Add flutter_lints to form_app (#822)

form_app/analysis_options.yaml

@@ -0,0 +1,19 @@
+include: package:flutter_lints/flutter.yaml
+
+analyzer:
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+
+linter:
+  rules:
+    avoid_types_on_closure_parameters: true
+    avoid_void_async: true
+    cancel_subscriptions: true
+    close_sinks: true
+    directives_ordering: true
+    package_api_docs: true
+    package_prefixed_library_names: true
+    test_types_in_equals: true
+    throw_in_finally: true
+    unnecessary_statements: true

form_app/android/app/build.gradle

@@ -26,21 +26,17 @@ apply plugin: 'kotlin-android'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 28
+    compileSdkVersion 30
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'
     }
 
-    lintOptions {
-        disable 'InvalidPackage'
-    }
-
     defaultConfig {
         // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId "dev.flutter.formApp.form_app"
         minSdkVersion 16
-        targetSdkVersion 28
+        targetSdkVersion 30
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName
     }

form_app/android/app/src/main/AndroidManifest.xml

@@ -1,12 +1,6 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="dev.flutter.formApp.form_app">
-    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
+   <application
-         calls FlutterMain.startInitialization(this); in its onCreate method.
-         In most cases you can leave this as-is, but you if you want to provide
-         additional functionality it is fine to subclass or reimplement
-         FlutterApplication and put your custom class here. -->
-    <application
-        android:name="io.flutter.app.FlutterApplication"
         android:label="form_app"
         android:icon="@mipmap/ic_launcher">
         <activity

form_app/android/app/src/main/res/drawable-v21/launch_background.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="?android:colorBackground" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>

form_app/android/app/src/main/res/values-night/styles.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is on -->
+    <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <!-- Show a splash screen on the activity. Automatically removed when
+             Flutter draws its first frame -->
+        <item name="android:windowBackground">@drawable/launch_background</item>
+    </style>
+    <!-- Theme applied to the Android Window as soon as the process has started.
+         This theme determines the color of the Android Window while your
+         Flutter UI initializes, as well as behind your Flutter UI while its
+         running.
+         
+         This Theme is only used starting with V2 of Flutter's Android embedding. -->
+    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <item name="android:windowBackground">?android:colorBackground</item>
+    </style>
+</resources>

form_app/android/app/src/main/res/values/styles.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <!-- Theme applied to the Android Window while the process is starting -->
+    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is off -->
-    <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
+    <style name="LaunchTheme" parent="@android:style/Theme.Light.NoTitleBar">
         <!-- Show a splash screen on the activity. Automatically removed when
              Flutter draws its first frame -->
         <item name="android:windowBackground">@drawable/launch_background</item>
@@ -12,7 +12,7 @@
          running.
          
          This Theme is only used starting with V2 of Flutter's Android embedding. -->
-    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
+    <style name="NormalTheme" parent="@android:style/Theme.Light.NoTitleBar">
-        <item name="android:windowBackground">@android:color/white</item>
+        <item name="android:windowBackground">?android:colorBackground</item>
     </style>
 </resources>

form_app/android/build.gradle

@@ -6,7 +6,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.5.0'
+        classpath 'com.android.tools.build:gradle:4.1.0'
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
@@ -21,8 +21,6 @@ allprojects {
 rootProject.buildDir = '../build'
 subprojects {
     project.buildDir = "${rootProject.buildDir}/${project.name}"
-}
-subprojects {
     project.evaluationDependsOn(':app')
 }
 

form_app/android/gradle.properties

@@ -1,4 +1,3 @@
 org.gradle.jvmargs=-Xmx1536M
-android.enableR8=true
 android.useAndroidX=true
 android.enableJetifier=true

form_app/android/gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.6.2-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.7-all.zip

form_app/android/settings.gradle

@@ -1,7 +1,3 @@
-// Copyright 2014 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
 include ':app'
 
 def localPropertiesFile = new File(rootProject.projectDir, "local.properties")

form_app/ios/.gitignore

@@ -18,6 +18,7 @@ Flutter/App.framework
 Flutter/Flutter.framework
 Flutter/Flutter.podspec
 Flutter/Generated.xcconfig
+Flutter/ephemeral/
 Flutter/app.flx
 Flutter/app.zip
 Flutter/flutter_assets/

form_app/ios/Flutter/AppFrameworkInfo.plist

@@ -3,7 +3,7 @@
 <plist version="1.0">
 <dict>
   <key>CFBundleDevelopmentRegion</key>
-  <string>$(DEVELOPMENT_LANGUAGE)</string>
+  <string>en</string>
   <key>CFBundleExecutable</key>
   <string>App</string>
   <key>CFBundleIdentifier</key>

