Added button dialog and snackbar demos

examples/material_gallery/lib/demo/buttons_demo.dart

+// Copyright 2016 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 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+
+import 'tabs_fab_demo.dart';
+import 'dialog_demo.dart';
+import 'snack_bar_demo.dart';
+
+const String _floatingText =
+  "A floating action button is a circular material button that lifts "
+  "and displays an ink reaction on press. It turns and fades in when "
+  "it changes.";
+
+const String _raisedText =
+  "A raised button is typically a rectangular material button that lifts "
+  "and displays ink reactions on press. Raised buttons add dimension to "
+  "mostly flat layouts. They emphasize functions on busy or wide spaces.";
+
+const String _flatText =
+  "A flat button is made of ink that displays ink reactions on press "
+  "but does not lift. Use flat buttons on toolbars, in dialogs and "
+  "inline with padding";
+
+const String _dropdownText =
+  "A dropdown button selects between multiple selections. The button "
+  "displays the current state and a down arrow.";
+
+class _ButtonDemo {
+  _ButtonDemo({ this.title, this.text, this.builder }) {
+    assert(title != null);
+    assert(text != null);
+    assert(builder != null);
+  }
+
+  final String title;
+  final String text;
+  final WidgetBuilder builder;
+
+  TabLabel get tabLabel => new TabLabel(text: title.toUpperCase());
+
+  // The TabBarSelection created below saves and restores _ButtonDemo objects
+  // to recover this demo's selected tab. To enable it to compare restored
+  // _ButtonDemo objects with new ones, define hashCode and operator== .
+
+  bool operator==(Object other) {
+    if (other.runtimeType != runtimeType)
+      return false;
+    _ButtonDemo typedOther = other;
+    return typedOther.title == title && typedOther.text == text;
+  }
+
+  int get hashCode => hashValues(title.hashCode, text.hashCode);
+}
+
+class ButtonsDemo extends StatefulComponent {
+  _ButtonsDemoState createState() => new _ButtonsDemoState();
+}
+
+class _ButtonsDemoState extends State<ButtonsDemo> {
+  List<_ButtonDemo> demos;
+
+  void initState() {
+    super.initState();
+    demos = <_ButtonDemo>[
+      new _ButtonDemo(title: 'FLOATING', text: _floatingText, builder: buildFloatingButton),
+      new _ButtonDemo(title: 'RAISED', text: _raisedText, builder: buildRaisedButton),
+      new _ButtonDemo(title: 'FLAT', text: _flatText, builder: buildFlatButton),
+      new _ButtonDemo(title: 'DROPDOWN', text: _dropdownText, builder: buildDropdownButton)
+    ];
+  }
+
+  Widget buildFloatingButton(BuildContext context) {
+    return new SizedBox(
+      height: 128.0,
+      child: new Center(
+        child: new FloatingActionButton(
+          child: new Icon(icon: 'content/add'),
+          onPressed: () {
+            Navigator.push(context, new MaterialPageRoute(builder: (_) => new TabsFabDemo()));
+          }
+        )
+      )
+    );
+  }
+
+  Widget buildRaisedButton(BuildContext context) {
+    return new Container(
+      margin: const EdgeDims.symmetric(vertical: 16.0),
+      child: new Column(
+        children: <Widget>[
+          new RaisedButton(
+            child: new Text("Launch Demo"),
+            onPressed: () {
+              Navigator.push(context, new MaterialPageRoute(builder: (_) => new SnackBarDemo()));
+            }
+          ),
+          new RaisedButton(
+            child: new Text("Disabled")
+          )
+        ]
+        .map((Widget child) {
+          return new Container(
+            margin: const EdgeDims.symmetric(vertical: 8.0),
+            child: child
+          );
+        })
+        .toList()
+      )
+    );
+  }
+
+  Widget buildFlatButton(BuildContext context) {
+    return new Container(
+      margin: const EdgeDims.symmetric(vertical: 16.0),
+      child: new ButtonTheme(
+        color: ButtonColor.accent,
+        child: new Column(
+          children: <Widget>[
+            new FlatButton(
+              child: new Text("Launch Demo"),
+              onPressed: () {
+                showDialog(context: context, child: new DialogDemo()).then((String value) {
+                  if (value != null) {
+                    Scaffold.of(context).showSnackBar(new SnackBar(
+                      content: new Text('You dismissed the dialog with "$value"')
+                    ));
+                  }
+                });
+              }
+            ),
+            new FlatButton(
+              child: new Text("Disabled")
+            )
+          ]
+          .map((Widget child) {
+            return new Container(
+              margin: const EdgeDims.symmetric(vertical: 8.0),
+              child: child
+            );
+          })
+          .toList()
+        )
+      )
+    );
+  }
+
+  String dropdownValue = "Free";
+
+  Widget buildDropdownButton(BuildContext context) {
+    return new SizedBox(
+      height: 256.0,
+      child: new Center(
+        child: new DropDownButton<String>(
+          value: dropdownValue,
+          onChanged: (String newValue) {
+            setState(() {
+              if (newValue != null)
+                dropdownValue = newValue;
+            });
+          },
+          items: <String>["One", "Two", "Free", "Four"]
+            .map((String value) {
+              return new DropDownMenuItem<String>(
+                value: value,
+                child: new Text(value));
+            })
+            .toList()
+        )
+      )
+    );
+  }
+
+  Widget buildTabView(_ButtonDemo demo) {
+    return new Builder(
+      builder: (BuildContext context) {
+        final TextStyle textStyle = Theme.of(context).text.caption.copyWith(fontSize: 16.0);
+        return new Column(
+          alignItems: FlexAlignItems.stretch,
+          children: <Widget>[
+            demo.builder(context),
+            new Padding(
+              padding: const EdgeDims.symmetric(horizontal: 32.0),
+              child: new Text(demo.text, style: textStyle)
+            )
+          ]
+        );
+      }
+    );
+  }
+
+  Widget build(BuildContext context) {
+    return new TabBarSelection<_ButtonDemo>(
+      values: demos,
+      child: new Scaffold(
+        toolBar: new ToolBar(
+          center: new Text("Buttons"),
+          tabBar: new TabBar<_ButtonDemo>(
+            isScrollable: true,
+            labels: new Map.fromIterable(demos, value: (_ButtonDemo demo) => demo.tabLabel)
+          )
+        ),
+        body: new TabBarView(
+          children: demos.map(buildTabView).toList()
+        )
+      )
+    );
+  }
+}

