Dart I'；我试图在按下时设置setState（）中的变量，但我'；我犯了一个错误
这是变量初始化Dart I'；我试图在按下时设置setState（）中的变量，但我'；我犯了一个错误,dart,flutter,Dart,Flutter,这是变量初始化 var displayResult = ''; 这是新闻代码 Padding( padding: EdgeInsets.all(5.0), child: Row( children: <Widget>[ Expanded( child: RaisedButton(
var displayResult = '';
Padding(
padding: EdgeInsets.all(5.0),
child: Row(
children: <Widget>[
Expanded(
child: RaisedButton(
color: Theme
.of(context)
.primaryColor,
textColor: Theme
.of(context)
.primaryColorLight,
child: Text("calculate"),
onPressed: () {
setState(() {
this.displayResult = _calculateTotalReturn();
});
},
)),
Performing hot reload...
Syncing files to device iPhone XR...
flutter: ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
flutter: The following assertion was thrown building SIForm(dirty, dependencies:
flutter: [_LocalizationsScope-[GlobalKey#4c1f9], _InheritedTheme], state: _SIFormState#b2966):
flutter: 'package:flutter/src/widgets/text.dart': Failed assertion: line 237 pos 15: 'data != null': is not
flutter: true.
flutter:
flutter: Either the assertion indicates an error in the framework itself, or we should provide substantially
flutter: more information in this error message to help you determine and fix the underlying cause.
flutter: In either case, please report this assertion by filing a bug on GitHub:
flutter: https://github.com/flutter/flutter/issues/new?template=BUG.md
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #2 new Text (package:flutter/src/widgets/text.dart:237:15)
flutter: #3 _SIFormState.build (package:simple_cal/main.dart:153:24)
flutter: #4 StatefulElement.build (package:flutter/src/widgets/framework.dart:3825:27)
flutter: #5 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3736:15)
flutter: #6 Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
flutter: #7 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2273:33)
flutter: #8 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:700:20)
flutter: #9 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:268:5)
flutter: #10 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:988:15)
flutter: #11 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:928:9)
flutter: #12 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame.<anonymous closure> (package:flutter/src/scheduler/binding.dart:749:7)
flutter: #14 _Timer._runTimers (dart:isolate/runtime/libtimer_impl.dart:382:19)
flutter: #15 _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:416:5)
flutter: #16 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
flutter: (elided 3 frames from class _AssertionError and package dart:async)
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
Reloaded 1 of 432 libraries in 641ms.
正在执行热重新加载。。。
正在将文件同步到设备iPhone XR。。。
颤振：══╡ WIDGETS库捕获到异常╞═══════════════════════════════════════════════════════════
颤振：在构建SIForm时抛出以下断言（脏的，依赖项：
颤振：[[u本地化范围-[GlobalKey#4c1f9]，[u继承主题]，状态：[u SIFormState#b2966]：
颤振：“包：颤振/src/widgets/text.dart”：失败的断言：第237行第15位：“数据！”null”：不是
弗利特：是的。
颤振：
颤振：要么断言表明框架本身存在错误，要么我们应该提供
颤振：此错误消息中的更多信息可帮助您确定并修复根本原因。
颤振：无论哪种情况，请在GitHub上提交一个bug来报告这一断言：
颤振：https://github.com/flutter/flutter/issues/new?template=BUG.md
颤振：
颤振：抛出异常时，这是堆栈：
颤振：2个新文本（包：颤振/src/widgets/Text.dart:237:15）
颤振：#3#SIFormState.build（包：simple#u-cal/main.dart:153:24）
flatter:#4 StatefulElement.build（包：flatter/src/widgets/framework.dart:3825:27）
flatter:#5 ComponentElement.performRebuild（包：flatter/src/widgets/framework.dart:3736:15）
flatter:#6 Element.rebuild（包：flatter/src/widgets/framework.dart:3559:5）
flatter:#7buildowner.buildScope（包：flatter/src/widgets/framework.dart:2273:33）
颤振：8#u WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&ScheduleBinding&PaintingBinding&SemanticsBinding&RenderBinding&WidgetsBinding.drawFrame（包：颤振/src/widgets/binding.dart:700:20）
flatter:#9"WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&ScheduleBinding&PaintingBinding&SemanticsBinding&RenderBinding."handlePersistentFrameCallback（包：flatter/src/rendering/binding.dart:268:5）
flatter:#10 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback（包：flatter/src/scheduler/binding.dart:988:15）
