Load stocks data off the network

sky/framework/components/fixed_height_scrollable.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import '../animation/scroll_behavior.dart';
 import '../fn.dart';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
+import 'dart:async';
 import 'scrollable.dart';
 
 abstract class FixedHeightScrollable extends Scrollable {
   static final Style _style = new Style('''
     overflow: hidden;
     position: relative;
     will-change: transform;'''
   );
 
   static final Style _scrollAreaStyle = new Style('''
     position:relative;
     will-change: transform;'''
   );
 
   double _height = 0.0;
   double _itemHeight;
 
   FixedHeightScrollable({
     Object key,
     ScrollBehavior scrollBehavior
-  }) : super(key: key, scrollBehavior: scrollBehavior) {
-    onDidMount(_measureHeights);
-  }
+  }) : super(key: key, scrollBehavior: scrollBehavior);
 
   void _measureHeights() {
+    if (_itemHeight != null)
+      return;
     var root = getRoot();
+    if (root == null)
+      return;
     var item = root.firstChild.firstChild;
+    if (item == null)
+      return;
     sky.ClientRect scrollRect = root.getBoundingClientRect();
     sky.ClientRect itemRect = item.getBoundingClientRect();
     assert(scrollRect.height > 0);
     assert(itemRect.height > 0);
 
     setState(() {
       _height = scrollRect.height;
       _itemHeight = itemRect.height;
     });
   }
 
   Node buildContent() {
     var itemNumber = 0;
     var drawCount = 1;
     var transformStyle = '';
 
-    if (_height > 0.0) {
+    if (_itemHeight == null)
+      new Future.microtask(_measureHeights);
+
+    if (_height > 0.0 && _itemHeight != null) {
       if (scrollOffset < 0.0) {
         double visibleHeight = _height + scrollOffset;
         drawCount = (visibleHeight / _itemHeight).round() + 1;
         transformStyle =
           'transform: translateY(${(-scrollOffset).toStringAsFixed(2)}px)';
       } else {
         drawCount = (_height / _itemHeight).round() + 1;
         double alignmentOffset = math.max(0.0, scrollOffset);
         double alignmentDelta = -scrollOffset % _itemHeight;
         if (alignmentDelta != 0.0)
@@ skipping 12 matching lines @@
       children: [
         new Container(
           style: _scrollAreaStyle,
           inlineStyle: transformStyle,
           children: buildItems(itemNumber, drawCount)
         )
       ]
     );
   }
 }