made some progress

platform_design/lib/main.dart

@@ -0,0 +1,99 @@
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+
+import 'tab_1.dart';
+import 'tab_2.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Flutter Demo',
+      theme: ThemeData(
+        primarySwatch: Colors.green,
+      ),
+      builder: (BuildContext context, Widget child) {
+        return CupertinoTheme(
+          data: CupertinoThemeData(),
+          child: child,
+        );
+      },
+      home: PlatformAdaptingHomePage(),
+    );
+  }
+}
+
+class PlatformAdaptingHomePage extends StatefulWidget {
+  PlatformAdaptingHomePage({ Key key }) : super(key: key);
+
+  @override
+  _PlatformAdaptingHomePageState createState() => _PlatformAdaptingHomePageState();
+}
+
+class _PlatformAdaptingHomePageState extends State<PlatformAdaptingHomePage> {
+  final tab1Key = GlobalKey();
+  final tab2Key = GlobalKey();
+
+  Widget _buildAndroidHomePage() {
+    return Scaffold(
+      appBar: AppBar(title: Text(tab1Title)),
+      drawer: Drawer(
+
+      ),
+      body: Tab1(key: tab1Key),
+    );
+  }
+
+  Widget _buildIosHomePage() {
+    return CupertinoTabScaffold(
+      tabBar: CupertinoTabBar(
+        items: <BottomNavigationBarItem>[
+          BottomNavigationBarItem(
+            title: Text(tab1Title),
+            icon: tab1IosIcon,
+          ),
+          BottomNavigationBarItem(
+            title: Text(tab2Title),
+            icon: tab2IosIcon,
+          ),
+        ],
+      ),
+      tabBuilder: (BuildContext context, int index) {
+        switch (index) {
+          case 0:
+            return CupertinoTabView(
+              defaultTitle: tab1Title,
+              builder: (BuildContext context) {
+                return Tab1(key: tab1Key);
+              },
+            );
+          case 1:
+            return CupertinoTabView(
+              defaultTitle: tab2Title,
+              builder: (BuildContext context) {
+                return Tab2(key: tab2Key);
+              },
+            );
+        }
+      },
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+        return _buildAndroidHomePage();
+      case TargetPlatform.iOS:
+        return _buildIosHomePage();
+    }
+
+    assert(false, 'Unexpected platform');
+    return null;
+  }
+}
+