我正在学习 Flutter，虽然我不知道它是否正确。我想以任何方式使用 Material Librery 中的 LinearProgressIndicator 组件，但我不知道如何使用它我尝试了这段代码:
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;
@override
void initState() {
super.initState();
_controller = new AnimationController(
duration: const Duration(milliseconds: 1500),
vsync: this,
);
_playAnimation();
}
Future<Null> _playAnimation() async {
try {
await _controller.repeat().orCancel;
} on TickerCanceled {
// the animation got canceled, probably because we were disposed
}
}
@override
void dispose() {
_controller.stop();
super.dispose();
}
@override
Widget build(BuildContext context) {
return _buildAnimation(context, null);
}
Widget _buildAnimation(BuildContext context, Widget child) {
return new Center(
child: new Container(
color: Colors.redAccent.withOpacity(.1),
child: new LinearProgressIndicator(
value: _controller.value,
backgroundColor: Colors.redAccent,
),
));
}
}
但我总是得到这个错误
I/flutter ( 3819): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY
╞═══════════════════════════════════════════════════════════
I/flutter ( 3819): The following NoSuchMethodError was thrown building
ProgressIndicatorDemo(dirty, state:
I/flutter ( 3819): _ProgressIndicatorDemoState#80400(ticker active)):
I/flutter ( 3819): The getter 'value' was called on null.
I/flutter ( 3819): Receiver: null
I/flutter ( 3819): Tried calling: value
I/flutter ( 3819):
I/flutter ( 3819): When the exception was thrown, this was the stack:
I/flutter ( 3819): #0 Object.noSuchMethod
(dart:core/runtime/libobject_patch.dart:46:5)
I/flutter ( 3819): #1 _ProgressIndicatorDemoState.build
(file:///E:/Flutter_work/animation_test/lib/main.dart:67:26)
I/flutter ( 3819): #2 StatefulElement.build
(package:flutter/src/widgets/framework.dart:3730:27)
I/flutter ( 3819): #3 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3642:15)
I/flutter ( 3819): #4 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #5 StatefulElement.update
(package:flutter/src/widgets/framework.dart:3799:5)
I/flutter ( 3819): #6 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #7 SingleChildRenderObjectElement.update
(package:flutter/src/widgets/framework.dart:4661:14)
I/flutter ( 3819): #8 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #9 SingleChildRenderObjectElement.update
(package:flutter/src/widgets/framework.dart:4661:14)
I/flutter ( 3819): #10 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #11 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #12 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #13 StatelessElement.update
(package:flutter/src/widgets/framework.dart:3702:5)
I/flutter ( 3819): #14 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #15 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #16 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #17 ProxyElement.update
(package:flutter/src/widgets/framework.dart:3909:5)
I/flutter ( 3819): #18 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #19 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #20 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #21 ProxyElement.update
(package:flutter/src/widgets/framework.dart:3909:5)
I/flutter ( 3819): #22 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #23 RenderObjectElement.updateChildren
(package:flutter/src/widgets/framework.dart:4379:32)
I/flutter ( 3819): #24 MultiChildRenderObjectElement.update
(package:flutter/src/widgets/framework.dart:4769:17)
I/flutter ( 3819): #25 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #26 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #27 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #28 StatefulElement.update
(package:flutter/src/widgets/framework.dart:3799:5)
I/flutter ( 3819): #29 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #30 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #31 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #32 ProxyElement.update
(package:flutter/src/widgets/framework.dart:3909:5)
I/flutter ( 3819): #33 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #34 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #35 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #36 StatefulElement.update
(package:flutter/src/widgets/framework.dart:3799:5)
I/flutter ( 3819): #37 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #38 SingleChildRenderObjectElement.update
(package:flutter/src/widgets/framework.dart:4661:14)
I/flutter ( 3819): #39 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #40 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #41 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #42 StatelessElement.update
(package:flutter/src/widgets/framework.dart:3702:5)
I/flutter ( 3819): #43 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #44 SingleChildRenderObjectElement.update
(package:flutter/src/widgets/framework.dart:4661:14)
I/flutter ( 3819): #45 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #46 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #47 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #48 StatefulElement.update
(package:flutter/src/widgets/framework.dart:3799:5)
I/flutter ( 3819): #49 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #50 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #51 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #52 StatefulElement.update
(package:flutter/src/widgets/framework.dart:3799:5)
I/flutter ( 3819): #53 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #54 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #55 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #56 ProxyElement.update
(package:flutter/src/widgets/framework.dart:3909:5)
I/flutter ( 3819): #57 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #58 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #59 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #60 ProxyElement.update
(package:flutter/src/widgets/framework.dart:3909:5)
I/flutter ( 3819): #61 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #62 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #63 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #64 StatefulElement.update
(package:flutter/src/widgets/framework.dart:3799:5)
I/flutter ( 3819): #65 Element.updateChild
(package:flutter/src/widgets/framework.dart:2699:15)
I/flutter ( 3819): #66 ComponentElement.performRebuild
(package:flutter/src/widgets/framework.dart:3653:16)
I/flutter ( 3819): #67 Element.rebuild
(package:flutter/src/widgets/framework.dart:3495:5)
I/flutter ( 3819): #68 BuildOwner.buildScope
(package:flutter/src/widgets/framework.dart:2242:33)
Reloaded 0 of 391 libraries in 829ms.
Lost connection to device.
如何解决这个问题，我很想做这个演示 Flutter Progress Indicator Demo 但同样的结果任何人都可以帮助我解决这个问题，或者可以告诉我我的代码有什么问题？ 问候
最佳答案
您可以使用 AlwaysStoppedAnimation只为 valueColor,
LinearProgressIndicator(
backgroundColor: Colors.red,
valueColor: AlwaysStoppedAnimation<Color>(Colors.amber,),
value: 0.8,
),
关于android - LinearProgressIndicator flutter 使用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/51954097/