[Gallery] Fix directory structure (#312)

gallery/lib/demos/material/banner_demo.dart

@@ -0,0 +1,125 @@
+// Copyright 2020 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 'package:flutter/material.dart';
+import 'package:gallery/l10n/gallery_localizations.dart';
+
+// BEGIN bannerDemo
+
+enum BannerDemoAction {
+  reset,
+  showMultipleActions,
+  showLeading,
+}
+
+class BannerDemo extends StatefulWidget {
+  @override
+  _BannerDemoState createState() => _BannerDemoState();
+}
+
+class _BannerDemoState extends State<BannerDemo> {
+  static const _itemCount = 20;
+  var _displayBanner = true;
+  var _showMultipleActions = true;
+  var _showLeading = true;
+
+  void handleDemoAction(BannerDemoAction action) {
+    setState(() {
+      switch (action) {
+        case BannerDemoAction.reset:
+          _displayBanner = true;
+          _showMultipleActions = true;
+          _showLeading = true;
+          break;
+        case BannerDemoAction.showMultipleActions:
+          _showMultipleActions = !_showMultipleActions;
+          break;
+        case BannerDemoAction.showLeading:
+          _showLeading = !_showLeading;
+          break;
+      }
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+    final banner = MaterialBanner(
+      content: Text(GalleryLocalizations.of(context).bannerDemoText),
+      leading: _showLeading
+          ? CircleAvatar(
+              child: Icon(Icons.access_alarm, color: colorScheme.onPrimary),
+              backgroundColor: colorScheme.primary,
+            )
+          : null,
+      actions: [
+        FlatButton(
+          child: Text(GalleryLocalizations.of(context).signIn),
+          onPressed: () {
+            setState(() {
+              _displayBanner = false;
+            });
+          },
+        ),
+        if (_showMultipleActions)
+          FlatButton(
+            child: Text(GalleryLocalizations.of(context).dismiss),
+            onPressed: () {
+              setState(() {
+                _displayBanner = false;
+              });
+            },
+          ),
+      ],
+      backgroundColor: colorScheme.background,
+    );
+
+    return Scaffold(
+      appBar: AppBar(
+        automaticallyImplyLeading: false,
+        title: Text(GalleryLocalizations.of(context).demoBannerTitle),
+        actions: [
+          PopupMenuButton<BannerDemoAction>(
+            onSelected: handleDemoAction,
+            itemBuilder: (context) => <PopupMenuEntry<BannerDemoAction>>[
+              PopupMenuItem<BannerDemoAction>(
+                value: BannerDemoAction.reset,
+                child:
+                    Text(GalleryLocalizations.of(context).bannerDemoResetText),
+              ),
+              const PopupMenuDivider(),
+              CheckedPopupMenuItem<BannerDemoAction>(
+                value: BannerDemoAction.showMultipleActions,
+                checked: _showMultipleActions,
+                child: Text(
+                    GalleryLocalizations.of(context).bannerDemoMultipleText),
+              ),
+              CheckedPopupMenuItem<BannerDemoAction>(
+                value: BannerDemoAction.showLeading,
+                checked: _showLeading,
+                child: Text(
+                    GalleryLocalizations.of(context).bannerDemoLeadingText),
+              ),
+            ],
+          ),
+        ],
+      ),
+      body: ListView.builder(
+          itemCount: _displayBanner ? _itemCount + 1 : _itemCount,
+          itemBuilder: (context, index) {
+            if (index == 0 && _displayBanner) {
+              return banner;
+            }
+            return ListTile(
+              title: Text(
+                GalleryLocalizations.of(context)
+                    .starterAppDrawerItem(_displayBanner ? index : index + 1),
+              ),
+            );
+          }),
+    );
+  }
+}
+
+// END