颤振：11#u WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame（包：颤振/src/scheduler/binding.dart:928:9）
颤振：#12#WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.scheduleWarmUpFrame。（包：颤振/src/scheduler/binding.dart:749:7）
颤振：14计时器。运行计时器（dart:isolate/runtime/libtimer\u impl.dart:382:19）
颤振：#15#计时器。handleMessage（dart:isolate/runtime/libtimer_impl.dart:416:5）
颤振：#16 RawReceivePortImpl.handleMessage（dart:isolate/runtime/libisolate_patch.dart:171:12）
颤振：（从类断言错误和包dart中删除3帧：异步）
颤振：════════════════════════════════════════════════════════════════════════════════════════════════════
在641ms内重新加载432个库中的1个。
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
Widget MyApp() {
return MaterialApp(
title: 'Simple Intrest app',
home: SIForm (),
theme: ThemeData(
primaryColor: Colors.deepPurple,
accentColor: Colors.deepPurpleAccent
),
);
}
class SIForm extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _SIFormState ();
}
}
class _SIFormState extends State<SIForm> {
var _currencies = ["INR", "USD", "CAD"];
var _currentItemSelected = "INR";
var displayResult = '';
TextEditingController principleController = TextEditingController();
TextEditingController roiController = TextEditingController();
TextEditingController termController = TextEditingController();
@override
Widget build(BuildContext context) {
TextStyle textStyle = Theme
.of(context)
.textTheme
.title;
return Scaffold(
appBar: AppBar(
title: Text("Simple Interest Calc"),
),
body: Container(padding: EdgeInsets.only(top: 50.0),
child: ListView(
children: <Widget>[
Padding(
padding: EdgeInsets.all(5.0),
child: TextField(
keyboardType: TextInputType.number,
controller: principleController,
decoration: InputDecoration(
labelText: 'principle',
hintText: '0.00',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(5.0)
)
),
)),
Padding(
padding: EdgeInsets.all(5.0),
child: TextField(
controller: roiController,
keyboardType: TextInputType.number,
decoration: InputDecoration(
labelText: 'Rate of Interest',
hintText: '0.00',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(5.0)
)
),
)),
Padding(
padding: EdgeInsets.all(5.0),
child: Row(
children: <Widget>[
Expanded(child: TextField(
controller: termController,
keyboardType: TextInputType.number,
decoration: InputDecoration(
labelText: 'Terms',
hintText: '%',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(5.0)
)
),
)),
Container(width: 10.0),
Expanded(
child: DropdownButton<String>(
items: _currencies.map((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
value: _currentItemSelected,
onChanged: (val) {
_ondropDownChange(val);
},),
),
],
)),
Padding(
padding: EdgeInsets.all(5.0),
child: Row(
children: <Widget>[
Expanded(
child: RaisedButton(
color: Theme
.of(context)
.primaryColor,
textColor: Theme
.of(context)
.primaryColorLight,
child: Text("calculate"),
onPressed: () {
setState(() {
this.displayResult = _calculateTotalReturn();
});
},
)),
Container(width: 5.0),
Expanded(
child: RaisedButton(
color: Theme
.of(context)
.accentColor,
textColor: Theme
.of(context)
.primaryColorLight,
child: Text("Reset"),
onPressed: () {
setState(() {
// _reset();
});
}
)),
],
)),
Padding(
padding: EdgeInsets.all(5.0),
child: Text(this.displayResult),
)
],
),
),
);
}
void _ondropDownChange(String value) {
setState(() {
this._currentItemSelected = value;
});
}
String _calculateTotalReturn() {
setState(() {
double principle = double.parse(principleController.text);
double roi = double.parse(roiController.text);
double term = double.parse(termController.text);
double tap = principle + (principle * roi * term) / 100;
String result = "After $term years, your investment will worth $tap $_currentItemSelected";
return result;
});
}
void _reset() {
setState(() {
this.principleController.text = " ";
this.roiController.text = " ";
this.termController.text = " ";
this.displayResult = " ";
});
}
}
导入“包装：颤振/材料.省道”；
void main（）=>runApp（MyApp（））；
Widget MyApp（）{
返回材料PP(
标题：“简单Intrest应用程序”，
主页：SIForm（），
主题：主题数据(
原色：颜色。深紫色，
accentColor:颜色。深紫色
),
);
}
类SIForm扩展StatefulWidget{
@凌驾
状态createState（）{
返回_SIFormState（）；
