LinearProgressIndicator Flutter Usage

You can use AlwaysStoppedAnimation simply for valueColor,

LinearProgressIndicator(    backgroundColor: Colors.red,    valueColor: AlwaysStoppedAnimation<Color>(Colors.amber,),    value: 0.8,),

You are not using animation object.

import 'dart:async';import 'package:flutter/material.dart';void main() {  runApp(new MaterialApp(    debugShowCheckedModeBanner: false,    home: new MyApp(),  ));}class MyApp extends StatefulWidget {  @override  MyAppState createState() => new MyAppState();}class MyAppState extends State<MyApp> {  @override  Widget build(BuildContext context) {    return new Scaffold(      appBar: new AppBar(        title: new Text('Slider Demo'),      ),      body: new Container(        color: Colors.blueAccent,        padding: new EdgeInsets.all(32.0),        child: new ProgressIndicatorDemo(),      ),    );  }}class ProgressIndicatorDemo extends StatefulWidget {  @override  _ProgressIndicatorDemoState createState() =>      new _ProgressIndicatorDemoState();}class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo>    with SingleTickerProviderStateMixin {  AnimationController controller;  Animation<double> animation;  @override  void initState() {    super.initState();    controller = AnimationController(        duration: const Duration(milliseconds: 2000), vsync: this);    animation = Tween(begin: 0.0, end: 1.0).animate(controller)      ..addListener(() {        setState(() {          // the state that has changed here is the animation object’s value        });      });    controller.repeat();  }  @override  void dispose() {    controller.stop();    super.dispose();  }  @override  Widget build(BuildContext context) {    return new Center(        child: new Container(          child:  LinearProgressIndicator( value:  animation.value,),        )    );  }}

Try this :

Instead of

value: _controller.value,

Use

value: _controller.value ?? 0.0,

You can also use the package that I created , it has animation:

https://pub.dartlang.org/packages/percent_indicator