Defer load demos

golden_test/demo_test.dart

@@ -18,6 +18,7 @@ void main() {
   group('mobile', () {
     testWidgets('demo page matches golden screenshot', (tester) async {
       await setUpBinding(tester);
+      await tester.runAsync<void>(pumpDeferredLibraries);
       await pumpWidgetWithImages(
         tester,
         const GalleryApp(initialRoute: demoBannerRoute),
@@ -33,6 +34,7 @@ void main() {
 
     testWidgets('dark demo page matches golden screenshot', (tester) async {
       await setUpBinding(tester, brightness: Brightness.dark);
+      await tester.runAsync<void>(pumpDeferredLibraries);
       await pumpWidgetWithImages(
         tester,
         const GalleryApp(initialRoute: demoBannerRoute),
@@ -50,6 +52,7 @@ void main() {
   group('desktop', () {
     testWidgets('demo page matches golden screenshot', (tester) async {
       await setUpBinding(tester, size: desktopSize);
+      await tester.runAsync<void>(pumpDeferredLibraries);
       await pumpWidgetWithImages(
         tester,
         const GalleryApp(initialRoute: demoBannerRoute),
@@ -69,6 +72,7 @@ void main() {
         size: desktopSize,
         brightness: Brightness.dark,
       );
+      await tester.runAsync<void>(pumpDeferredLibraries);
       await pumpWidgetWithImages(
         tester,
         const GalleryApp(initialRoute: demoBannerRoute),

lib/deferred_widget.dart

@@ -0,0 +1,73 @@
+// Copyright 2019 The Flutter team. 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:async';
+import 'package:flutter/material.dart';
+
+typedef LibraryLoader = Future<void> Function();
+typedef DeferredWidgetBuilder = Widget Function();
+
+/// Wraps the child inside a deferred module loader.
+///
+/// The child is created and a single instance of the Widget is maintained in
+/// state as long as closure to create widget stays the same.
+///
+class DeferredWidget extends StatefulWidget {
+  DeferredWidget(this.libraryLoader, this.createWidget, {Key key})
+      : super(key: key);
+
+  final LibraryLoader libraryLoader;
+  final DeferredWidgetBuilder createWidget;
+  static final Map<LibraryLoader, Future<void>> _moduleLoaders = {};
+  static final Set<LibraryLoader> _loadedModules = {};
+
+  static Future<void> preload(LibraryLoader loader) {
+    if (!_moduleLoaders.containsKey(loader)) {
+      _moduleLoaders[loader] = loader().then((dynamic _) {
+        _loadedModules.add(loader);
+      });
+    }
+    return _moduleLoaders[loader];
+  }
+
+  @override
+  _DeferredWidgetState createState() => _DeferredWidgetState();
+}
+
+class _DeferredWidgetState extends State<DeferredWidget> {
+  _DeferredWidgetState();
+  Widget _loadedChild;
+  DeferredWidgetBuilder _loadedCreator;
+
+  @override
+  void initState() {
+    /// If module was already loaded immediately create widget instead of
+    /// waiting for future or zone turn.
+    if (DeferredWidget._loadedModules.contains(widget.libraryLoader)) {
+      _onLibraryLoaded();
+    } else {
+      DeferredWidget.preload(widget.libraryLoader)
+          .then((dynamic _) => _onLibraryLoaded());
+    }
+    super.initState();
+  }
+
+  void _onLibraryLoaded() {
+    setState(() {
+      _loadedCreator = widget.createWidget;
+      _loadedChild = _loadedCreator();
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    /// If closure to create widget changed, create new instance, otherwise
+    /// treat as const Widget.
+    if (_loadedCreator != widget.createWidget && _loadedCreator != null) {
+      _loadedCreator = widget.createWidget;
+      _loadedChild = _loadedCreator();
+    }
+    return _loadedChild ?? Container();
+  }
+}

lib/demos/cupertino/cupertino_alert_demo.dart

@@ -6,17 +6,10 @@ import 'package:flutter/cupertino.dart';
 
