Add API docs link to each gallery demo (#22379)

examples/flutter_gallery/lib/demo/cupertino/cupertino_activity_indicator_demo.dart

@@ -3,18 +3,21 @@
 // found in the LICENSE file.
 
 import 'package:flutter/cupertino.dart';
-import 'package:flutter/material.dart';
+
+import '../../gallery/demo.dart';
 
 class CupertinoProgressIndicatorDemo extends StatelessWidget {
   static const String routeName = '/cupertino/progress_indicator';
 
   @override
   Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(
-        title: const Text('Cupertino Activity Indicator'),
+    return CupertinoPageScaffold(
+      navigationBar: CupertinoNavigationBar(
+        previousPageTitle: 'Cupertino',
+        middle: const Text('Cupertino Activity Indicator'),
+        trailing: CupertinoDemoDocumentationButton(routeName),
       ),
-      body: const Center(
+      child: const Center(
         child: CupertinoActivityIndicator(),
       ),
     );

examples/flutter_gallery/lib/demo/cupertino/cupertino_alert_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class CupertinoAlertDemo extends StatefulWidget {
   static const String routeName = '/cupertino/alert';
 
@@ -53,6 +55,7 @@ class _CupertinoAlertDemoState extends State<CupertinoAlertDemo> {
       key: _scaffoldKey,
       appBar: AppBar(
         title: const Text('Cupertino Alerts'),
+        actions: <Widget>[MaterialDemoDocumentationButton(CupertinoAlertDemo.routeName)],
       ),
       body: ListView(
         padding: const EdgeInsets.symmetric(vertical: 24.0, horizontal: 72.0),

examples/flutter_gallery/lib/demo/cupertino/cupertino_buttons_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class CupertinoButtonsDemo extends StatefulWidget {
   static const String routeName = '/cupertino/buttons';
 
@@ -20,6 +22,7 @@ class _CupertinoButtonDemoState extends State<CupertinoButtonsDemo> {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Cupertino Buttons'),
+        actions: <Widget>[MaterialDemoDocumentationButton(CupertinoButtonsDemo.routeName)],
       ),
       body: Column(
         children: <Widget> [

examples/flutter_gallery/lib/demo/cupertino/cupertino_navigation_demo.dart

@@ -8,6 +8,8 @@ import 'dart:math' as math;
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const String _kGalleryAssetsPackage = 'flutter_gallery_assets';
 
 const List<Color> coolColors = <Color>[
@@ -125,6 +127,15 @@ class ExitButton extends StatelessWidget {
   }
 }
 
+final Widget trailingButtons = Row(
+  mainAxisSize: MainAxisSize.min,
+  children: <Widget>[
+    CupertinoDemoDocumentationButton(CupertinoNavigationDemo.routeName),
+    const Padding(padding: EdgeInsets.only(left: 8.0)),
+    const ExitButton(),
+  ],
+);
+
 class CupertinoDemoTab1 extends StatelessWidget {
   const CupertinoDemoTab1({this.colorItems, this.colorNameItems});
 
@@ -136,8 +147,8 @@ class CupertinoDemoTab1 extends StatelessWidget {
     return CupertinoPageScaffold(
       child: CustomScrollView(
         slivers: <Widget>[
-          const CupertinoSliverNavigationBar(
-            trailing: ExitButton(),
+          CupertinoSliverNavigationBar(
+            trailing: trailingButtons,
           ),
           SliverPadding(
             // Top media padding consumed by CupertinoSliverNavigationBar.
@@ -421,8 +432,8 @@ class CupertinoDemoTab2 extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return CupertinoPageScaffold(
-      navigationBar: const CupertinoNavigationBar(
-        trailing: ExitButton(),
+      navigationBar: CupertinoNavigationBar(
+        trailing: trailingButtons,
       ),
       child: ListView(
         children: <Widget>[
@@ -704,8 +715,8 @@ class CupertinoDemoTab3 extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return CupertinoPageScaffold(
-      navigationBar: const CupertinoNavigationBar(
-        trailing: ExitButton(),
+      navigationBar: CupertinoNavigationBar(
+        trailing: trailingButtons,
       ),
       child: DecoratedBox(
         decoration: const BoxDecoration(color: Color(0xFFEFEFF4)),