form_app/ios/Runner.xcodeproj/project.pbxproj

@@ -272,7 +272,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SUPPORTED_PLATFORMS = iphoneos;
@@ -289,16 +289,8 @@
 				CLANG_ENABLE_MODULES = YES;
 				CURRENT_PROJECT_VERSION = "$(FLUTTER_BUILD_NUMBER)";
 				ENABLE_BITCODE = NO;
-				FRAMEWORK_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Flutter",
-				);
 				INFOPLIST_FILE = Runner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
-				LIBRARY_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Flutter",
-				);
 				PRODUCT_BUNDLE_IDENTIFIER = dev.flutter.formApp.formApp;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OBJC_BRIDGING_HEADER = "Runner/Runner-Bridging-Header.h";
@@ -354,7 +346,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
 				MTL_ENABLE_DEBUG_INFO = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
@@ -403,7 +395,7 @@
 				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
 				GCC_WARN_UNUSED_FUNCTION = YES;
 				GCC_WARN_UNUSED_VARIABLE = YES;
-				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SUPPORTED_PLATFORMS = iphoneos;
@@ -421,16 +413,8 @@
 				CLANG_ENABLE_MODULES = YES;
 				CURRENT_PROJECT_VERSION = "$(FLUTTER_BUILD_NUMBER)";
 				ENABLE_BITCODE = NO;
-				FRAMEWORK_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Flutter",
-				);
 				INFOPLIST_FILE = Runner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
-				LIBRARY_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Flutter",
-				);
 				PRODUCT_BUNDLE_IDENTIFIER = dev.flutter.formApp.formApp;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OBJC_BRIDGING_HEADER = "Runner/Runner-Bridging-Header.h";
@@ -448,16 +432,8 @@
 				CLANG_ENABLE_MODULES = YES;
 				CURRENT_PROJECT_VERSION = "$(FLUTTER_BUILD_NUMBER)";
 				ENABLE_BITCODE = NO;
-				FRAMEWORK_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Flutter",
-				);
 				INFOPLIST_FILE = Runner/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks";
-				LIBRARY_SEARCH_PATHS = (
-					"$(inherited)",
-					"$(PROJECT_DIR)/Flutter",
-				);
 				PRODUCT_BUNDLE_IDENTIFIER = dev.flutter.formApp.formApp;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OBJC_BRIDGING_HEADER = "Runner/Runner-Bridging-Header.h";

form_app/ios/Runner.xcodeproj/project.xcworkspace/contents.xcworkspacedata

@@ -2,6 +2,6 @@
 <Workspace
    version = "1.0">
    <FileRef
-      location = "group:Runner.xcodeproj">
+      location = "self:">
    </FileRef>
 </Workspace>

form_app/lib/main.dart

@@ -15,7 +15,7 @@ import 'src/validation.dart';
 final http.Client httpClient = MockClient();
 
 void main() {
-  runApp(FormApp());
+  runApp(const FormApp());
 }
 
 final demos = [
@@ -29,41 +29,44 @@ final demos = [
   Demo(
     name: 'Autofill',
     route: '/autofill',
-    builder: (context) => AutofillDemo(),
+    builder: (context) => const AutofillDemo(),
   ),
   Demo(
     name: 'Form widgets',
     route: '/form_widgets',
-    builder: (context) => FormWidgetsDemo(),
+    builder: (context) => const FormWidgetsDemo(),
   ),
   Demo(
     name: 'Validation',
     route: '/validation',
-    builder: (context) => FormValidationDemo(),
+    builder: (context) => const FormValidationDemo(),
   ),
 ];
 
 class FormApp extends StatelessWidget {
+  const FormApp({Key key}) : super(key: key);
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
       title: 'Form Samples',
       theme: ThemeData(primarySwatch: Colors.teal),
       routes: Map.fromEntries(demos.map((d) => MapEntry(d.route, d.builder))),
-      home: HomePage(),
+      home: const HomePage(),
     );
   }
 }
 
 class HomePage extends StatelessWidget {
+  const HomePage({Key key}) : super(key: key);
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text('Form Samples'),
+        title: const Text('Form Samples'),
       ),
       body: ListView(
-        children: [...demos.map((d) => DemoTile(d))],
+        children: [...demos.map((d) => DemoTile(demo: d))],
       ),
     );
   }
@@ -72,7 +75,7 @@ class HomePage extends StatelessWidget {
 class DemoTile extends StatelessWidget {
   final Demo demo;
 