examples/material_gallery/lib/demo/dialog_demo.dart

+// Copyright 2016 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 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+
+const String _dialogText =
+  "Use dialogs sparingly because they are interruptive. Their sudden appearance "
+  "forces users to stop their current task and focus on the dialog content. "
+  "Alternatives to dialogs include menus or inline expansion, both of which "
+  "maintain the current context.";
+
+class DialogDemo extends StatelessComponent {
+  DialogDemo({ Key key }) : super(key: key);
+
+  Widget build(BuildContext context) {
+    final ThemeData theme = Theme.of(context);
+    return new Dialog(
+      title: new Text("This is a Dialog"),
+      content: new Text(
+        _dialogText,
+        style: theme.text.subhead.copyWith(color: theme.text.caption.color)
+      ),
+      actions: <Widget>[
+        new FlatButton(
+          child: new Text("CANCEL"),
+          onPressed: () { Navigator.pop(context, "CANCEL"); }
+        ),
+        new FlatButton(
+          child: new Text("OK"),
+          onPressed: () { Navigator.pop(context, "OK"); }
+        )
+      ]
+    );
+  }
+}

examples/material_gallery/lib/demo/snack_bar_demo.dart

+// Copyright 2016 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 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+
+const String _text1 =
+  "Snackbars provide lightweight feedback about an operation by "
+  "showing a brief message at the bottom of the screen. Snackbars "
+  "can contain an action.";
+
+const String _text2 =
+  "Snackbars should contain a single line of text directly related "
+  "to the operation performed. They cannot contain icons.";
+
+const String _text3 =
+  "By default snackbars automatically disappear after a few seconds ";
+
+class SnackBarDemo extends StatelessComponent {
+  SnackBarDemo({ Key key }) : super(key: key);
+
+  Widget buildBody(BuildContext context) {
+    return new Padding(
+      padding: const EdgeDims.all(24.0),
+      child: new Column(
+        children: <Widget>[
+          new Text(_text1),
+          new Text(_text2),
+          new RaisedButton(
+            child: new Text('Show a SnackBar'),
+            onPressed: () {
+              Scaffold.of(context).showSnackBar(new SnackBar(
+                content: new Text('This is a SnackBar'),
+                actions: <SnackBarAction>[
+                  new SnackBarAction(
+                    label: 'Action',
+                    onPressed: () {
+                      Scaffold.of(context).showSnackBar(new SnackBar(
+                        content: new Text("You pressed the SnackBar's Action")
+                      ));
+                    }
+                  )
+                ]
+              ));
+            }
+          ),
+          new Text(_text3),
+        ]
+        .map((Widget child) {
+          return new Container(
+            margin: const EdgeDims.symmetric(vertical: 12.0),
+            child: child
+          );
+        })
+        .toList()
+      )
+    );
+  }
+
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      toolBar: new ToolBar(
+        center: new Text('SnackBar')
+      ),
+      body: new Builder(
+        // Create an inner BuildContext so that the snackBar onPressed methods
+        // can refer to the Scaffold with Scaffold.of().
+        builder: buildBody
+      )
+    );
+  }
+}

