[Gallery] Fix directory structure (#312)

gallery/lib/pages/about.dart

@@ -0,0 +1,134 @@
+// 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 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:package_info/package_info.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+import 'package:gallery/l10n/gallery_localizations.dart';
+
+void showAboutDialog({
+  @required BuildContext context,
+}) {
+  assert(context != null);
+  showDialog<void>(
+    context: context,
+    builder: (context) {
+      return _AboutDialog();
+    },
+  );
+}
+
+Future<String> getVersionNumber() async {
+  PackageInfo packageInfo = await PackageInfo.fromPlatform();
+  return packageInfo.version;
+}
+
+class _AboutDialog extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+    final textTheme = Theme.of(context).textTheme;
+    final bodyTextStyle = textTheme.body2.apply(color: colorScheme.onPrimary);
+
+    final name = 'Flutter Gallery'; // Don't need to localize.
+    final legalese = '© 2019 The Flutter team'; // Don't need to localize.
+    final samplesRepo =
+        GalleryLocalizations.of(context).aboutFlutterSamplesRepo;
+    final seeSource =
+        GalleryLocalizations.of(context).aboutDialogDescription(samplesRepo);
+    final samplesRepoIndex = seeSource.indexOf(samplesRepo);
+    final samplesRepoIndexEnd = samplesRepoIndex + samplesRepo.length;
+    final seeSourceFirst = seeSource.substring(0, samplesRepoIndex);
+    final seeSourceSecond = seeSource.substring(samplesRepoIndexEnd);
+
+    return AlertDialog(
+      backgroundColor: colorScheme.background,
+      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
+      content: Container(
+        constraints: BoxConstraints(maxWidth: 400),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            FutureBuilder(
+              future: getVersionNumber(),
+              builder: (context, snapshot) => Text(
+                snapshot.hasData ? '$name ${snapshot.data}' : '$name',
+                style: textTheme.display1.apply(color: colorScheme.onPrimary),
+              ),
+            ),
+            SizedBox(height: 24),
+            RichText(
+              text: TextSpan(
+                children: [
+                  TextSpan(
+                    style: bodyTextStyle,
+                    text: seeSourceFirst,
+                  ),
+                  TextSpan(
+                    style: bodyTextStyle.copyWith(
+                      color: colorScheme.primary,
+                    ),
+                    text: samplesRepo,
+                    recognizer: TapGestureRecognizer()
+                      ..onTap = () async {
+                        final url = 'https://github.com/flutter/samples/';
+                        if (await canLaunch(url)) {
+                          await launch(
+                            url,
+                            forceSafariVC: false,
+                          );
+                        }
+                      },
+                  ),
+                  TextSpan(
+                    style: bodyTextStyle,
+                    text: seeSourceSecond,
+                  ),
+                ],
+              ),
+            ),
+            SizedBox(height: 18),
+            Text(
+              legalese,
+              style: bodyTextStyle,
+            ),
+          ],
+        ),
+      ),
+      actions: [
+        FlatButton(
+          textColor: colorScheme.primary,
+          child: Text(
+            MaterialLocalizations.of(context).viewLicensesButtonLabel,
+          ),
+          onPressed: () {
+            Navigator.of(context).push(MaterialPageRoute<void>(
+              builder: (context) => Theme(
+                data: Theme.of(context).copyWith(
+                  textTheme:
+                      Typography(platform: Theme.of(context).platform).black,
+                  scaffoldBackgroundColor: Colors.white,
+                ),
+                child: LicensePage(
+                  applicationName: name,
+                  applicationLegalese: legalese,
+                ),
+              ),
+            ));
+          },
+        ),
+        FlatButton(
+          textColor: colorScheme.primary,
+          child: Text(MaterialLocalizations.of(context).closeButtonLabel),
+          onPressed: () {
+            Navigator.pop(context);
+          },
+        ),
+      ],
+    );
+  }
+}