-  DemoTile(this.demo);
+  const DemoTile({this.demo, Key key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {

form_app/lib/src/autofill.dart

@@ -7,6 +7,8 @@ import 'package:flutter/material.dart';
 // Demonstrates how to use autofill hints. The full list of hints is here:
 // https://github.com/flutter/engine/blob/master/lib/web_ui/lib/src/engine/text_editing/autofill_hint.dart
 class AutofillDemo extends StatefulWidget {
+  const AutofillDemo({Key key}) : super(key: key);
+
   @override
   _AutofillDemoState createState() => _AutofillDemoState();
 }
@@ -18,36 +20,36 @@ class _AutofillDemoState extends State<AutofillDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text('Autofill'),
+        title: const Text('Autofill'),
       ),
       body: Form(
         key: _formKey,
         child: Scrollbar(
           child: SingleChildScrollView(
-            padding: EdgeInsets.all(16),
+            padding: const EdgeInsets.all(16),
             child: AutofillGroup(
               child: Column(
                 children: [
                   ...[
-                    Text('This sample demonstrates autofill. '),
+                    const Text('This sample demonstrates autofill. '),
                     TextFormField(
                       autofocus: true,
                       textInputAction: TextInputAction.next,
-                      decoration: InputDecoration(
+                      decoration: const InputDecoration(
                         hintText: 'Jane',
                         labelText: 'First Name',
                       ),
-                      autofillHints: [AutofillHints.givenName],
+                      autofillHints: const [AutofillHints.givenName],
                     ),
                     TextFormField(
                       textInputAction: TextInputAction.next,
-                      decoration: InputDecoration(
+                      decoration: const InputDecoration(
                         hintText: 'Doe',
                         labelText: 'Last Name',
                       ),
-                      autofillHints: [AutofillHints.familyName],
+                      autofillHints: const [AutofillHints.familyName],
                     ),
-                    TextField(
+                    const TextField(
                       keyboardType: TextInputType.emailAddress,
                       textInputAction: TextInputAction.next,
                       decoration: InputDecoration(
@@ -56,7 +58,7 @@ class _AutofillDemoState extends State<AutofillDemo> {
                       ),
                       autofillHints: [AutofillHints.email],
                     ),
-                    TextField(
+                    const TextField(
                       keyboardType: TextInputType.phone,
                       textInputAction: TextInputAction.next,
                       decoration: InputDecoration(
@@ -65,7 +67,7 @@ class _AutofillDemoState extends State<AutofillDemo> {
                       ),
                       autofillHints: <String>[AutofillHints.telephoneNumber],
                     ),
-                    TextField(
+                    const TextField(
                       keyboardType: TextInputType.streetAddress,
                       textInputAction: TextInputAction.next,
                       decoration: InputDecoration(
@@ -74,7 +76,7 @@ class _AutofillDemoState extends State<AutofillDemo> {
                       ),
                       autofillHints: <String>[AutofillHints.streetAddressLine1],
                     ),
-                    TextField(
+                    const TextField(
                       keyboardType: TextInputType.number,
                       textInputAction: TextInputAction.next,
                       decoration: InputDecoration(
@@ -83,7 +85,7 @@ class _AutofillDemoState extends State<AutofillDemo> {
                       ),
                       autofillHints: <String>[AutofillHints.postalCode],
                     ),
-                    TextField(
+                    const TextField(
                       textInputAction: TextInputAction.next,
                       decoration: InputDecoration(
                         hintText: 'United States',
@@ -91,7 +93,7 @@ class _AutofillDemoState extends State<AutofillDemo> {
                       ),
                       autofillHints: <String>[AutofillHints.countryName],
                     ),
-                    TextField(
+                    const TextField(
                       keyboardType: TextInputType.number,
                       decoration: InputDecoration(
                         hintText: '1',
@@ -102,7 +104,7 @@ class _AutofillDemoState extends State<AutofillDemo> {
                   ].expand(
                     (widget) => [
                       widget,
-                      SizedBox(
+                      const SizedBox(
                         height: 24,
                       )
                     ],

form_app/lib/src/form_widgets.dart

@@ -6,6 +6,8 @@ import 'package:flutter/material.dart';
 import 'package:intl/intl.dart' as intl;
 