examples/flutter_gallery/lib/demo/cupertino/cupertino_picker_demo.dart

@@ -4,6 +4,7 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
 import 'cupertino_navigation_demo.dart' show coolColorNames;
 
 const double _kPickerSheetHeight = 216.0;
@@ -132,6 +133,7 @@ class _CupertinoPickerDemoState extends State<CupertinoPickerDemo> {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Cupertino Picker'),
+        actions: <Widget>[MaterialDemoDocumentationButton(CupertinoPickerDemo.routeName)],
       ),
       body: DefaultTextStyle(
         style: const TextStyle(

examples/flutter_gallery/lib/demo/cupertino/cupertino_refresh_demo.dart

@@ -6,6 +6,8 @@ import 'dart:math' show Random;
 
 import 'package:flutter/cupertino.dart';
 
+import '../../gallery/demo.dart';
+
 class CupertinoRefreshControlDemo extends StatefulWidget {
   static const String routeName = '/cupertino/refresh';
 
@@ -48,9 +50,10 @@ class _CupertinoRefreshControlDemoState extends State<CupertinoRefreshControlDem
           decoration: const BoxDecoration(color: Color(0xFFEFEFF4)),
           child: CustomScrollView(
             slivers: <Widget>[
-              const CupertinoSliverNavigationBar(
-                largeTitle: Text('Cupertino Refresh'),
+              CupertinoSliverNavigationBar(
+                largeTitle: const Text('Cupertino Refresh'),
                 previousPageTitle: 'Cupertino',
+                trailing: CupertinoDemoDocumentationButton(CupertinoRefreshControlDemo.routeName),
               ),
               CupertinoSliverRefreshControl(
                 onRefresh: () {

examples/flutter_gallery/lib/demo/cupertino/cupertino_segmented_control_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const Color _kKeyUmbraOpacity = Color(0x33000000); // alpha = 0.2
 const Color _kKeyPenumbraOpacity = Color(0x24000000); // alpha = 0.14
 const Color _kAmbientShadowOpacity = Color(0x1F000000); // alpha = 0.12
@@ -51,6 +53,7 @@ class _CupertinoSegmentedControlDemoState extends State<CupertinoSegmentedContro
     return Scaffold(
       appBar: AppBar(
         title: const Text('Segmented Control'),
+        actions: <Widget>[MaterialDemoDocumentationButton(CupertinoSegmentedControlDemo.routeName)],
       ),
       body: Column(
         children: <Widget>[

examples/flutter_gallery/lib/demo/cupertino/cupertino_slider_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class CupertinoSliderDemo extends StatefulWidget {
   static const String routeName = '/cupertino/slider';
 
@@ -21,6 +23,7 @@ class _CupertinoSliderDemoState extends State<CupertinoSliderDemo> {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Cupertino Sliders'),
+        actions: <Widget>[MaterialDemoDocumentationButton(CupertinoSliderDemo.routeName)],
       ),
       body: Center(
         child: Column(

examples/flutter_gallery/lib/demo/cupertino/cupertino_switch_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class CupertinoSwitchDemo extends StatefulWidget {
   static const String routeName = '/cupertino/switch';
 
@@ -21,6 +23,7 @@ class _CupertinoSwitchDemoState extends State<CupertinoSwitchDemo> {
     return Scaffold(
       appBar: AppBar(
         title: const Text('Cupertino Switch'),
+        actions: <Widget>[MaterialDemoDocumentationButton(CupertinoSwitchDemo.routeName)],
       ),
       body: Center(
         child: Column(

examples/flutter_gallery/lib/demo/material/bottom_app_bar_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class BottomAppBarDemo extends StatefulWidget {
   static const String routeName = '/material/bottom_app_bar';
 
@@ -143,6 +145,7 @@ class _BottomAppBarDemoState extends State<BottomAppBarDemo> {
         title: const Text('Bottom app bar'),
         elevation: 0.0,
         actions: <Widget>[
+          MaterialDemoDocumentationButton(BottomAppBarDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sentiment_very_satisfied),
             onPressed: () {

examples/flutter_gallery/lib/demo/material/bottom_navigation_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class NavigationIconView {
   NavigationIconView({
     Widget icon,
@@ -209,6 +211,7 @@ class _BottomNavigationDemoState extends State<BottomNavigationDemo>
       appBar: AppBar(
         title: const Text('Bottom navigation'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(BottomNavigationDemo.routeName),
           PopupMenuButton<BottomNavigationBarType>(
             onSelected: (BottomNavigationBarType value) {
               setState(() {

