Add a Material/Cupertino adaptive application example (#69)

platform_design/lib/settings_tab.dart

@@ -0,0 +1,104 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+
+import 'widgets.dart';
+
+class SettingsTab extends StatefulWidget {
+  static const title = 'Settings';
+  static const androidIcon = Icon(Icons.settings);
+  static const iosIcon = Icon(CupertinoIcons.gear);
+
+  @override
+  _SettingsTabState createState() => _SettingsTabState();
+}
+
+class _SettingsTabState extends State<SettingsTab> {
+  var switch1 = false; var switch2 = true; var switch3 = true; var switch4 = true;
+  var switch5 = true; var switch6 = false; var switch7 = true;
+
+  Widget _buildList() {
+    return ListView(
+      children: [
+        Padding(padding: EdgeInsets.only(top: 24)),
+        ListTile(
+          title: Text('Send me marketing emails'),
+          // The Material switch has a platform adaptive constructor.
+          trailing: Switch.adaptive(
+            value: switch1,
+            onChanged: (value) => setState(() => switch1 = value),
+          ),
+        ),
+        ListTile(
+          title: Text('Enable notifications'),
+          trailing: Switch.adaptive(
+            value: switch2,
+            onChanged: (value) => setState(() => switch2 = value),
+          ),
+        ),
+        ListTile(
+          title: Text('Remind me to rate this app'),
+          trailing: Switch.adaptive(
+            value: switch3,
+            onChanged: (value) => setState(() => switch3 = value),
+          ),
+        ),
+        ListTile(
+          title: Text('Background song refresh'),
+          trailing: Switch.adaptive(
+            value: switch4,
+            onChanged: (value) => setState(() => switch4 = value),
+          ),
+        ),
+        ListTile(
+          title: Text('Recommend me songs based on my location'),
+          trailing: Switch.adaptive(
+            value: switch5,
+            onChanged: (value) => setState(() => switch5 = value),
+          ),
+        ),
+        ListTile(
+          title: Text('Auto-transition playback to cast devices'),
+          trailing: Switch.adaptive(
+            value: switch6,
+            onChanged: (value) => setState(() => switch6 = value),
+          ),
+        ),
+        ListTile(
+          title: Text('Find friends from my contact list'),
+          trailing: Switch.adaptive(
+            value: switch7,
+            onChanged: (value) => setState(() => switch7 = value),
+          ),
+        ),
+      ],
+    );
+  }
+
+  // ===========================================================================
+  // Non-shared code below because this tab uses different scaffolds.
+  // ===========================================================================
+
+  Widget _buildAndroid(context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(SettingsTab.title),
+      ),
+      body: _buildList(),
+    );
+  }
+
+  Widget _buildIos(context) {
+    return CupertinoPageScaffold(
+      navigationBar: CupertinoNavigationBar(),
+      child: _buildList(),
+    );
+  }
+
+  @override
+  Widget build(context) {
+    return PlatformWidget(
+      androidBuilder: _buildAndroid,
+      iosBuilder: _buildIos,
+    );
+  }
+}