Update examples to null safety (#732)

* Make ReadMe examples null-safe & fix errors.

* Make example project null safe.

* Fix most linter warnings.

README.md

@@ -479,40 +479,41 @@ Unable to find a matching variant of project :unityLibrary:
 
 ```dart
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
 import 'package:flutter_unity_widget/flutter_unity_widget.dart';
 
 void main() {
-  runApp(MaterialApp(
-    home: UnityDemoScreen()
-  ));
+  runApp(
+    const MaterialApp(
+      home: UnityDemoScreen(),
+    ),
+  );
 }
 
 class UnityDemoScreen extends StatefulWidget {
-
-  UnityDemoScreen({Key key}) : super(key: key);
+  const UnityDemoScreen({Key? key}) : super(key: key);
 
   @override
-  _UnityDemoScreenState createState() => _UnityDemoScreenState();
+  State<UnityDemoScreen> createState() => _UnityDemoScreenState();
 }
 
-class _UnityDemoScreenState extends State<UnityDemoScreen>{
+class _UnityDemoScreenState extends State<UnityDemoScreen> {
   static final GlobalKey<ScaffoldState> _scaffoldKey =
       GlobalKey<ScaffoldState>();
-  UnityWidgetController _unityWidgetController;
+  UnityWidgetController? _unityWidgetController;
 
+  @override
   Widget build(BuildContext context) {
-
     return Scaffold(
       key: _scaffoldKey,
       body: SafeArea(
         bottom: false,
         child: WillPopScope(
-          onWillPop: () {
+          onWillPop: () async {
             // Pop the category page if Android back button is pressed.
+            return true;
           },
           child: Container(
-            color: colorYellow,
+            color: Colors.yellow,
             child: UnityWidget(
               onUnityCreated: onUnityCreated,
             ),
@@ -524,9 +525,10 @@ class _UnityDemoScreenState extends State<UnityDemoScreen>{
 
   // Callback that connects the created controller to the unity controller
   void onUnityCreated(controller) {
-    this._unityWidgetController = controller;
+    _unityWidgetController = controller;
   }
 }
+
 ```
 <br />
 
@@ -536,17 +538,19 @@ class _UnityDemoScreenState extends State<UnityDemoScreen>{
 import 'package:flutter/material.dart';
 import 'package:flutter_unity_widget/flutter_unity_widget.dart';
 
-void main() => runApp(MyApp());
+void main() => runApp(const MyApp());
 
 class MyApp extends StatefulWidget {
+  const MyApp({Key? key}) : super(key: key);
+
   @override
-  _MyAppState createState() => _MyAppState();
+  State<MyApp> createState() => _MyAppState();
 }
 
 class _MyAppState extends State<MyApp> {
   static final GlobalKey<ScaffoldState> _scaffoldKey =
       GlobalKey<ScaffoldState>();
-  UnityWidgetController _unityWidgetController;
+  UnityWidgetController? _unityWidgetController;
   double _sliderValue = 0.0;
 
   @override
@@ -571,10 +575,10 @@ class _MyAppState extends State<MyApp> {
           child: Stack(
             children: <Widget>[
               UnityWidget(
-                  onUnityCreated: onUnityCreated,
-                  onUnityMessage: onUnityMessage,
-                  onUnitySceneLoaded: onUnitySceneLoaded,
-                  fullscreen: false,
+                onUnityCreated: onUnityCreated,
+                onUnityMessage: onUnityMessage,
+                onUnitySceneLoaded: onUnitySceneLoaded,
+                fullscreen: false,
               ),
               Positioned(
                 bottom: 20,
@@ -584,8 +588,8 @@ class _MyAppState extends State<MyApp> {
                   elevation: 10,
                   child: Column(
                     children: <Widget>[
-                      Padding(
-                        padding: const EdgeInsets.only(top: 20),
+                      const Padding(
+                        padding: EdgeInsets.only(top: 20),
                         child: Text("Rotation speed:"),
                       ),
                       Slider(
@@ -612,7 +616,7 @@ class _MyAppState extends State<MyApp> {
 
   // Communcation from Flutter to Unity
   void setRotationSpeed(String speed) {
-    _unityWidgetController.postMessage(
+    _unityWidgetController?.postMessage(
       'Cube',
       'SetRotationSpeed',
       speed,
@@ -626,15 +630,17 @@ class _MyAppState extends State<MyApp> {
 
   // Callback that connects the created controller to the unity controller
   void onUnityCreated(controller) {
-    this._unityWidgetController = controller;
+    _unityWidgetController = controller;
   }
 
