Factor ScrollableList out of StockList

sky/sdk/lib/widgets/scrollable_list.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 'dart:math' as math;
+
+import 'fixed_height_scrollable.dart';
+import 'basic.dart';
+
+class ScrollableList<T> extends FixedHeightScrollable {
+  ScrollableList({
+    String key,
+    this.items,
+    this.itemBuilder,
+    double itemHeight,
+    EdgeDims padding
+  }) : super(key: key, itemHeight: itemHeight, padding: padding);
+
+  List<T> items;
+  Function itemBuilder;

[Hixie, 2015/07/07 16:49:56]

Builder, not Function.

+
+  int get itemCount => items.length;

[Hixie, 2015/07/07 16:49:56]

move itemCount below syncFields()

+
+  void syncFields(ScrollableList<T> source) {
+    items = source.items;
+    itemBuilder = source.itemBuilder;
+    super.syncFields(source);
+  }
+
+  Iterable<Widget> _buildItems(int start, int count) sync* {

[Hixie, 2015/07/07 16:49:56]

This is very fancy but I'm skeptical it's either the most readable or most
efficient way to do this. :-)

buildItems(...) {
   List<Widget> result = new List<Widget>();
   int end = math.min(start + count, items.length);
   for (int i = start; i < end; ++i)
     result.add(itemBuilder(items[i]));
   return result;
}

+    int end = math.min(start + count, items.length);
+    for (int i = start; i < end; ++i)
+      yield itemBuilder(items[i]);
+  }
+
+  List<Widget> buildItems(int start, int count) {
+    return _buildItems(start, count).toList(growable: false);

[hansmuller, 2015/07/07 17:07:12]

Doesn't apply toList() here eliminate the advantage creating an items Iterable? 

+  }
+}