examples/flutter_gallery/lib/demo/material/buttons_demo.dart

@@ -70,6 +70,7 @@ class _ButtonsDemoState extends State<ButtonsDemo> {
           child: buildRaisedButton(),
         ),
         exampleCodeTag: _raisedCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/RaisedButton-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'FLAT',
@@ -79,6 +80,7 @@ class _ButtonsDemoState extends State<ButtonsDemo> {
           child: buildFlatButton(),
         ),
         exampleCodeTag: _flatCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/FlatButton-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'OUTLINE',
@@ -88,24 +90,28 @@ class _ButtonsDemoState extends State<ButtonsDemo> {
           child: buildOutlineButton(),
         ),
         exampleCodeTag: _outlineCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/OutlineButton-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'DROPDOWN',
         description: _dropdownText,
         demoWidget: buildDropdownButton(),
         exampleCodeTag: _dropdownCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/DropdownButton-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'ICON',
         description: _iconText,
         demoWidget: buildIconButton(),
         exampleCodeTag: _iconCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/IconButton-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'ACTION',
         description: _actionText,
         demoWidget: buildActionButton(),
         exampleCodeTag: _actionCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/FloatingActionButton-class.html',
       ),
     ];
 

examples/flutter_gallery/lib/demo/material/cards_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const String _kGalleryAssetsPackage = 'flutter_gallery_assets';
 
 class TravelDestination {
@@ -168,6 +170,7 @@ class _CardsDemoState extends State<CardsDemo> {
       appBar: AppBar(
         title: const Text('Travel stream'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(CardsDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sentiment_very_satisfied),
             onPressed: () {

examples/flutter_gallery/lib/demo/material/chip_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const List<String> _defaultMaterials = <String>[
   'poker',
   'tortilla',
@@ -303,6 +305,7 @@ class _ChipDemoState extends State<ChipDemo> {
       appBar: AppBar(
         title: const Text('Chips'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(ChipDemo.routeName),
           IconButton(
             onPressed: () {
               setState(() {

examples/flutter_gallery/lib/demo/material/data_table_demo.dart

@@ -5,6 +5,8 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
+import '../../gallery/demo.dart';
+
 class Dessert {
   Dessert(this.name, this.calories, this.fat, this.carbs, this.protein, this.sodium, this.calcium, this.iron);
   final String name;
@@ -164,7 +166,12 @@ class _DataTableDemoState extends State<DataTableDemo> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Data tables')),
+      appBar: AppBar(
+        title: const Text('Data tables'),
+        actions: <Widget>[
+          MaterialDemoDocumentationButton(DataTableDemo.routeName),
+        ],
+      ),
       body: ListView(
         padding: const EdgeInsets.all(20.0),
         children: <Widget>[

examples/flutter_gallery/lib/demo/material/date_and_time_picker_demo.dart

@@ -7,6 +7,8 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart';
 
+import '../../gallery/demo.dart';
+
 class _InputDropdown extends StatelessWidget {
   const _InputDropdown({
     Key key,
@@ -129,7 +131,10 @@ class _DateAndTimePickerDemoState extends State<DateAndTimePickerDemo> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Date and time pickers')),
+      appBar: AppBar(
+        title: const Text('Date and time pickers'),
+        actions: <Widget>[MaterialDemoDocumentationButton(DateAndTimePickerDemo.routeName)],
+      ),
       body: DropdownButtonHideUnderline(
         child: SafeArea(
           top: false,

examples/flutter_gallery/lib/demo/material/dialog_demo.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
 import 'full_screen_dialog_demo.dart';
 
 enum DialogDemoAction {
@@ -87,7 +88,8 @@ class DialogDemoState extends State<DialogDemo> {
     return Scaffold(
       key: _scaffoldKey,
       appBar: AppBar(
-        title: const Text('Dialogs')
+        title: const Text('Dialogs'),
+        actions: <Widget>[MaterialDemoDocumentationButton(DialogDemo.routeName)],
       ),
       body: ListView(
         padding: const EdgeInsets.symmetric(vertical: 24.0, horizontal: 72.0),

examples/flutter_gallery/lib/demo/material/drawer_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const String _kAsset0 = 'people/square/trevor.png';
 const String _kAsset1 = 'people/square/stella.png';
 const String _kAsset2 = 'people/square/sandra.png';
@@ -88,6 +90,7 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
           },
         ),
         title: const Text('Navigation drawer'),
+        actions: <Widget>[MaterialDemoDocumentationButton(DrawerDemo.routeName)],
       ),
       drawer: Drawer(
         child: Column(

examples/flutter_gallery/lib/demo/material/elevation_demo.dart

 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class ElevationDemo extends StatefulWidget {
   static const String routeName = '/material/elevation';
 
