39a8 100644
--- a/sdk/lib/widgets/tabs.dart
+++ b/sdk/lib/widgets/tabs.dart
@@ -63,11 +63,9 @@ class RenderTabBar extends RenderBox with
     BoxConstraints widthConstraints =
         new BoxConstraints(maxWidth: constraints.maxWidth, maxHeight: constraints.maxHeight);
     double maxWidth = 0.0;
-    int childCount = 0;
     RenderBox child = firstChild;
     while (child != null) {
       maxWidth = math.max(maxWidth, child.getMinIntrinsicWidth(widthConstraints));
-      ++childCount;
       assert(child.parentData is TabBarParentData);
       child = child.parentData.nextSibling;
     }
@@ -78,11 +76,9 @@ class RenderTabBar extends RenderBox with
     BoxConstraints widthConstraints =
         new BoxConstraints(maxWidth: constraints.maxWidth, maxHeight: constraints.maxHeight);
     double maxWidth = 0.0;
-    int childCount = 0;
     RenderBox child = firstChild;
     while (child != null) {
       maxWidth = math.max(maxWidth, child.getMaxIntrinsicWidth(widthConstraints));
-      ++childCount;
       assert(child.parentData is TabBarParentData);
       child = child.parentData.nextSibling;
     }
@@ -95,25 +91,12 @@ class RenderTabBar extends RenderBox with
 
   double getMaxIntrinsicHeight(BoxConstraints constraints) => _getIntrinsicHeight(constraints);
 
-  // TODO(hansmuller): track this value in the parent rather than computing it.
-  int _childCount() {
-    int childCount = 0;
-    RenderBox child = firstChild;
-    while (child != null) {
-      ++childCount;
-      assert(child.parentData is TabBarParentData);
-      child = child.parentData.nextSibling;
-    }
-    return childCount;
-  }
-
   void performLayout() {
     assert(constraints is BoxConstraints);
 
     size = constraints.constrain(new Size(constraints.maxWidth, _kTabBarHeight));
     assert(!size.isInfinite);
 
-    int childCount = _childCount();
     if (childCount == 0)
       return;