examples/material_gallery/lib/demo/tabs_demo.dart

@@ -17,7 +17,7 @@ class TabsDemo extends StatelessComponent {
             isScrollable: true,
             labels: new Map.fromIterable(
               iconNames,
-              value: (String iconName) => new TabLabel(text: iconName, icon: "action/$iconName")
+              value: (String iconName) => new TabLabel(text: iconName.toUpperCase(), icon: "action/$iconName")
             )
           )
         ),

examples/material_gallery/lib/demo/tabs_fab_demo.dart

@@ -11,7 +11,7 @@ class _Page {
   final Map<int, Color> colors;
   final String icon;
 
-  TabLabel get tabLabel => new TabLabel(text: label);
+  TabLabel get tabLabel => new TabLabel(text: label.toUpperCase());
   Color get labelColor => colors != null ? colors[300] : Colors.grey[300];
   bool get fabDefined => colors != null && icon != null;
   Color get fabColor => colors[400];
@@ -31,7 +31,7 @@ class TabsFabDemo extends StatefulComponent {
 
 class _TabsFabDemoState extends State<TabsFabDemo> {
   final GlobalKey scaffoldKey = new GlobalKey();
-  final List<_Page> _pages = <_Page>[
+  final List<_Page> pages = <_Page>[
     new _Page(label: 'Blue', colors: Colors.indigo, icon: 'content/add'),
     new _Page(label: 'Too', colors: Colors.indigo, icon: 'content/add'),
     new _Page(label: 'Eco', colors: Colors.green, icon: 'content/create'),
@@ -43,7 +43,7 @@ class _TabsFabDemoState extends State<TabsFabDemo> {
 
   void initState() {
     super.initState();
-    selectedPage = _pages[0];
+    selectedPage = pages[0];
   }
 
   void _handleTabSelection(_Page page) {
@@ -90,14 +90,14 @@ class _TabsFabDemoState extends State<TabsFabDemo> {
 
   Widget build(BuildContext context) {
     return new TabBarSelection<_Page>(
-      values: _pages,
+      values: pages,
       onChanged: _handleTabSelection,
       child: new Scaffold(
         key: scaffoldKey,
         toolBar: new ToolBar(
           center: new Text("FAB per Tab"),
           tabBar: new TabBar<_Page>(
-            labels: new Map.fromIterable(_pages, value: (_Page page) => page.tabLabel)
+            labels: new Map.fromIterable(pages, value: (_Page page) => page.tabLabel)
           )
         ),
         floatingActionButton: !selectedPage.fabDefined ? null : new FloatingActionButton(
@@ -106,7 +106,7 @@ class _TabsFabDemoState extends State<TabsFabDemo> {
           child: selectedPage.fabIcon,
           onPressed: _showExplanatoryText
         ),
-        body: new TabBarView(children: _pages.map(buildTabView).toList())
+        body: new TabBarView(children: pages.map(buildTabView).toList())
       )
     );
   }

examples/material_gallery/lib/gallery/app.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 'package:flutter/material.dart';
+
+import 'home.dart';
+
+class GalleryApp extends StatefulComponent {
+  GalleryApp({ Key key }) : super(key: key);
+
+  static GalleryAppState of(BuildContext context) => context.ancestorStateOfType(const TypeMatcher<GalleryAppState>());
+
+  GalleryAppState createState() => new GalleryAppState();
+}
+
+class GalleryAppState extends State<GalleryApp> {
+  bool _lightTheme = true;
+  bool get lightTheme => _lightTheme;
+  void set lightTheme(bool value) {
+    setState(() {
+      _lightTheme = value;
+    });
+  }
+
+  Widget build(BuildContext context) {
+    return new MaterialApp(
+      title: 'Flutter Material Gallery',
+      theme: lightTheme ? new ThemeData.light() : new ThemeData.dark(),
+      routes: {
+        '/': (RouteArguments args) => new GalleryHome()
+      }
+    );
+  }
+}