@@ -46,6 +48,7 @@ class _ElevationDemoState extends State<ElevationDemo> {
       appBar: AppBar(
         title: const Text('Elevation'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(ElevationDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sentiment_very_satisfied),
             onPressed: () {

examples/flutter_gallery/lib/demo/material/expansion_panels_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 enum _Location {
   Barbados,
   Bahamas,
@@ -336,7 +338,12 @@ class _ExpansionPanelsDemoState extends State<ExpansionPanelsDemo> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Expansion panels')),
+      appBar: AppBar(
+        title: const Text('Expansion panels'),
+        actions: <Widget>[
+          MaterialDemoDocumentationButton(ExpansionPanelsDemo.routeName),
+        ],
+      ),
       body: SingleChildScrollView(
         child: SafeArea(
           top: false,

examples/flutter_gallery/lib/demo/material/grid_list_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 enum GridDemoTileStyle {
   imageOnly,
   oneLine,
@@ -340,6 +342,7 @@ class GridListDemoState extends State<GridListDemo> {
       appBar: AppBar(
         title: const Text('Grid list'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(GridListDemo.routeName),
           PopupMenuButton<GridDemoTileStyle>(
             onSelected: changeTileStyle,
             itemBuilder: (BuildContext context) => <PopupMenuItem<GridDemoTileStyle>>[

examples/flutter_gallery/lib/demo/material/icons_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class IconsDemo extends StatefulWidget {
   static const String routeName = '/material/icons';
 
@@ -48,7 +50,8 @@ class IconsDemoState extends State<IconsDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: const Text('Icons')
+        title: const Text('Icons'),
+        actions: <Widget>[MaterialDemoDocumentationButton(IconsDemo.routeName)],
       ),
       body: IconTheme(
         data: IconThemeData(color: iconColor),

examples/flutter_gallery/lib/demo/material/leave_behind_demo.dart

@@ -7,6 +7,8 @@ import 'package:collection/collection.dart' show lowerBound;
 import 'package:flutter/material.dart';
 import 'package:flutter/semantics.dart';
 
+import '../../gallery/demo.dart';
+
 enum LeaveBehindDemoAction {
   reset,
   horizontalSwipe,
@@ -140,6 +142,7 @@ class LeaveBehindDemoState extends State<LeaveBehindDemo> {
       appBar: AppBar(
         title: const Text('Swipe to dismiss'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(LeaveBehindDemo.routeName),
           PopupMenuButton<LeaveBehindDemoAction>(
             onSelected: handleDemoAction,
             itemBuilder: (BuildContext context) => <PopupMenuEntry<LeaveBehindDemoAction>>[

examples/flutter_gallery/lib/demo/material/list_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 enum _MaterialListType {
   /// A list tile that contains a single line of text.
   oneLine,
@@ -216,6 +218,7 @@ class _ListDemoState extends State<ListDemo> {
       appBar: AppBar(
         title: Text('Scrolling list\n$itemTypeText$layoutText'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(ListDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sort_by_alpha),
             tooltip: 'Sort',

examples/flutter_gallery/lib/demo/material/menu_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class MenuDemo extends StatefulWidget {
   const MenuDemo({ Key key }) : super(key: key);
 