 class FormWidgetsDemo extends StatefulWidget {
+  const FormWidgetsDemo({Key key}) : super(key: key);
+
   @override
   _FormWidgetsDemoState createState() => _FormWidgetsDemoState();
 }
@@ -23,7 +25,7 @@ class _FormWidgetsDemoState extends State<FormWidgetsDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text('Form widgets'),
+        title: const Text('Form widgets'),
       ),
       body: Form(
         key: _formKey,
@@ -32,16 +34,16 @@ class _FormWidgetsDemoState extends State<FormWidgetsDemo> {
             alignment: Alignment.topCenter,
             child: Card(
               child: SingleChildScrollView(
-                padding: EdgeInsets.all(16),
+                padding: const EdgeInsets.all(16),
                 child: ConstrainedBox(
-                  constraints: BoxConstraints(maxWidth: 400),
+                  constraints: const BoxConstraints(maxWidth: 400),
                   child: Column(
                     mainAxisAlignment: MainAxisAlignment.center,
                     crossAxisAlignment: CrossAxisAlignment.center,
                     children: [
                       ...[
                         TextFormField(
-                          decoration: InputDecoration(
+                          decoration: const InputDecoration(
                             filled: true,
                             hintText: 'Enter a title...',
                             labelText: 'Title',
@@ -53,8 +55,8 @@ class _FormWidgetsDemoState extends State<FormWidgetsDemo> {
                           },
                         ),
                         TextFormField(
-                          decoration: InputDecoration(
+                          decoration: const InputDecoration(
-                            border: const OutlineInputBorder(),
+                            border: OutlineInputBorder(),
                             filled: true,
                             hintText: 'Enter a description...',
                             labelText: 'Description',
@@ -64,7 +66,7 @@ class _FormWidgetsDemoState extends State<FormWidgetsDemo> {
                           },
                           maxLines: 5,
                         ),
-                        _FormDatePicker(
+                        _FormDatePicker<DateTime>(
                           date: date,
                           onChanged: (value) {
                             setState(() {
@@ -139,7 +141,7 @@ class _FormWidgetsDemoState extends State<FormWidgetsDemo> {
                       ].expand(
                         (widget) => [
                           widget,
-                          SizedBox(
+                          const SizedBox(
                             height: 24,
                           )
                         ],
@@ -156,11 +158,11 @@ class _FormWidgetsDemoState extends State<FormWidgetsDemo> {
   }
 }
 
-class _FormDatePicker extends StatefulWidget {
+class _FormDatePicker<T> extends StatefulWidget {
   final DateTime date;
-  final ValueChanged onChanged;
+  final ValueChanged<T> onChanged;
 
-  _FormDatePicker({
+  const _FormDatePicker({
     this.date,
     this.onChanged,
   });
@@ -191,7 +193,7 @@ class _FormDatePickerState extends State<_FormDatePicker> {
           ],
         ),
         TextButton(
-          child: Text('Edit'),
+          child: const Text('Edit'),
           onPressed: () async {
             var newDate = await showDatePicker(
               context: context,

form_app/lib/src/http/mock_client.dart

@@ -11,10 +11,10 @@ class MockClient extends Mock implements http.Client {
   MockClient() {
     when(post('https://example.com/signin', body: anyNamed('body')))
         .thenAnswer((answering) {
-      var body = answering.namedArguments[Symbol('body')];
+      dynamic body = answering.namedArguments[const Symbol('body')];
 
       if (body != null && body is String) {
-        var decodedJson = json.decode(body);
+        var decodedJson = json.decode(body) as Map<String, String>;
 
         if (decodedJson['email'] == 'root' &&
             decodedJson['password'] == 'password') {

form_app/lib/src/sign_in_http.dart

@@ -29,9 +29,10 @@ class FormData {
 class SignInHttpDemo extends StatefulWidget {
   final http.Client httpClient;
 
-  SignInHttpDemo({
+  const SignInHttpDemo({
     this.httpClient,
-  });
+    Key key,
+  }) : super(key: key);
 