examples/material_gallery/lib/gallery/demo.dart

+// Copyright 2016 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 'package:flutter/widgets.dart';
+
+typedef Widget GalleryDemoBuilder();
+
+class GalleryDemo {
+  GalleryDemo({ this.title, this.builder }) {
+    assert(title != null);
+    assert(builder != null);
+  }
+
+  final String title;
+  final GalleryDemoBuilder builder;
+}

examples/material_gallery/lib/gallery/drawer.dart

+// Copyright 2016 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 'package:flutter/material.dart';
+import 'package:flutter/scheduler.dart' show timeDilation;
+import 'package:flutter/widgets.dart';
+
+import 'app.dart';
+
+class GalleryDrawer extends StatelessComponent {
+  GalleryDrawer({ Key key }) : super(key: key);
+
+  void _changeTheme(BuildContext context, bool value) {
+    GalleryApp.of(context).lightTheme = value;
+  }
+
+  void _toggleAnimationSpeed(BuildContext context) {
+    GalleryApp.of(context).setState(() {
+      timeDilation = (timeDilation != 1.0) ? 1.0 : 5.0;
+    });
+  }
+
+  Widget build(BuildContext context) {
+    return new Drawer(
+      child: new Block(
+        children: <Widget>[
+          new DrawerHeader(child: new Text('Flutter Gallery')),
+          new DrawerItem(
+            icon: 'image/brightness_5',
+            onPressed: () { _changeTheme(context, true); },
+            selected: GalleryApp.of(context).lightTheme,
+            child: new Row(
+              children: <Widget>[
+                new Flexible(child: new Text('Light')),
+                new Radio<bool>(
+                  value: true,
+                  groupValue: GalleryApp.of(context).lightTheme,
+                  onChanged: (bool value) { _changeTheme(context, value); }
+                )
+              ]
+            )
+          ),
+          new DrawerItem(
+            icon: 'image/brightness_7',
+            onPressed: () { _changeTheme(context, false); },
+            selected: !GalleryApp.of(context).lightTheme,
+            child: new Row(
+              children: <Widget>[
+                new Flexible(child: new Text('Dark')),
+                new Radio<bool>(
+                  value: false,
+                  groupValue: GalleryApp.of(context).lightTheme,
+                  onChanged: (bool value) { _changeTheme(context, value); }
+                )
+              ]
+            )
+          ),
+          new DrawerDivider(),
+          new DrawerItem(
+            icon: 'action/hourglass_empty',
+            selected: timeDilation != 1.0,
+            onPressed: () { _toggleAnimationSpeed(context); },
+            child: new Row(
+              children: <Widget>[
+                new Flexible(child: new Text('Animate Slowly')),
+                new Checkbox(
+                  value: timeDilation != 1.0,
+                  onChanged: (bool value) { _toggleAnimationSpeed(context); }
+                )
+              ]
+            )
+          )
+        ]
+      )
+    );
+  }
+}