@@ -64,6 +66,7 @@ class MenuDemoState extends State<MenuDemo> {
       appBar: AppBar(
         title: const Text('Menus'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(MenuDemo.routeName),
           PopupMenuButton<String>(
             onSelected: showMenuSelection,
             itemBuilder: (BuildContext context) => <PopupMenuItem<String>>[

examples/flutter_gallery/lib/demo/material/modal_bottom_sheet_demo.dart

@@ -4,13 +4,18 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class ModalBottomSheetDemo extends StatelessWidget {
   static const String routeName = '/material/modal-bottom-sheet';
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Modal bottom sheet')),
+      appBar: AppBar(
+        title: const Text('Modal bottom sheet'),
+        actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
+      ),
       body: Center(
         child: RaisedButton(
           child: const Text('SHOW BOTTOM SHEET'),

examples/flutter_gallery/lib/demo/material/overscroll_demo.dart

@@ -6,6 +6,8 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 enum IndicatorType { overscroll, refresh }
 
 class OverscrollDemo extends StatefulWidget {
@@ -47,6 +49,7 @@ class OverscrollDemoState extends State<OverscrollDemo> {
       appBar: AppBar(
         title: const Text('Pull to refresh'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(OverscrollDemo.routeName),
           IconButton(
             icon: const Icon(Icons.refresh),
             tooltip: 'Refresh',

examples/flutter_gallery/lib/demo/material/page_selector_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class _PageSelector extends StatelessWidget {
   const _PageSelector({ this.icons });
 
@@ -85,7 +87,10 @@ class PageSelectorDemo extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Page selector')),
+      appBar: AppBar(
+        title: const Text('Page selector'),
+        actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
+      ),
       body: DefaultTabController(
         length: icons.length,
         child: _PageSelector(icons: icons),

examples/flutter_gallery/lib/demo/material/persistent_bottom_sheet_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class PersistentBottomSheetDemo extends StatefulWidget {
   static const String routeName = '/material/persistent-bottom-sheet';
 
@@ -76,7 +78,12 @@ class _PersistentBottomSheetDemoState extends State<PersistentBottomSheetDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       key: _scaffoldKey,
-      appBar: AppBar(title: const Text('Persistent bottom sheet')),
+      appBar: AppBar(
+        title: const Text('Persistent bottom sheet'),
+        actions: <Widget>[
+          MaterialDemoDocumentationButton(PersistentBottomSheetDemo.routeName),
+        ],
+      ),
       floatingActionButton: FloatingActionButton(
         onPressed: _showMessage,
         backgroundColor: Colors.redAccent,

examples/flutter_gallery/lib/demo/material/progress_indicator_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class ProgressIndicatorDemo extends StatefulWidget {
   static const String routeName = '/material/progress-indicator';
 
@@ -100,7 +102,10 @@ class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo> with Sing
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Progress indicators')),
+      appBar: AppBar(
+        title: const Text('Progress indicators'),
+        actions: <Widget>[MaterialDemoDocumentationButton(ProgressIndicatorDemo.routeName)],
+      ),
       body: Center(
         child: SingleChildScrollView(
           child: DefaultTextStyle(

examples/flutter_gallery/lib/demo/material/reorderable_list_demo.dart

@@ -6,6 +6,8 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
+import '../../gallery/demo.dart';
+
 enum _ReorderableListType {
   /// A list tile that contains a [CircleAvatar].
   horizontalAvatar,
@@ -157,6 +159,7 @@ class _ListDemoState extends State<ReorderableListDemo> {
       appBar: AppBar(
         title: const Text('Reorderable list'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(ReorderableListDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sort_by_alpha),
             tooltip: 'Sort',

examples/flutter_gallery/lib/demo/material/scrollable_tabs_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 enum TabsDemoStyle {
   iconsAndText,
   iconsOnly,
@@ -125,6 +127,7 @@ class ScrollableTabsDemoState extends State<ScrollableTabsDemo> with SingleTicke
       appBar: AppBar(
         title: const Text('Scrollable tabs'),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(ScrollableTabsDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sentiment_very_satisfied),
             onPressed: () {

examples/flutter_gallery/lib/demo/material/search_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class SearchDemo extends StatefulWidget {
   static const String routeName = '/material/search';
 
@@ -50,6 +52,7 @@ class _SearchDemoState extends State<SearchDemo> {
               }
             },
           ),
+          MaterialDemoDocumentationButton(SearchDemo.routeName),
           IconButton(
             tooltip: 'More (not implemented)',
             icon: Icon(

