LinearProgressIndicator Flutter Usage

2020-07-10 10:44发布

站内文章 / Android
85 0 0

问题:

I am learning Flutter allthought i dont know if it is right decition or not. Any way i want to use LinearProgressIndicator Component from Material Librery but i didnt get how to use it i tried this code:

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,
  ),
   ));
  }
 }

but i get always this error 

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.

How to slove that and i treid to do this Demo Flutter Progress Indicator Demo but Also the same Result Any one can help me in working example about that or can tell me what is the wrong in my code ?? Regards

回答1:

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,),

        )
    );
  }

}


回答2:

You can use AlwaysStoppedAnimation simply for valueColor,

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


回答3:

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



回答4:

The Solution for this Problem was Switching the Flutter Channel from beta to master channel and then the code above worked



标签： android dart material-design flutter flutter-animation
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