Samples maintenance (#435)

animations/lib/src/misc/animated_list.dart

@@ -8,6 +8,7 @@ import 'package:flutter/widgets.dart';
 class AnimatedListDemo extends StatefulWidget {
   static String routeName = '/misc/animated_list';
 
+  @override
   _AnimatedListDemoState createState() => _AnimatedListDemoState();
 }
 
@@ -17,9 +18,9 @@ class _AnimatedListDemoState extends State<AnimatedListDemo> {
 
   void addUser() {
     setState(() {
-      int index = listData.length;
+      var index = listData.length;
       listData.add(
-        UserModel(firstName: "New", lastName: "Person"),
+        UserModel(firstName: 'New', lastName: 'Person'),
       );
       _listKey.currentState
           .insertItem(index, duration: Duration(milliseconds: 300));
@@ -96,23 +97,23 @@ class UserModel {
 
 List<UserModel> initialListData = [
   UserModel(
-    firstName: "Govind",
-    lastName: "Dixit",
+    firstName: 'Govind',
+    lastName: 'Dixit',
   ),
   UserModel(
-    firstName: "Greta",
-    lastName: "Stoll",
+    firstName: 'Greta',
+    lastName: 'Stoll',
   ),
   UserModel(
-    firstName: "Monty",
-    lastName: "Carlo",
+    firstName: 'Monty',
+    lastName: 'Carlo',
   ),
   UserModel(
-    firstName: "Petey",
-    lastName: "Cruiser",
+    firstName: 'Petey',
+    lastName: 'Cruiser',
   ),
   UserModel(
-    firstName: "Barry",
-    lastName: "Cade",
+    firstName: 'Barry',
+    lastName: 'Cade',
   ),
 ];

animations/lib/src/misc/animated_positioned.dart

@@ -9,6 +9,7 @@ import 'package:flutter/material.dart';
 class AnimatedPositionedDemo extends StatefulWidget {
   static String routeName = '/basics/09_animated_positioned';
 
+  @override
   _AnimatedPositionedDemoState createState() => _AnimatedPositionedDemoState();
 }
 
@@ -20,6 +21,7 @@ class _AnimatedPositionedDemoState extends State<AnimatedPositionedDemo> {
 
   double generateLeftPosition(double left) => Random().nextDouble() * left;
 
+  @override
   void initState() {
     super.initState();
     topPosition = generateTopPosition(30);
@@ -33,6 +35,7 @@ class _AnimatedPositionedDemoState extends State<AnimatedPositionedDemo> {
     });
   }
 
+  @override
   Widget build(BuildContext context) {
     final size = MediaQuery.of(context).size;
     final appBar = AppBar();
@@ -60,7 +63,7 @@ class _AnimatedPositionedDemoState extends State<AnimatedPositionedDemo> {
                     width: 150,
                     height: 50,
                     child: Text(
-                      "Click Me",
+                      'Click Me',
                       style: TextStyle(
                         color:
                             Theme.of(context).buttonTheme.colorScheme.onPrimary,

animations/lib/src/misc/animated_switcher.dart

@@ -25,6 +25,7 @@ Widget generateContainer(int keyCount) => Container(
 class AnimatedSwitcherDemo extends StatefulWidget {
   static String routeName = '/basics/10_animated_switcher';
 
+  @override
   _AnimatedSwitcherDemoState createState() => _AnimatedSwitcherDemoState();
 }
 
@@ -32,12 +33,14 @@ class _AnimatedSwitcherDemoState extends State<AnimatedSwitcherDemo> {
   Widget container;
   int keyCount;
 
+  @override
   void initState() {
     super.initState();
     keyCount = 0;
     container = generateContainer(keyCount);
   }
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
@@ -47,7 +50,7 @@ class _AnimatedSwitcherDemoState extends State<AnimatedSwitcherDemo> {
               () => container = generateContainer(++keyCount),
             ),
             child: Text(
-              "Change Widget",
+              'Change Widget',
               style: TextStyle(
                   color: Theme.of(context).buttonTheme.colorScheme.onPrimary),
             ),

animations/lib/src/misc/card_swipe.dart

@@ -17,6 +17,7 @@ class CardSwipeDemo extends StatefulWidget {
 class _CardSwipeDemoState extends State<CardSwipeDemo> {
   List<String> fileNames;
 
+  @override
   void initState() {
     super.initState();
     _resetCards();
@@ -30,6 +31,7 @@ class _CardSwipeDemoState extends State<CardSwipeDemo> {
     ];
   }
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
@@ -79,6 +81,7 @@ class Card extends StatelessWidget {
 
   Card(this.imageAssetName);
 
+  @override
   Widget build(BuildContext context) {
     return AspectRatio(
       aspectRatio: 3 / 5,
@@ -104,6 +107,7 @@ class SwipeableCard extends StatefulWidget {
     this.imageAssetName,
   });
 
+  @override
   _SwipeableCardState createState() => _SwipeableCardState();
 }
 
@@ -114,6 +118,7 @@ class _SwipeableCardState extends State<SwipeableCard>
   double _dragStartX;
   bool _isSwipingLeft = false;
 
+  @override
   void initState() {
     super.initState();
     _controller = AnimationController.unbounded(vsync: this);
@@ -123,6 +128,7 @@ class _SwipeableCardState extends State<SwipeableCard>
     ));
   }
 
+  @override
   Widget build(BuildContext context) {
     return SlideTransition(
       position: _animation,
@@ -181,6 +187,7 @@ class _SwipeableCardState extends State<SwipeableCard>
     });
   }
 
+  @override
   void dispose() {
     _controller.dispose();
     super.dispose();

animations/lib/src/misc/carousel.dart

@@ -41,7 +41,7 @@ class CarouselDemo extends StatelessWidget {
   }
 }
 
-typedef void OnCurrentItemChangedCallback(int currentItem);
+typedef OnCurrentItemChangedCallback = void Function(int currentItem);
 
 class Carousel extends StatefulWidget {
   final IndexedWidgetBuilder itemBuilder;

animations/lib/src/misc/expand_card.dart

@@ -19,6 +19,7 @@ class ExpandCardDemo extends StatelessWidget {
 }
 
 class ExpandCard extends StatefulWidget {
+  @override
   _ExpandCardState createState() => _ExpandCardState();
 }
 

animations/lib/src/misc/focus_image.dart

@@ -7,6 +7,7 @@ import 'package:flutter/material.dart';
 class FocusImageDemo extends StatelessWidget {
   static String routeName = '/misc/focus_image';
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(title: Text('Focus Image')),
@@ -16,6 +17,7 @@ class FocusImageDemo extends StatelessWidget {
 }
 
 class Grid extends StatelessWidget {
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       body: GridView.builder(
@@ -68,6 +70,7 @@ class SmallCard extends StatelessWidget {
 
   SmallCard(this.imageAssetName);
 
+  @override
   Widget build(BuildContext context) {
     return Card(
       child: Material(
@@ -91,6 +94,7 @@ class _SecondPage extends StatelessWidget {
 
   _SecondPage(this.imageAssetName);
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       backgroundColor: Colors.black,