examples/flutter_gallery/lib/demo/material/selection_controls_demo.dart

@@ -42,19 +42,22 @@ class _SelectionControlsDemoState extends State<SelectionControlsDemo> {
         tabName: 'CHECKBOX',
         description: _checkboxText,
         demoWidget: buildCheckbox(),
-        exampleCodeTag: _checkboxCode
+        exampleCodeTag: _checkboxCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/Checkbox-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'RADIO',
         description: _radioText,
         demoWidget: buildRadio(),
-        exampleCodeTag: _radioCode
+        exampleCodeTag: _radioCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/Radio-class.html',
       ),
       ComponentDemoTabData(
         tabName: 'SWITCH',
         description: _switchText,
         demoWidget: buildSwitch(),
-        exampleCodeTag: _switchCode
+        exampleCodeTag: _switchCode,
+        documentationUrl: 'https://docs.flutter.io/flutter/material/Switch-class.html',
       )
     ];
 

examples/flutter_gallery/lib/demo/material/slider_demo.dart

@@ -6,6 +6,8 @@ import 'dart:math' as math;
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class SliderDemo extends StatefulWidget {
   static const String routeName = '/material/slider';
 
@@ -132,7 +134,10 @@ class _SliderDemoState extends State<SliderDemo> {
   Widget build(BuildContext context) {
     final ThemeData theme = Theme.of(context);
     return Scaffold(
-      appBar: AppBar(title: const Text('Sliders')),
+      appBar: AppBar(
+        title: const Text('Sliders'),
+        actions: <Widget>[MaterialDemoDocumentationButton(SliderDemo.routeName)],
+      ),
       body: Padding(
         padding: const EdgeInsets.symmetric(horizontal: 40.0),
         child: Column(

examples/flutter_gallery/lib/demo/material/snack_bar_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const String _text1 =
   'Snackbars provide lightweight feedback about an operation by '
   'showing a brief message at the bottom of the screen. Snackbars '
@@ -73,7 +75,8 @@ class _SnackBarDemoState extends State<SnackBarDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: const Text('Snackbar')
+        title: const Text('Snackbar'),
+        actions: <Widget>[MaterialDemoDocumentationButton(SnackBarDemo.routeName)],
       ),
       body: Builder(
         // Create an inner BuildContext so that the snackBar onPressed methods

examples/flutter_gallery/lib/demo/material/tabs_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 // Each TabBarView contains a _Page and for each _Page there is a list
 // of _CardData objects. Each _CardData object is displayed by a _CardItem.
 
@@ -150,6 +152,7 @@ class TabsDemo extends StatelessWidget {
                 handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                 child: SliverAppBar(
                   title: const Text('Tabs and scrolling'),
+                  actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
                   pinned: true,
                   expandedHeight: 150.0,
                   forceElevated: innerBoxIsScrolled,

examples/flutter_gallery/lib/demo/material/tabs_fab_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const String _explanatoryText =
   "When the Scaffold's floating action button changes, the new button fades and "
   'turns into view. In this demo, changing tabs can cause the app to be rebuilt '
@@ -137,6 +139,7 @@ class _TabsFabDemoState extends State<TabsFabDemo> with SingleTickerProviderStat
           tabs: _allPages.map((_Page page) => Tab(text: page.label.toUpperCase())).toList(),
         ),
         actions: <Widget>[
+          MaterialDemoDocumentationButton(TabsFabDemo.routeName),
           IconButton(
             icon: const Icon(Icons.sentiment_very_satisfied),
             onPressed: () {

examples/flutter_gallery/lib/demo/material/text_form_field_demo.dart

@@ -7,6 +7,8 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
+import '../../gallery/demo.dart';
+
 class TextFormFieldDemo extends StatefulWidget {
   const TextFormFieldDemo({ Key key }) : super(key: key);
 
@@ -165,6 +167,7 @@ class TextFormFieldDemoState extends State<TextFormFieldDemo> {
       key: _scaffoldKey,
       appBar: AppBar(
         title: const Text('Text fields'),
+        actions: <Widget>[MaterialDemoDocumentationButton(TextFormFieldDemo.routeName)],
       ),
       body: SafeArea(
         top: false,

examples/flutter_gallery/lib/demo/material/tooltip_demo.dart

@@ -4,6 +4,8 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 const String _introText =
   'Tooltips are short identifying messages that briefly appear in response to '
   'a long press. Tooltip messages are also used by services that make Flutter '
@@ -18,7 +20,8 @@ class TooltipDemo extends StatelessWidget {
     final ThemeData theme = Theme.of(context);
     return Scaffold(
       appBar: AppBar(
-        title: const Text('Tooltips')
+        title: const Text('Tooltips'),
+        actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
       ),
       body: Builder(
         builder: (BuildContext context) {

examples/flutter_gallery/lib/demo/material/two_level_list_demo.dart

@@ -4,13 +4,18 @@
 
 import 'package:flutter/material.dart';
 