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
 import 'package:gallery/data/gallery_options.dart';
+import 'package:gallery/demos/cupertino/demo_types.dart';
 
 // BEGIN cupertinoAlertDemo
 
-enum AlertDemoType {
-  alert,
-  alertTitle,
-  alertButtons,
-  alertButtonsOnly,
-  actionSheet,
-}
-
 class CupertinoAlertDemo extends StatefulWidget {
   const CupertinoAlertDemo({
     Key key,

lib/demos/cupertino/cupertino_demos.dart

@@ -0,0 +1,12 @@
+export 'package:gallery/demos/cupertino/cupertino_activity_indicator_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_alert_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_button_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_context_menu_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_navigation_bar_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_picker_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_refresh_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_segmented_control_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_slider_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_switch_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_tab_bar_demo.dart';
+export 'package:gallery/demos/cupertino/cupertino_text_field_demo.dart';

lib/demos/cupertino/demo_types.dart

@@ -0,0 +1,7 @@
+enum AlertDemoType {
+  alert,
+  alertTitle,
+  alertButtons,
+  alertButtonsOnly,
+  actionSheet,
+}

lib/demos/material/bottom_navigation_demo.dart

@@ -5,15 +5,11 @@
 import 'package:flutter/material.dart';
 import 'package:animations/animations.dart';
 
+import 'package:gallery/demos/material/material_demo_types.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
 
 // BEGIN bottomNavigationDemo
 
-enum BottomNavigationDemoType {
-  withLabels,
-  withoutLabels,
-}
-
 class BottomNavigationDemo extends StatefulWidget {
   const BottomNavigationDemo({
     Key key,

lib/demos/material/bottom_sheet_demo.dart

@@ -5,11 +5,7 @@
 import 'package:flutter/material.dart';
 
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
-
-enum BottomSheetDemoType {
-  persistent,
-  modal,
-}
+import 'package:gallery/demos/material/material_demo_types.dart';
 
 class BottomSheetDemo extends StatelessWidget {
   const BottomSheetDemo({

lib/demos/material/button_demo.dart

@@ -5,14 +5,7 @@
 import 'package:flutter/material.dart';
 
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
-
-enum ButtonDemoType {
-  text,
-  elevated,
-  outlined,
-  toggle,
-  floating,
-}
+import 'package:gallery/demos/material/material_demo_types.dart';
 
 class ButtonDemo extends StatelessWidget {
   const ButtonDemo({Key key, this.type}) : super(key: key);

lib/demos/material/chip_demo.dart

@@ -4,13 +4,7 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
-
-enum ChipDemoType {
-  action,
-  choice,
-  filter,
-  input,
-}
+import 'package:gallery/demos/material/material_demo_types.dart';
 
 class ChipDemo extends StatelessWidget {
   const ChipDemo({

lib/demos/material/dialog_demo.dart

@@ -5,17 +5,11 @@
 import 'package:flutter/material.dart';
 
 import 'package:gallery/data/gallery_options.dart';
+import 'package:gallery/demos/material/material_demo_types.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
 
 // BEGIN dialogDemo
 
-enum DialogDemoType {
-  alert,
-  alertTitle,
-  simple,
-  fullscreen,
-}
-
 class DialogDemo extends StatelessWidget {
   DialogDemo({Key key, @required this.type}) : super(key: key);
 

lib/demos/material/divider_demo.dart

@@ -3,13 +3,9 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+import 'package:gallery/demos/material/material_demo_types.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
 
-enum DividerDemoType {
-  horizontal,
-  vertical,
-}
-
 class DividerDemo extends StatelessWidget {
   const DividerDemo({Key key, this.type}) : super(key: key);
 

lib/demos/material/grid_list_demo.dart

@@ -4,15 +4,10 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
+import 'package:gallery/demos/material/material_demo_types.dart';
 
 // BEGIN gridListsDemo
 
-enum GridListDemoType {
-  imageOnly,
-  header,
-  footer,
-}
-
 class GridListDemo extends StatelessWidget {
   const GridListDemo({Key key, this.type}) : super(key: key);
 

lib/demos/material/list_demo.dart

@@ -5,14 +5,10 @@
 import 'package:flutter/material.dart';
 
