Add TabNavigator

sky/sdk/lib/widgets/tabs.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 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/icon.dart';
@@ skipping 243 matching lines @@
 }
 
 class TabBar extends Component {
   TabBar({
     String key,
     this.labels,
     this.selectedIndex: 0,
     this.onChanged
   }) : super(key: key);
 
-  final List<TabLabel> labels;
+  final Iterable<TabLabel> labels;
   final int selectedIndex;
   final SelectedIndexChanged onChanged;
 
   void _handleTap(int tabIndex) {
     if (tabIndex != selectedIndex && onChanged != null)
       onChanged(tabIndex);
   }
 
   Widget _toTab(TabLabel label, int tabIndex) {
     Tab tab = new Tab(
       label: label,
       selected: tabIndex == selectedIndex,
       key: label.text == null ? label.icon : label.text
     );
     return new Listener(
       child: tab,
       onGestureTap: (_) => _handleTap(tabIndex)
     );
   }
 
   Widget build() {
     assert(labels != null && labels.isNotEmpty);
     List<Widget> tabs = <Widget>[];
     bool textAndIcons = false;
-    for (int tabIndex = 0; tabIndex < labels.length; tabIndex++) {
-      tabs.add(_toTab(labels[tabIndex], tabIndex));
-      if (labels[tabIndex].text != null && labels[tabIndex].icon != null)
+    int tabIndex = 0;
+    for (TabLabel label in labels) {
+      tabs.add(_toTab(label, tabIndex++));
+      if (label.text != null && label.icon != null)
         textAndIcons = true;
     }
     return new TabBarWrapper(
       children: tabs, 
       selectedIndex: selectedIndex,
       backgroundColor: Theme.of(this).primary[500],
       indicatorColor: Theme.of(this).accent[200],
       textAndIcons: textAndIcons
     );
   }
 }
+
+class TabNavigatorView {
+  TabNavigatorView({ this.label, this.builder });
+
+  final TabLabel label;
+  final Builder builder;
+
+  Widget buildContent() {
+    assert(builder != null);
+    Widget content = builder();
+    assert(content != null);
+    return content;
+  }
+}
+
+class TabNavigator extends Component {
+  TabNavigator({
+    String key,
+    this.views,
+    this.selectedIndex: 0,
+    this.onChanged
+  }) : super(key: key);
+
+  final List<TabNavigatorView> views;
+  final int selectedIndex;
+  final SelectedIndexChanged onChanged;
+
+  void _handleSelectedIndexChanged(int tabIndex) {
+    if (onChanged != null)
+      onChanged(tabIndex);
+  }
+
+  Widget build() {
+    assert(views != null && views.isNotEmpty);
+    assert(selectedIndex >= 0 && selectedIndex < views.length);
+
+    TabBar tabBar = new TabBar(
+      labels: views.map((view) => view.label),
+      onChanged: _handleSelectedIndexChanged,
+      selectedIndex: selectedIndex
+    );
+
+    Widget content = views[selectedIndex].buildContent();
+    return new Flex([tabBar, new Flexible(child: content)],
+      direction: FlexDirection.vertical
+    );
+  }
+}