+import '../../gallery/demo.dart';
+
 class TwoLevelListDemo extends StatelessWidget {
   static const String routeName = '/material/two-level-list';
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Expand/collapse list control')),
+      appBar: AppBar(
+        title: const Text('Expand/collapse list control'),
+        actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
+      ),
       body: ListView(
         children: <Widget>[
           const ListTile(title: Text('Top')),

examples/flutter_gallery/lib/gallery/demo.dart

@@ -2,8 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
+import 'package:url_launcher/url_launcher.dart';
 
+import 'demos.dart';
 import 'example_code_parser.dart';
 import 'syntax_highlighter.dart';
 
@@ -12,24 +15,28 @@ class ComponentDemoTabData {
     this.demoWidget,
     this.exampleCodeTag,
     this.description,
-    this.tabName
+    this.tabName,
+    this.documentationUrl,
   });
 
   final Widget demoWidget;
   final String exampleCodeTag;
   final String description;
   final String tabName;
+  final String documentationUrl;
 
   @override
   bool operator==(Object other) {
     if (other.runtimeType != runtimeType)
       return false;
     final ComponentDemoTabData typedOther = other;
-    return typedOther.tabName == tabName && typedOther.description == description;
+    return typedOther.tabName == tabName
+        && typedOther.description == description
+        && typedOther.documentationUrl == documentationUrl;
   }
 
   @override
-  int get hashCode => hashValues(tabName.hashCode, description.hashCode);
+  int get hashCode => hashValues(tabName, description, documentationUrl);
 }
 
 class TabbedComponentDemoScaffold extends StatelessWidget {
@@ -52,6 +59,13 @@ class TabbedComponentDemoScaffold extends StatelessWidget {
     }
   }
 
+  void _showApiDocumentation(BuildContext context) {
+    final String url = demos[DefaultTabController.of(context).index].documentationUrl;
+    if (url != null) {
+      launch(url, forceWebView: true);
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     return DefaultTabController(
@@ -61,14 +75,20 @@ class TabbedComponentDemoScaffold extends StatelessWidget {
           title: Text(title),
           actions: (actions ?? <Widget>[])..addAll(
             <Widget>[
+              Builder(
+                builder: (BuildContext context) {
+                  return IconButton(
+                    icon: const Icon(Icons.library_books),
+                    onPressed: () => _showApiDocumentation(context),
+                  );
+                },
+              ),
               Builder(
                 builder: (BuildContext context) {
                   return IconButton(
                     icon: const Icon(Icons.code),
                     tooltip: 'Show example code',
-                    onPressed: () {
-                      _showExampleCode(context);
-                    },
+                    onPressed: () => _showExampleCode(context),
                   );
                 },
               )
@@ -170,3 +190,44 @@ class FullScreenCodeDialogState extends State<FullScreenCodeDialog> {
     );
   }
 }
+
+class MaterialDemoDocumentationButton extends StatelessWidget {
+  MaterialDemoDocumentationButton(String routeName, { Key key })
+    : documentationUrl = kDemoDocumentationUrl[routeName],
+      assert(
+        kDemoDocumentationUrl[routeName] != null,
+        'A documentation URL was not specified for demo route $routeName in kAllGalleryDemos',
+      ),
+      super(key: key);
+
+  final String documentationUrl;
+
+  @override
+  Widget build(BuildContext context) {
+    return IconButton(
+      icon: const Icon(Icons.library_books),
+      onPressed: () => launch(documentationUrl, forceWebView: true)
+    );
+  }
+}
+
+class CupertinoDemoDocumentationButton extends StatelessWidget {
+  CupertinoDemoDocumentationButton(String routeName, { Key key })
+    : documentationUrl = kDemoDocumentationUrl[routeName],
+      assert(
+        kDemoDocumentationUrl[routeName] != null,
+        'A documentation URL was not specified for demo route $routeName in kAllGalleryDemos',
+      ),
+      super(key: key);
+
+  final String documentationUrl;
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoButton(
+      padding: EdgeInsets.zero,
+      child: const Icon(CupertinoIcons.book),
+      onPressed: () => launch(documentationUrl, forceWebView: true)
+    );
+  }
+}