Dart 吸气剂'；长度'；被调用为空_Dart

Dart 吸气剂'；长度'；被调用为空

dart

Dart 吸气剂'；长度'；被调用为空,dart,Dart,我正在尝试从API服务器检索数据，并使用Flatter将其显示在我的移动应用程序中。。但我犯了个错误对null调用了getter“length” 有什么建议吗。。。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

我正在尝试从API服务器检索数据，并使用Flatter将其显示在我的移动应用程序中。。但我犯了个错误

对null调用了getter“length”

有什么建议吗。。。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');
          }),
    );
  }
}

导入“包装：颤振/材料.省道”；
导入“包：flifter/services.dart”；
导入“省道：核心”；
导入“dart:convert”；
将“package:http/http.dart”导入为http；
导入“package:json/add.dart”；
void main（）=>runApp（MyApp（））；
Future getData（）异步{
字符串url='0http://192.168.0.55:4000/api/contacts';
http.Response-Response=等待http.get（url）；
返回json.decode（response.body）；
}
类MyApp扩展了无状态小部件{
@凌驾
小部件构建（构建上下文）{
SystemChrome.setPreferredOrientations（[DeviceOrientation.GraphicUp]）；
返回材料PP(
路线：{
“/Add”：（BuildContext）=>new Add（），
},
主页：主页（），
);
}
}
类主页扩展了StatefulWidget{
@凌驾
HomePageState createState（）{
返回新的HomePageState（）；
}
}
类HomePageState扩展了状态{
列出数据；
void getList（）异步{
this.data=（wait getData（））；
打印（数据）；
}
@凌驾
void initState（）{
getList（）；
}
小部件构建（构建上下文）{
归还新脚手架(
appBar:appBar(
标题：对，
标题：新文本（“聊天”），
),
正文：新中心(
子项：新建ListView.builder(
itemCount:data.length，
itemBuilder：（构建上下文，int位置）{
返回新的ListTile(
标题：新文本（“${data[position]['name']}”），
);
}),
),
浮动操作按钮：浮动操作按钮(
子：图标（Icons.person\u add），
已按下：（）{
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}]

正在执行热重启。。。正在将文件同步到为x86构建的Android SDK设备。。。在4410ms内重新启动应用程序。 I/颤振（10119）：══╡ WIDGETS库捕获到异常╞═══════════════════════════════════════════════════════════ I/flatter（10119）：在构建主页时抛出以下NoSuchMethodError（脏，状态：HomePageState#80635）： I/flatter（10119）：getter“length”被调用为null。 I/颤振（10119）：接收器：空 I/颤振（10119）：尝试呼叫：长度 I/颤振（10119）： I/flatter（10119）：当抛出异常时，这是堆栈： I/flatter（10119）：#0 Object.noSuchMethod（dart:core/runtime/libobject_patch.dart:50:5） I/flatter（10119）：#1 HomePageState.build（包：json/main.dart:59:29） I/flatter（10119）：#2 StatefulElement.build（包：flatter/src/widgets/framework.dart:3809:27） I/flatter（10119）：#3 ComponentElement.performRebuild（包：flatter/src/widgets/framework.dart:3721:15） I/flatter（10119）：#4 Element.rebuild（包：flatter/src/widgets/framework.dart:3547:5） I/flatter（10119）：#5个组件元素。firstBuild（包：flatter/src/widgets/framework.dart:3701:5） I/flatter（10119）：#6 StatefulElement._firstBuild（包：flatter/src/widgets/framework.dart:3848:11） I/flatter（10119）：#7 ComponentElement.mount（包：flatter/src/widgets/framework.dart:3696:5） I/flatter（10119）：#8 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#9 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#10 SingleChildRenderObjectElement.mount（包：flatter/src/widgets/framework.dart:4860:14） I/flatter（10119）：#11 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#12 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#13 ComponentElement.performRebuild（包：flatter/src/widgets/framework.dart:3732:16） I/flatter（10119）：#14 Element.rebuild（包：flatter/src/widgets/framework.dart:3547:5） I/flatter（10119）：#15 ComponentElement._firstBuild（包：flatter/src/widgets/framework.dart:3701:5） I/flatter（10119）：#16 ComponentElement.mount（包：flatter/src/widgets/framework.dart:3696:5） I/flatter（10119）：#17 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#18 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#19 SingleChildRenderObjectElement.mount（包：flatter/src/widgets/framework.dart:4860:14） I/flatter（10119）：#20 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#21 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#22 SingleChildRenderObjectElement.mount（包：flatter/src/widgets/framework.dart:4860:14） I/flatter（10119）：#23 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#24 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#25 SingleChildRenderObjectElement.mount（包：flatter/src/widgets/framework.dart:4860:14） I/flatter（10119）：#26 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#27 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#28 SingleChildRenderObjectElement.mount（包：flatter/src/widgets/framework.dart:4860:14） I/flatter（10119）：#29 Element.inflateWidget（包：flatter/src/widgets/framework.dart:2950:14） I/flatter（10119）：#30 Element.updateChild（包：flatter/src/widgets/framework.dart:2753:12） I/flatter（10119）：#31 ComponentElement.performRebuild（包：flatter/src/widgets/framework.dart:3732:16）我/

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

List _elements = [];

list data;