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
+import 'package:gallery/demos/material/material_demo_types.dart';
 
 // BEGIN listDemo
 
-enum ListDemoType {
-  oneLine,
-  twoLine,
-}
-
 class ListDemo extends StatelessWidget {
   const ListDemo({Key key, this.type}) : super(key: key);
 

lib/demos/material/material_demo_types.dart

@@ -0,0 +1,82 @@
+enum BottomNavigationDemoType {
+  withLabels,
+  withoutLabels,
+}
+
+enum BottomSheetDemoType {
+  persistent,
+  modal,
+}
+
+enum ButtonDemoType {
+  text,
+  elevated,
+  outlined,
+  toggle,
+  floating,
+}
+
+enum ChipDemoType {
+  action,
+  choice,
+  filter,
+  input,
+}
+
+enum DialogDemoType {
+  alert,
+  alertTitle,
+  simple,
+  fullscreen,
+}
+
+enum GridListDemoType {
+  imageOnly,
+  header,
+  footer,
+}
+
+enum ListDemoType {
+  oneLine,
+  twoLine,
+}
+
+enum MenuDemoType {
+  contextMenu,
+  sectionedMenu,
+  simpleMenu,
+  checklistMenu,
+}
+
+enum PickerDemoType {
+  date,
+  time,
+  range,
+}
+
+enum ProgressIndicatorDemoType {
+  circular,
+  linear,
+}
+
+enum SelectionControlsDemoType {
+  checkbox,
+  radio,
+  switches,
+}
+
+enum SlidersDemoType {
+  sliders,
+  rangeSliders,
+  customSliders,
+}
+
+enum TabsDemoType {
+  scrollable,
+  nonScrollable,
+}
+
+enum DividerDemoType {
+  horizontal,
+  vertical,
+}

lib/demos/material/material_demos.dart

@@ -0,0 +1,24 @@
+export 'package:gallery/demos/material/banner_demo.dart';
+export 'package:gallery/demos/material/bottom_app_bar_demo.dart';
+export 'package:gallery/demos/material/bottom_navigation_demo.dart';
+export 'package:gallery/demos/material/bottom_sheet_demo.dart';
+export 'package:gallery/demos/material/button_demo.dart';
+export 'package:gallery/demos/material/cards_demo.dart';
+export 'package:gallery/demos/material/chip_demo.dart';
+export 'package:gallery/demos/material/data_table_demo.dart';
+export 'package:gallery/demos/material/dialog_demo.dart';
+export 'package:gallery/demos/material/divider_demo.dart';
+export 'package:gallery/demos/material/grid_list_demo.dart';
+export 'package:gallery/demos/material/list_demo.dart';
+export 'package:gallery/demos/material/menu_demo.dart';
+export 'package:gallery/demos/material/navigation_drawer.dart';
+export 'package:gallery/demos/material/navigation_rail_demo.dart';
+export 'package:gallery/demos/material/picker_demo.dart';
+export 'package:gallery/demos/material/progress_indicator_demo.dart';
+export 'package:gallery/demos/material/selection_controls_demo.dart';
+export 'package:gallery/demos/material/sliders_demo.dart';
+export 'package:gallery/demos/material/snackbar_demo.dart';
+export 'package:gallery/demos/material/tabs_demo.dart';
+export 'package:gallery/demos/material/text_field_demo.dart';
+export 'package:gallery/demos/material/tooltip_demo.dart';
+export 'package:gallery/demos/material/app_bar_demo.dart';

lib/demos/material/menu_demo.dart

@@ -5,13 +5,7 @@
 import 'package:flutter/material.dart';
 
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
-
-enum MenuDemoType {
-  contextMenu,
-  sectionedMenu,
-  simpleMenu,
-  checklistMenu,
-}
+import 'package:gallery/demos/material/material_demo_types.dart';
 
 enum SimpleValue {
   one,