examples/material_gallery/lib/gallery/home.dart

+// Copyright 2016 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 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+
+import 'demo.dart';
+import 'drawer.dart';
+import 'section.dart';
+
+import '../demo/buttons_demo.dart';
+import '../demo/chip_demo.dart';
+import '../demo/date_picker_demo.dart';
+import '../demo/dialog_demo.dart';
+import '../demo/drop_down_demo.dart';
+import '../demo/modal_bottom_sheet_demo.dart';
+import '../demo/page_selector_demo.dart';
+import '../demo/persistent_bottom_sheet_demo.dart';
+import '../demo/progress_indicator_demo.dart';
+import '../demo/toggle_controls_demo.dart';
+import '../demo/scrolling_techniques_demo.dart';
+import '../demo/slider_demo.dart';
+import '../demo/snack_bar_demo.dart';
+import '../demo/tabs_demo.dart';
+import '../demo/tabs_fab_demo.dart';
+import '../demo/time_picker_demo.dart';
+import '../demo/two_level_list_demo.dart';
+import '../demo/weathers_demo.dart';
+
+class GalleryHome extends StatefulComponent {
+  GalleryHome({ Key key }) : super(key: key);
+
+  GalleryHomeState createState() => new GalleryHomeState();
+}
+
+class GalleryHomeState extends State<GalleryHome> {
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      appBarHeight: 128.0,
+      drawer: new GalleryDrawer(),
+      toolBar: new ToolBar(
+        flexibleSpace: (BuildContext context) {
+          return new Container(
+            padding: const EdgeDims.only(left: 16.0, bottom: 24.0),
+            height: 128.0,
+            child: new Align(
+              alignment: const FractionalOffset(0.0, 1.0),
+              child: new Text('Flutter Gallery', style: Typography.white.headline)
+            )
+          );
+        }
+      ),
+      body: new Padding(
+        padding: const EdgeDims.all(4.0),
+        child: new Block(
+          children: <Widget>[
+            new Row(
+              children: <Widget>[
+                new GallerySection(
+                  title: 'Animation',
+                  image: 'assets/section_animation.png',
+                  colors: Colors.purple,
+                  demos: <GalleryDemo>[
+                    new GalleryDemo(title: 'Weathers', builder: () => new WeathersDemo())
+                  ]
+                ),
+                new GallerySection(
+                  title: 'Style',
+                  image: 'assets/section_style.png',
+                  colors: Colors.green
+                )
+              ]
+            ),
+            new Row(
+              children: <Widget>[
+                new GallerySection(
+                  title: 'Layout',
+                  image: 'assets/section_layout.png',
+                  colors: Colors.pink
+                ),
+                new GallerySection(
+                  title: 'Components',
+                  image: 'assets/section_components.png',
+                  colors: Colors.amber,
+                  demos: <GalleryDemo>[
+                    new GalleryDemo(title: 'Buttons', builder: () => new ButtonsDemo()),
+                    new GalleryDemo(title: 'Chips', builder: () => new ChipDemo()),
+                    new GalleryDemo(title: 'Date Picker', builder: () => new DatePickerDemo()),
+                    new GalleryDemo(title: 'Dialog', builder: () => new DialogDemo()),
+                    new GalleryDemo(title: 'Dropdown Button', builder: () => new DropDownDemo()),
+                    new GalleryDemo(title: 'Expland/Collapse List Control', builder: () => new TwoLevelListDemo()),
+                    new GalleryDemo(title: 'Floating Action Button', builder: () => new TabsFabDemo()),
+                    new GalleryDemo(title: 'Modal Bottom Sheet', builder: () => new ModalBottomSheetDemo()),
+                    new GalleryDemo(title: 'Page Selector', builder: () => new PageSelectorDemo()),
+                    new GalleryDemo(title: 'Persistent Bottom Sheet', builder: () => new PersistentBottomSheetDemo()),
+                    new GalleryDemo(title: 'Progress Indicators', builder: () => new ProgressIndicatorDemo()),
+                    new GalleryDemo(title: 'Selection Controls', builder: () => new ToggleControlsDemo()),
+                    new GalleryDemo(title: 'Sliders', builder: () => new SliderDemo()),
+                    new GalleryDemo(title: 'SnackBar', builder: () => new SnackBarDemo()),
+                    new GalleryDemo(title: 'Tabs', builder: () => new TabsDemo()),
+                    new GalleryDemo(title: 'Time Picker', builder: () => new TimePickerDemo())
+                  ]
+                )
+              ]
+            ),
+            new Row(
+              children: <Widget>[
+                new GallerySection(
+                  title: 'Patterns',
+                  image: 'assets/section_patterns.png',
+                  colors: Colors.cyan,
+                  demos: <GalleryDemo>[
+                    new GalleryDemo(title: 'Scrolling Techniques', builder: () => new ScrollingTechniquesDemo())
+                  ]
+                ),
+                new GallerySection(
+                  title: 'Usability',
+                  image: 'assets/section_usability.png',
+                  colors: Colors.lightGreen
+                )
+              ]
+            )
+          ]
+        )
+      )
+    );
+  }
+}