}
}
类_SIFormState扩展状态{
风险值货币=[“印度卢比”、“美元”、“加元”]；
var\u currentItemSelected=“INR”；
var displayResult=''；
TextEditingController principleController=TextEditingController（）；
TextEditingController=TextEditingController（）；
TextEditingController termController=TextEditingController（）；
@凌驾
小部件构建（构建上下文）{
text样式text样式=主题
.of（上下文）
.文本主题
标题
返回脚手架(
appBar:appBar(
标题：文本（“单利计算”），
),
车身：容器（衬垫：仅限边缘套件（顶部：50.0），
子：ListView(
儿童：[
填充物(
填充：所有边缘设置（5.0），
孩子：TextField(
键盘类型：TextInputType.number，
控制器：主控制器，
装饰：输入装饰(
labelText:“原则”，
hintText:'0.00'，
边框：大纲输入边框(
边界半径：边界半径。圆形（5.0）
)
),
)),
填充物(
填充：所有边缘设置（5.0），
孩子：TextField(
控制器：控制器，
键盘类型：TextInputType.number，
装饰：输入装饰(
labelText:“利率”，
hintText:'0.00'，
边框：大纲输入边框(
边界半径：边界半径。圆形（5.0）
)
),
)),
填充物(
填充：所有边缘设置（5.0），
孩子：排(
儿童：[
已展开（子项：TextField(
控制器：终端控制器，
键盘类型：TextInputType.number，
装饰：输入装饰(
labelText:“术语”，
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
Widget MyApp() {
return MaterialApp(
title: 'Simple Intrest app',
home: SIForm (),
theme: ThemeData(
primaryColor: Colors.deepPurple,
accentColor: Colors.deepPurpleAccent
),
);
}
class SIForm extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _SIFormState ();
}
}
class _SIFormState extends State<SIForm> {
var _currencies = ["INR", "USD", "CAD"];
var _currentItemSelected = "INR";
var displayResult = '';
TextEditingController principleController = TextEditingController();
TextEditingController roiController = TextEditingController();
TextEditingController termController = TextEditingController();
@override
Widget build(BuildContext context) {
TextStyle textStyle = Theme
.of(context)
.textTheme
.title;
return Scaffold(
appBar: AppBar(
title: Text("Simple Interest Calc"),
),
body: Container(padding: EdgeInsets.only(top: 50.0),
child: ListView(
children: <Widget>[
Padding(
padding: EdgeInsets.all(5.0),
child: TextField(
keyboardType: TextInputType.number,
controller: principleController,
decoration: InputDecoration(
labelText: 'principle',
hintText: '0.00',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(5.0)
)
),
)),
Padding(
padding: EdgeInsets.all(5.0),
child: TextField(
controller: roiController,
keyboardType: TextInputType.number,
decoration: InputDecoration(
labelText: 'Rate of Interest',
hintText: '0.00',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(5.0)
)
),
)),
Padding(
padding: EdgeInsets.all(5.0),
child: Row(
children: <Widget>[
Expanded(child: TextField(
controller: termController,
keyboardType: TextInputType.number,
decoration: InputDecoration(
labelText: 'Terms',
hintText: '%',
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(5.0)
)
),
)),
Container(width: 10.0),
Expanded(
child: DropdownButton<String>(
items: _currencies.map((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
value: _currentItemSelected,
onChanged: (val) {
_ondropDownChange(val);
},),
),
],
)),
Padding(
padding: EdgeInsets.all(5.0),
child: Row(
children: <Widget>[
Expanded(
child: RaisedButton(
color: Theme
.of(context)
.primaryColor,
textColor: Theme
.of(context)
.primaryColorLight,
child: Text("calculate"),
onPressed: () {
setState(() {
this.displayResult = _calculateTotalReturn();
});
},
)),
Container(width: 5.0),
Expanded(
child: RaisedButton(
color: Theme
.of(context)
.accentColor,
textColor: Theme
.of(context)
.primaryColorLight,
child: Text("Reset"),
onPressed: () {
setState(() {
// _reset();
});
}
)),
],
)),
Padding(
padding: EdgeInsets.all(5.0),
child: Text(this.displayResult),
)
],
),
),
);
}
void _ondropDownChange(String value) {
setState(() {
this._currentItemSelected = value;
});
}
String _calculateTotalReturn() {
setState(() {
double principle = double.parse(principleController.text);
double roi = double.parse(roiController.text);
double term = double.parse(termController.text);
double tap = principle + (principle * roi * term) / 100;
String result = "After $term years, your investment will worth $tap $_currentItemSelected";
return result;
});
}
void _reset() {
setState(() {
this.principleController.text = " ";
this.roiController.text = " ";
this.termController.text = " ";
this.displayResult = " ";
});
}
}