dart - getter 'length' 在 null 上被调用

Question

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

Answer 1

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']}'),
          );
        }),
  ),