   @override
   _SignInHttpDemoState createState() => _SignInHttpDemoState();
@@ -44,19 +45,19 @@ class _SignInHttpDemoState extends State<SignInHttpDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text('Sign in Form'),
+        title: const Text('Sign in Form'),
       ),
       body: Form(
         child: Scrollbar(
           child: SingleChildScrollView(
-            padding: EdgeInsets.all(16),
+            padding: const EdgeInsets.all(16),
             child: Column(
               children: [
                 ...[
                   TextFormField(
-                    autofocus:  true,
+                    autofocus: true,
                     textInputAction: TextInputAction.next,
-                    decoration: InputDecoration(
+                    decoration: const InputDecoration(
                       filled: true,
                       hintText: 'Your email address',
                       labelText: 'Email',
@@ -66,7 +67,7 @@ class _SignInHttpDemoState extends State<SignInHttpDemo> {
                     },
                   ),
                   TextFormField(
-                    decoration: InputDecoration(
+                    decoration: const InputDecoration(
                       filled: true,
                       labelText: 'Password',
                     ),
@@ -76,7 +77,7 @@ class _SignInHttpDemoState extends State<SignInHttpDemo> {
                     },
                   ),
                   TextButton(
-                    child: Text('Sign in'),
+                    child: const Text('Sign in'),
                     onPressed: () async {
                       // Use a JSON encoded string to send
                       var result = await widget.httpClient.post(
@@ -96,7 +97,7 @@ class _SignInHttpDemoState extends State<SignInHttpDemo> {
                 ].expand(
                   (widget) => [
                     widget,
-                    SizedBox(
+                    const SizedBox(
                       height: 24,
                     )
                   ],
@@ -110,13 +111,13 @@ class _SignInHttpDemoState extends State<SignInHttpDemo> {
   }
 
   void _showDialog(String message) {
-    showDialog(
+    showDialog<void>(
       context: context,
       builder: (context) => AlertDialog(
         title: Text(message),
         actions: [
           TextButton(
-            child: Text('OK'),
+            child: const Text('OK'),
             onPressed: () => Navigator.of(context).pop(),
           ),
         ],

form_app/lib/src/validation.dart

@@ -6,6 +6,8 @@ import 'package:flutter/material.dart';
 import 'package:english_words/english_words.dart' as english_words;
 
 class FormValidationDemo extends StatefulWidget {
+  const FormValidationDemo({Key key}) : super(key: key);
+
   @override
   _FormValidationDemoState createState() => _FormValidationDemoState();
 }
@@ -20,13 +22,13 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: Text('📖 Story Generator'),
+        title: const Text('📖 Story Generator'),
         actions: [
           Padding(
-            padding: EdgeInsets.all(8),
+            padding: const EdgeInsets.all(8),
             child: TextButton(
               style: TextButton.styleFrom(primary: Colors.white),
-              child: Text('Submit'),
+              child: const Text('Submit'),
               onPressed: () {
                 // Validate the form by getting the FormState from the GlobalKey
                 // and calling validate() on it.
@@ -35,14 +37,14 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
                   return;
                 }
 
-                showDialog(
+                showDialog<void>(
                   context: context,
                   builder: (context) => AlertDialog(
-                    title: Text('Your story'),
+                    title: const Text('Your story'),
                     content: Text('The $adjective developer saw a $noun'),
                     actions: [
                       TextButton(
-                        child: Text('Done'),
+                        child: const Text('Done'),
                         onPressed: () {
                           Navigator.of(context).pop();
                         },
@@ -59,7 +61,7 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
         key: _formKey,
         child: Scrollbar(
           child: SingleChildScrollView(
-            padding: EdgeInsets.all(16),
+            padding: const EdgeInsets.all(16),
             child: Column(
               children: [
                 // A text field that validates that the text is an adjective.
@@ -75,7 +77,7 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
                     }
                     return 'Not a valid adjective.';
                   },
-                  decoration: InputDecoration(
+                  decoration: const InputDecoration(
                     filled: true,
                     hintText: 'e.g. quick, beautiful, interesting',
                     labelText: 'Enter an adjective',
@@ -84,7 +86,7 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
                     adjective = value;
                   },
                 ),
-                SizedBox(
+                const SizedBox(
                   height: 24,
                 ),
                 // A text field that validates that the text is a noun.
@@ -98,7 +100,7 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
                     }
                     return 'Not a valid noun.';
                   },
-                  decoration: InputDecoration(
+                  decoration: const InputDecoration(
                     filled: true,
                     hintText: 'i.e. a person, place or thing',
                     labelText: 'Enter a noun',
@@ -107,12 +109,12 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
                     noun = value;
                   },
                 ),
-                SizedBox(
+                const SizedBox(
                   height: 24,
                 ),
                 // A custom form field that requires the user to check a
                 // checkbox.
-                FormField(
+                FormField<bool>(
                   initialValue: false,
                   validator: (value) {
                     if (value == false) {
@@ -120,7 +122,7 @@ class _FormValidationDemoState extends State<FormValidationDemo> {
                     }
                     return null;
                   },
-                  builder: (FormFieldState formFieldState) {
+                  builder: (formFieldState) {
                     return Column(
                       crossAxisAlignment: CrossAxisAlignment.start,
                       children: [

