我试图从 API 服务器检索我的数据并使用 flutter 将其呈现在我的移动应用程序中 .. 但出现错误
The getter 'length' was called on null
任何建议请...谢谢
我的代码是
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'dart:core';
import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:json/add.dart';
void main() => runApp(MyApp());
Future<List> getData() async {
String url = 'http://192.168.0.55:4000/api/contacts';
http.Response response = await http.get(url);
return json.decode(response.body);
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);
return MaterialApp(
routes: <String, WidgetBuilder>{
'/Add': (BuildContext context) => new Add(),
},
home: HomePage(),
);
}
}
class HomePage extends StatefulWidget {
@override
HomePageState createState() {
return new HomePageState();
}
}
class HomePageState extends State<HomePage> {
List data;
void getList() async {
this.data = (await getData());
print(data);
}
@override
void initState() {
getList();
}
Widget build(BuildContext context) {
return new Scaffold(
appBar: AppBar(
centerTitle: true,
title: new Text("Chat"),
),
body: new Center(
child: new ListView.builder(
itemCount: data.length,
itemBuilder: (BuildContext context, int position) {
return new ListTile(
title: new Text('${data[position]['name']}'),
);
}),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.person_add),
onPressed: () {
Navigator.of(context).pushNamed('/Add');
}),
);
}
}
输出控制台
Performing hot restart...
Syncing files to device Android SDK built for x86...
Restarted application in 4,410ms.
I/flutter (10119): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (10119): The following NoSuchMethodError was thrown building HomePage(dirty, state: HomePageState#80635):
I/flutter (10119): The getter 'length' was called on null.
I/flutter (10119): Receiver: null
I/flutter (10119): Tried calling: length
I/flutter (10119):
I/flutter (10119): When the exception was thrown, this was the stack:
I/flutter (10119): #0 Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
I/flutter (10119): #1 HomePageState.build (package:json/main.dart:59:29)
I/flutter (10119): #2 StatefulElement.build (package:flutter/src/widgets/framework.dart:3809:27)
I/flutter (10119): #3 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3721:15)
I/flutter (10119): #4 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #5 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #6 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #7 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #8 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #9 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #10 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #11 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #12 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #13 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #14 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #15 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #16 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #17 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #18 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #19 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #20 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #21 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #22 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #23 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #24 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #25 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #26 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #27 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #28 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #29 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #30 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #31 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #32 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #33 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #34 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #35 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #36 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #37 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #38 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #39 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #40 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #41 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #42 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #43 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #44 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #45 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #46 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #47 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #48 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #49 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #50 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #51 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #52 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #53 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #54 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #55 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #56 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #57 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #58 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #59 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #60 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #61 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #62 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #63 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #64 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #65 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #66 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #67 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #68 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #69 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #70 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #71 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #72 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #73 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #74 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #75 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #76 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #77 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #78 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #79 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #80 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #81 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #82 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #83 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #84 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #85 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #86 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #87 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #88 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #89 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #90 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #91 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #92 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #93 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #94 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #95 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #96 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #97 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #98 MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4965:32)
I/flutter (10119): #99 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #100 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #101 _TheatreElement.mount (package:flutter/src/widgets/overlay.dart:493:16)
I/flutter (10119): #102 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #103 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #104 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #105 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #106 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #107 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #108 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #109 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #110 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #111 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #112 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #113 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #114 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #115 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #116 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #117 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #118 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #119 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #120 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #121 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #122 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #123 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #124 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #125 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #126 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #127 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #128 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #163 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #164 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #165 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #166 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #167 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #168 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #169 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #170 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #171 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #172 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #173 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #174 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #175 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #176 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #177 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #178 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #179 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter (10119): #180 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #181 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #182 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #183 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #184 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #185 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #186 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #187 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #202 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #203 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #204 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #205 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #206 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #207 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #208 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #209 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #210 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #211 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #212 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #213 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #214 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #215 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #216 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #217 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #218 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #219 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #220 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #221 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #222 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #223 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #224 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #225 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #226 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #227 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #228 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #229 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #230 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #231 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #232 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #233 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #234 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #235 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #236 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter (10119): #237 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #238 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #239 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #240 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter (10119): #241 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (10119): #242 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter (10119): #243 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter (10119): #244 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (10119): #245 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (10119): #246 RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:909:16)
I/flutter (10119): #247 RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:880:5)
I/flutter (10119): #248 RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:826:17)
I/flutter (10119): #249 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2266:19)
I/flutter (10119): #250 RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:825:13)
I/flutter (10119): #251 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:712:7)
I/flutter (10119): #252 runApp (package:flutter/src/widgets/binding.dart:756:7)
I/flutter (10119): #253 main (package:json/main.dart:8:16)
I/flutter (10119): #254 _startIsolate.<anonymous closure> (dart:isolate/runtime/libisolate_patch.dart:289:19)
I/flutter (10119): #255 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)
I/flutter (10119): ════════════════════════════════════════════════════════════════════════════════════════════════════
I/flutter (10119): [{_id: 5c55e837b1dee7326c4ba39d, create_date: 2019-02-02T18:57:59.406Z, name: Tariq, gender: male, email: ta@gmail.com, phone: 07954622145, __v: 0}, {_id: 5c55e86cb1dee7326c4ba39e, create_date: 2019-02-02T18:58:52.346Z, name: He, gender: Female, email: h@gmail.com, phone: 075554622145, __v: 0}, {_id: 5c55e890b1dee7326c4ba39f, create_date: 2019-02-02T18:59:28.108Z, name: Sh, gender: Female, email: sh@gmail.com, phone: 075654622145, __v: 0}, {_id: 5c584f60af32d00dec0facae, create_date: 2019-02-04T14:42:40.036Z, name: Emad, gender: male, email: emad@gmail.com, __v: 0}, {_id: 5c585236af32d00dec0facaf, create_date: 2019-02-04T14:54:46.734Z, name: Fa, gender: Female, email: Fa@gmail.com, phone: 075654622145, __v: 0}, {_id: 5c58605bcf4f4c3008e50a04, create_date: 2019-02-04T15:55:07.696Z, name: Fa, gender: Female, email: f @gmail.com, phone: 075654622145, __v: 0}]
当我运行代码时，我在控制台中获得了数据，但在移动 APP 中获得了 UI。我得到了错误
output
最佳答案
您需要警惕data == null时的情况
body: new Center(
child: data == null ? Container() : new ListView.builder(
itemCount: data.length,
itemBuilder: (BuildContext context, int position) {
return new ListTile(
title: new Text('${data[position]['name']}'),
);
}),
),
关于dart - getter 'length' 在 null 上被调用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/54539920/