   // Communication from Unity when new scene is loaded to Flutter
-  void onUnitySceneLoaded(SceneLoaded sceneInfo) {
-    print('Received scene loaded from unity: ${sceneInfo.name}');
-    print('Received scene loaded from unity buildIndex: ${sceneInfo.buildIndex}');
+  void onUnitySceneLoaded(SceneLoaded? sceneInfo) {
+    if (sceneInfo != null) {
+      print('Received scene loaded from unity: ${sceneInfo.name}');
+      print(
+          'Received scene loaded from unity buildIndex: ${sceneInfo.buildIndex}');
+    }
   }
-
 }
 
 ```

example/lib/main.dart

@@ -8,10 +8,12 @@ import 'screens/loader_screen.dart';
 import 'screens/simple_screen.dart';
 
 void main() {
-  runApp(MyApp());
+  runApp(const MyApp());
 }
 
 class MyApp extends StatelessWidget {
+  const MyApp({Key? key}) : super(key: key);
+
   // This widget is the root of your application.
   @override
   Widget build(BuildContext context) {
@@ -23,12 +25,12 @@ class MyApp extends StatelessWidget {
       ),
       initialRoute: '/',
       routes: {
-        '/': (context) => MenuScreen(),
-        '/simple': (context) => SimpleScreen(),
-        '/loader': (context) => LoaderScreen(),
-        '/orientation': (context) => OrientationScreen(),
-        '/api': (context) => ApiScreen(),
-        '/none': (context) => NoInteractionScreen(),
+        '/': (context) => const MenuScreen(),
+        '/simple': (context) => const SimpleScreen(),
+        '/loader': (context) => const LoaderScreen(),
+        '/orientation': (context) => const OrientationScreen(),
+        '/api': (context) => const ApiScreen(),
+        '/none': (context) => const NoInteractionScreen(),
       },
     );
   }

example/lib/menu_screen.dart

@@ -1,48 +1,48 @@
 import 'package:flutter/material.dart';
 
 class MenuScreen extends StatefulWidget {
-  MenuScreen({Key key}) : super(key: key);
+  const MenuScreen({Key? key}) : super(key: key);
 
   @override
-  _MenuScreenState createState() => _MenuScreenState();
+  State<MenuScreen> createState() => _MenuScreenState();
 }
 
 class _MenuScreenState extends State<MenuScreen> {
   bool enableAR = true;
 
   List<_MenuListItem> menus = [
-    new _MenuListItem(
+    _MenuListItem(
       description: 'Simple demonstration of unity flutter library',
       route: '/simple',
       title: 'Simple Unity Demo',
       enableAR: false,
     ),
-    new _MenuListItem(
+    _MenuListItem(
       description: 'No interaction of unity flutter library',
       route: '/none',
       title: 'No Interaction Unity Demo',
       enableAR: false,
     ),
-    new _MenuListItem(
+    _MenuListItem(
       description: 'Unity load and unload unity demo',
       route: '/loader',
       title: 'Safe mode Demo',
       enableAR: false,
     ),
-    new _MenuListItem(
+    _MenuListItem(
       description:
           'This example shows various native API exposed by the library',
       route: '/api',
       title: 'Native exposed API demo',
       enableAR: false,
     ),
-    new _MenuListItem(
+    _MenuListItem(
       title: 'Test Orientation',
       route: '/orientation',
       description: 'test orientation change',
       enableAR: false,
     ),
-    new _MenuListItem(
+    _MenuListItem(
       description: 'Unity native activity demo',
       route: '/activity',
       title: 'Native Activity Demo ',
@@ -54,17 +54,19 @@ class _MenuScreenState extends State<MenuScreen> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text('Menu List'),
+        title: const Text('Menu List'),
         actions: [
           Row(
             children: [
-              Text("Enable AR"),
+              const Text("Enable AR"),
               Checkbox(
                 value: enableAR,
                 onChanged: (changed) {
-                  setState(() {
-                    enableAR = changed;
-                  });
+                  if (changed != null) {
+                    setState(() {
+                      enableAR = changed;
+                    });
+                  }
                 },
               ),
             ],
@@ -97,5 +99,10 @@ class _MenuListItem {
   final String route;
   final bool enableAR;
 
-  _MenuListItem({this.title, this.description, this.route, this.enableAR});
+  _MenuListItem({
+    required this.title,
+    required this.description,
+    required this.route,
+    required this.enableAR,
+  });
 }