form_app/pubspec.lock

@@ -202,6 +202,13 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_lints:
+    dependency: "direct dev"
+    description:
+      name: flutter_lints
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.3"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -277,6 +284,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "3.5.1"
+  lints:
+    dependency: transitive
+    description:
+      name: lints
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.1"
   logging:
     dependency: transitive
     description:

form_app/pubspec.yaml

@@ -1,6 +1,6 @@
 name: form_app
 description: A sample demonstrating different types of forms and best practices
-publish_to: 'none'
+publish_to: "none"
 version: 1.0.0+1
 
 environment:
@@ -21,5 +21,7 @@ dev_dependencies:
     sdk: flutter
   json_serializable: ^3.0.0
   build_runner: ^1.10.0
+  flutter_lints: ^1.0.0
+
 flutter:
   uses-material-design: true

form_app/web/index.html

@@ -1,6 +1,19 @@
 <!DOCTYPE html>
 <html>
+
 <head>
+  <!--
+    If you are serving your web app in a path other than the root, change the
+    href value below to reflect the base path you are serving from.
+
+    The path provided below has to start and end with a slash "/" in order for
+    it to work correctly.
+
+    For more details:
+    * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
+  -->
+  <base href="/">
+
   <meta charset="UTF-8">
   <meta content="IE=Edge" http-equiv="X-UA-Compatible">
   <meta name="description" content="A sample demonstrating different types of forms and best practices">
@@ -11,23 +24,78 @@
   <meta name="apple-mobile-web-app-title" content="form_app">
   <link rel="apple-touch-icon" href="icons/Icon-192.png">
 
-  <!-- Favicon -->
-  <link rel="shortcut icon" type="image/png" href="favicon.png"/>
-
   <title>form_app</title>
   <link rel="manifest" href="manifest.json">
 </head>
+
 <body>
   <!-- This script installs service_worker.js to provide PWA functionality to
        application. For more information, see:
        https://developers.google.com/web/fundamentals/primers/service-workers -->
   <script>
+    var serviceWorkerVersion = null;
+    var scriptLoaded = false;
+    function loadMainDartJs() {
+      if (scriptLoaded) {
+        return;
+      }
+      scriptLoaded = true;
+      var scriptTag = document.createElement('script');
+      scriptTag.src = 'main.dart.js';
+      scriptTag.type = 'application/javascript';
+      document.body.append(scriptTag);
+    }
+
     if ('serviceWorker' in navigator) {
+      // Service workers are supported. Use them.
       window.addEventListener('load', function () {
-        navigator.serviceWorker.register('flutter_service_worker.js');
+        // Wait for registration to finish before dropping the <script> tag.
+        // Otherwise, the browser will load the script multiple times,
+        // potentially different versions.
+        var serviceWorkerUrl = 'flutter_service_worker.js?v=' + serviceWorkerVersion;
+        navigator.serviceWorker.register(serviceWorkerUrl)
+          .then((reg) => {
+            function waitForActivation(serviceWorker) {
+              serviceWorker.addEventListener('statechange', () => {
+                if (serviceWorker.state == 'activated') {
+                  console.log('Installed new service worker.');
+                  loadMainDartJs();
+                }
+              });
+            }
+            if (!reg.active && (reg.installing || reg.waiting)) {
+              // No active web worker and we have installed or are installing
+              // one for the first time. Simply wait for it to activate.
+              waitForActivation(reg.installing ?? reg.waiting);
+            } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
+              // When the app updates the serviceWorkerVersion changes, so we
+              // need to ask the service worker to update.
+              console.log('New service worker available.');
+              reg.update();
+              waitForActivation(reg.installing);
+            } else {
+              // Existing service worker is still good.
+              console.log('Loading app from service worker.');
+              loadMainDartJs();
+            }
+          });
+
+        // If service worker doesn't succeed in a reasonable amount of time,
+        // fallback to plaint <script> tag.
+        setTimeout(() => {
+          if (!scriptLoaded) {
+            console.warn(
+              'Failed to load app from service worker. Falling back to plain <script> tag.',
+            );
+            loadMainDartJs();
+          }
+        }, 4000);
       });
+    } else {
+      // Service workers not supported. Just drop the <script> tag.
+      loadMainDartJs();
     }
   </script>
-  <script src="main.dart.js" type="application/javascript"></script>
 </body>
+
 </html>