examples/material_gallery/lib/gallery/section.dart

+// Copyright 2016 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 'package:flutter/material.dart';
+import 'package:flutter/widgets.dart';
+
+import 'demo.dart';
+
+class GallerySection extends StatelessComponent {
+  GallerySection({ this.title, this.image, this.colors, this.demos });
+
+  final String title;
+  final String image;
+  final Map<int, Color> colors;
+  final List<GalleryDemo> demos;
+
+  void showDemo(GalleryDemo demo, BuildContext context, ThemeData theme) {
+    Navigator.push(context, new MaterialPageRoute(
+      builder: (BuildContext context) {
+        Widget child = (demo.builder == null) ? null : demo.builder();
+        return new Theme(data: theme, child: child);
+      }
+    ));
+  }
+
+  void showDemos(BuildContext context) {
+    final ThemeData theme = new ThemeData(
+      brightness: Theme.of(context).brightness,
+      primarySwatch: colors
+    );
+    final double appBarHeight = 200.0;
+    final Key scrollableKey = new ValueKey<String>(title); // assume section titles differ
+    Navigator.push(context, new MaterialPageRoute(
+      builder: (BuildContext context) {
+        return new Theme(
+          data: theme,
+          child: new Scaffold(
+            appBarHeight: appBarHeight,
+            appBarBehavior: AppBarBehavior.scroll,
+            scrollableKey: scrollableKey,
+            toolBar: new ToolBar(
+              flexibleSpace: (BuildContext context) => new FlexibleSpaceBar(title: new Text(title))
+            ),
+            body: new Material(
+              child: new MaterialList(
+                scrollableKey: scrollableKey,
+                scrollablePadding: new EdgeDims.only(top: appBarHeight),
+                type: MaterialListType.oneLine,
+                children: (demos ?? const <GalleryDemo>[]).map((GalleryDemo demo) {
+                  return new ListItem(
+                    center: new Text(demo.title, style: theme.text.subhead),
+                    onTap: () { showDemo(demo, context, theme); }
+                  );
+                })
+              )
+            )
+          )
+        );
+      }
+    ));
+  }
+
+  Widget build (BuildContext context) {
+    final ThemeData theme = new ThemeData(
+      brightness: Theme.of(context).brightness,
+      primarySwatch: colors
+    );
+    final TextStyle titleTextStyle = theme.text.title.copyWith(
+      color: theme.brightness == ThemeBrightness.dark ?  Colors.black : Colors.white
+    );
+    return new Flexible(
+      child: new GestureDetector(
+        behavior: HitTestBehavior.opaque,
+        onTap: () { showDemos(context); },
+        child: new Container(
+          height: 256.0,
+          margin: const EdgeDims.all(4.0),
+          decoration: new BoxDecoration(backgroundColor: theme.primaryColor),
+          child: new Column(
+            children: <Widget>[
+              new Flexible(
+                child: new Padding(
+                  padding: const EdgeDims.symmetric(horizontal: 12.0),
+                  child: new AssetImage(
+                    name: image,
+                    alignment: const FractionalOffset(0.5, 0.5),
+                    fit: ImageFit.contain
+                  )
+                )
+              ),
+              new Padding(
+                padding: const EdgeDims.all(16.0),
+                child: new Align(
+                  alignment: const FractionalOffset(0.0, 1.0),
+                  child: new Text(title, style: titleTextStyle)
+                )
+              )
+            ]
+          )
+        )
+      )
+    );
+  }
+}

packages/flutter/lib/src/material/material_button.dart

@@ -134,7 +134,8 @@ abstract class MaterialButtonState<T extends MaterialButton> extends State<T> {
     return new Container(
       height: 36.0,
       constraints: new BoxConstraints(minWidth: 88.0),
-      margin: new EdgeDims.all(8.0),
+      padding: const EdgeDims.symmetric(horizontal: 8.0),
+      margin: const EdgeDims.all(8.0),
       child: contents
     );
   }

packages/flutter/lib/src/material/tabs.dart

@@ -436,6 +436,12 @@ class TabBarSelectionState<T> extends State<TabBarSelection<T>> {
   void initState() {
     super.initState();
     _value = config.value ?? PageStorage.of(context)?.readState(context) ?? values.first;
+
+    // If the selection's values have changed since the selected value was saved with
+    // PageStorage.writeState() then use the default.
+    if (!values.contains(_value))
+      _value = values.first;
+
     _previousValue = _value;
     _initValueToIndex();
   }
@@ -870,6 +876,7 @@ class _TabBarViewState extends PageableListState<TabBarView> implements TabBarSe
   void _updateItemsAndScrollBehavior() {
     assert(_selection != null);
     final int selectedIndex = _selection.index;
+    assert(selectedIndex != null);
     _updateItemsForSelectedIndex(selectedIndex);
     _updateScrollBehaviorForSelectedIndex(selectedIndex);
   }