Samples maintenance (#435)

animations/lib/src/basics/01_animated_container.dart

@@ -13,6 +13,7 @@ Color generateColor() => Color(0xFFFFFFFF & Random().nextInt(0xFFFFFFFF));
 class AnimatedContainerDemo extends StatefulWidget {
   static String routeName = '/basics/01_animated_container';
 
+  @override
   _AnimatedContainerDemoState createState() => _AnimatedContainerDemoState();
 }
 
@@ -21,6 +22,7 @@ class _AnimatedContainerDemoState extends State<AnimatedContainerDemo> {
   double borderRadius;
   double margin;
 
+  @override
   void initState() {
     super.initState();
     color = Colors.deepPurple;
@@ -36,6 +38,7 @@ class _AnimatedContainerDemoState extends State<AnimatedContainerDemo> {
     });
   }
 
+  @override
   Widget build(BuildContext context) {
     // This widget is built using an AnimatedContainer, one of the easiest to use
     // animated Widgets. Whenever the AnimatedContainer's properties, such as decoration,

animations/lib/src/basics/02_page_route_builder.dart

@@ -7,6 +7,7 @@ import 'package:flutter/material.dart';
 class PageRouteBuilderDemo extends StatelessWidget {
   static const String routeName = '/basics/page_route_builder';
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(),
@@ -38,6 +39,7 @@ Route _createRoute() {
 }
 
 class _Page2 extends StatelessWidget {
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(),

animations/lib/src/basics/04_tweens.dart

@@ -7,6 +7,7 @@ import 'package:flutter/material.dart';
 class TweenDemo extends StatefulWidget {
   static const String routeName = '/basics/tweens';
 
+  @override
   _TweenDemoState createState() => _TweenDemoState();
 }
 
@@ -17,6 +18,7 @@ class _TweenDemoState extends State<TweenDemo>
   AnimationController controller;
   Animation<double> animation;
 
+  @override
   void initState() {
     super.initState();
 
@@ -28,11 +30,13 @@ class _TweenDemoState extends State<TweenDemo>
     animation = Tween(begin: 0.0, end: accountBalance).animate(controller);
   }
 
+  @override
   void dispose() {
     controller.dispose();
     super.dispose();
   }
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(),

animations/lib/src/basics/05_animated_builder.dart

@@ -7,6 +7,7 @@ import 'package:flutter/material.dart';
 class AnimatedBuilderDemo extends StatefulWidget {
   static const String routeName = '/basics/animated_builder';
 
+  @override
   _AnimatedBuilderDemoState createState() => _AnimatedBuilderDemoState();
 }
 
@@ -18,6 +19,7 @@ class _AnimatedBuilderDemoState extends State<AnimatedBuilderDemo>
   AnimationController controller;
   Animation<Color> animation;
 
+  @override
   void initState() {
     super.initState();
 
@@ -26,11 +28,13 @@ class _AnimatedBuilderDemoState extends State<AnimatedBuilderDemo>
         ColorTween(begin: beginColor, end: endColor).animate(controller);
   }
 
+  @override
   void dispose() {
     controller.dispose();
     super.dispose();
   }
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(),

animations/lib/src/basics/06_custom_tween.dart

@@ -8,6 +8,7 @@ class TypewriterTween extends Tween<String> {
   TypewriterTween({String begin = '', String end})
       : super(begin: begin, end: end);
 
+  @override
   String lerp(double t) {
     var cutoff = (end.length * t).round();
     return end.substring(0, cutoff);
@@ -17,6 +18,7 @@ class TypewriterTween extends Tween<String> {
 class CustomTweenDemo extends StatefulWidget {
   static const String routeName = '/basics/custom_tweens';
 
+  @override
   _CustomTweenDemoState createState() => _CustomTweenDemoState();
 }
 
@@ -27,6 +29,7 @@ class _CustomTweenDemoState extends State<CustomTweenDemo>
   AnimationController controller;
   Animation<String> animation;
 
+  @override
   void initState() {
     super.initState();
 
@@ -34,11 +37,13 @@ class _CustomTweenDemoState extends State<CustomTweenDemo>
     animation = TypewriterTween(end: message).animate(controller);
   }
 
+  @override
   void dispose() {
     controller.dispose();
     super.dispose();
   }
 
+  @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(

animations/lib/src/basics/07_tween_sequence.dart

@@ -27,6 +27,7 @@ class _TweenSequenceDemoState extends State<TweenSequenceDemo>
     Colors.purple,
   ];
 
+  @override
   void initState() {
     super.initState();
 
@@ -49,6 +50,7 @@ class _TweenSequenceDemoState extends State<TweenSequenceDemo>
     animation = TweenSequence<Color>(sequenceItems).animate(controller);
   }
 
+  @override
   void dispose() {
     controller.dispose();
     super.dispose();