这是我在 IDE 上的错误日志。
Restarted application in 1,172ms. I/flutter (24036): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter (24036): The following NoSuchMethodError was thrown building FutureBuilder<String>(dirty, state: I/flutter (24036): _FutureBuilderState<String>#bf7da): I/flutter (24036): The getter 'length' was called on null. I/flutter (24036): Receiver: null I/flutter (24036): Tried calling: length I/flutter (24036): I/flutter (24036): The relevant error-causing widget was: [38;5;248mI/flutter (24036): FutureBuilder<String>[39;49m I/flutter (24036): I/flutter (24036): When the exception was thrown, this was the stack: [38;5;244mI/flutter (24036): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)[39;49m [38;5;248mI/flutter (24036): #1 _JsonDataState.build.<anonymous closure>[39;49m [38;5;244mI/flutter (24036): #2 _FutureBuilderState.build[39;49m [38;5;244mI/flutter (24036): #3 StatefulElement.build[39;49m [38;5;244mI/flutter (24036): #4 ComponentElement.performRebuild[39;49m [38;5;244mI/flutter (24036): #5 StatefulElement.performRebuild[39;49m [38;5;244mI/flutter (24036): #6 Element.rebuild[39;49m [38;5;244mI/flutter (24036): #7 ComponentElement._firstBuild[39;49m [38;5;244mI/flutter (24036): #8 StatefulElement._firstBuild[39;49m [38;5;244mI/flutter (24036): #9 ComponentElement.mount[39;49m I/flutter (24036): ... Normal element mounting (22 frames) [38;5;244mI/flutter (24036): #31 Element.inflateWidget[39;49m [38;5;244mI/flutter (24036): #32 MultiChildRenderObjectElement.mount[39;49m I/flutter (24036): ... Normal element mounting (193 frames) [38;5;244mI/flutter (24036): #225 Element.inflateWidget[39;49m [38;5;244mI/flutter (24036): #226 MultiChildRenderObjectElement.mount[39;49m I/flutter (24036): ... Normal element mounting (253 frames) [38;5;244mI/flutter (24036): #479 Element.inflateWidget[39;49m [38;5;244mI/flutter (24036): #480 Element.updateChild[39;49m [38;5;244mI/flutter (24036): #481 RenderObjectToWidgetElement._rebuild[39;49m [38;5;244mI/flutter (24036): #482 RenderObjectToWidgetElement.mount[39;49m [38;5;244mI/flutter (24036): #483 RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous闭包>[39;49m [38;5;244mI/flutter (24036): #484 BuildOwner.buildScope[39;49m [38;5;244mI/flutter (24036): #485 RenderObjectToWidgetAdapter.attachToRenderTree[39;49m [38] ;5;244mI/flutter (24036): #486 WidgetsBinding.attachRootWidget[39;49m [38;5;244mI/flutter (24036): #487 WidgetsBinding.scheduleAttachRootWidget.[39;49m I/flutter (24036): (省略来自 _RawReceivePortImpl 类、_Timer 类、dart:async 和 dart:async-patch 的 11 帧 I/flutter (24036)：I/flutter (24036)：════════════════ ══════════════════════════════════════════════════ ══════════════════════════════════
[38;5;248m════════ Exception caught by widgets library ═══════════════════════════════════[39;49m [38;5;244mThe following NoSuchMethodError was thrown building FutureBuilder<String>(dirty, state:_FutureBuilderState#bf7da):[39;49m 在 null 上调用了 getter 'length'。接收方：null 尝试调用：长度
[38;5;244mThe relevant error-causing widget was[39;49m [38;5;248mFutureBuilder<String>[39;49m [38;5;244mWhen the exception was thrown, this was the stack[39;49m [38;5;244m#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)[39;49m [38;5;248m#1 _JsonDataState.build.<anonymous closure>[39;49m [38;5;244m#2 _FutureBuilderState.build[39;49m [38;5;244m#3 StatefulElement.build[39;49m [38;5;244m#4 ComponentElement.performRebuild[39;49m [38;5;244m...[39;49m [38;5;248m════════════════════════════════════════════════════════════════════════════════[39;49m
这是运行的代码。该应用程序正在运行，但在启动时出现错误和红屏几秒钟。
`import 'dart:convert';
import 'package:flutter/material.dart';
class JsonData extends StatefulWidget {
@override
_JsonDataState createState() => _JsonDataState();
}
class _JsonDataState extends State<JsonData> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Home Page Data Visualization'),
),
body: Center(
child: FutureBuilder(
builder: (context, snapshot) {
var myData = json.decode(snapshot.data.toString());
return ListView.builder(
itemBuilder: (BuildContext context, int index) {
return Card(
child: ListTile(
leading: CircleAvatar(
child: Text(myData[index]['trade_code'][0])),
title: Text(myData[index]['trade_code']),
subtitle: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Text(
"\nHigh:" + myData[index]['high'],
style: TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
Text(
"Low:" + myData[index]['low'],
style: TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
Text(
"Open:" + myData[index]['open'],
style: TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
Text(
"Close:" + myData[index]['close'],
style: TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
Text(
"Volume:" + myData[index]['volume'],
style: TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.left,
),
Text(
"\nDate:" + myData[index]['date'],
style: TextStyle(fontWeight: FontWeight.bold),
textAlign: TextAlign.center,
),
],
),
isThreeLine: true,
),
elevation: 3,
);
},
itemCount: myData.length,
);
},
future: DefaultAssetBundle.of(context)
.loadString("assets/stock_market_data.json")),
),
);
}
}
`