getter 'classification' was called on null

Question

I'm about two weeks old into flutter and I don't understand what the error really means. I'll add the stack below:

List<DropdownMenuItem> showDropdownMenus() {
return CLASSIFICATION.map((item){
  return DropdownMenuItem(
    value: item,
    child: Text(item),
  );
}).toList();

}

The error stack:

I/flutter ( 4403): I/flutter ( 4403): I/flutter ( 4403): I/flutter ( 4403): Receiver: null I/flutter ( 4403): I/flutter ( 4403): I/flutter ( 4403): I/flutter ( 4403): #0 I/flutter ( 4403): #1 I/flutter ( 4403): #2 I/flutter ( 4403): #3 I/flutter ( 4403): #4 I/flutter ( 4403): #5 I/flutter ( 4403): #6 I/flutter ( 4403): #7 I/flutter ( 4403): #8 I/flutter ( 4403): #9 I/flutter ( 4403): #10 I/flutter ( 4403): #11 I/flutter ( 4403): #12 I/flutter ( 4403): #13 I/flutter ( 4403): #14 I/flutter ( 4403): #15 I/flutter ( 4403): #16 I/flutter ( 4403): #17 I/flutter ( 4403): #18 I/flutter ( 4403): #19 I/flutter ( 4403): #20 I/flutter ( 4403): #21 I/flutter ( 4403): #22 I/flutter ( 4403): #23 I/flutter ( 4403): #24 I/flutter ( 4403): #25 I/flutter ( 4403): #26 I/flutter ( 4403): #27 I/flutter ( 4403): #28 I/flutter ( 4403): #29 I/flutter ( 4403): #30 I/flutter ( 4403): #31 I/flutter ( 4403): #32 I/flutter ( 4403): #33 I/flutter ( 4403): #34 I/flutter ( 4403): #35 I/flutter ( 4403): #36 I/flutter ( 4403): #37 I/flutter ( 4403): #38 I/flutter ( 4403): #39 I/flutter ( 4403): #40 I/flutter ( 4403): #41 I/flutter ( 4403): #42 I/flutter ( 4403): #43 I/flutter ( 4403): #44 I/flutter ( 4403): #45 I/flutter ( 4403): #46 I/flutter ( 4403): #47 I/flutter ( 4403): #48 I/flutter ( 4403): #49 I/flutter ( 4403): #50 I/flutter ( 4403): #51 I/flutter ( 4403): #52 I/flutter ( 4403): #53 I/flutter ( 4403): #54 I/flutter ( 4403): #55 I/flutter ( 4403): #56 I/flutter ( 4403): #57 I/flutter ( 4403): #58 I/flutter ( 4403): #59 I/flutter ( 4403): #60 I/flutter ( 4403): #61 I/flutter ( 4403): #62 I/flutter ( 4403): #63 I/flutter ( 4403): #64 I/flutter ( 4403): #65 I/flutter ( 4403): #66 I/flutter ( 4403): #67 I/flutter ( 4403): #68 I/flutter ( 4403): #69 I/flutter ( 4403): #70 I/flutter ( 4403): #71 I/flutter ( 4403): #72 I/flutter ( 4403): #73 I/flutter ( 4403): #74 I/flutter ( 4403): #75 I/flutter ( 4403): #76 I/flutter ( 4403): #77 I/flutter ( 4403): #78 I/flutter ( 4403): #79 I/flutter ( 4403): #80 I/flutter ( 4403): #81 I/flutter ( 4403): #82 I/flutter ( 4403): #83 I/flutter ( 4403): #84 I/flutter ( 4403): #85 I/flutter ( 4403): #86 I/flutter ( 4403): #87 I/flutter ( 4403): #88 I/flutter ( 4403): #89 I/flutter ( 4403): #90 I/flutter ( 4403): #91 I/flutter ( 4403): #92 I/flutter ( 4403): #93 I/flutter ( 4403): #94 I/flutter ( 4403): #95 I/flutter ( 4403): #96 I/flutter ( 4403): #97 I/flutter ( 4403): #98 I/flutter ( 4403): #99 I/flutter ( 4403): #100 I/flutter ( 4403): #101 I/flutter ( 4403): #102 I/flutter ( 4403): #103 I/flutter ( 4403): #104 I/flutter ( 4403): #105 I/flutter ( 4403): #106 I/flutter ( 4403): #107 I/flutter ( 4403): #108 I/flutter ( 4403): #109 I/flutter ( 4403): #110 I/flutter ( 4403): #111 I/flutter ( 4403): #112 I/flutter ( 4403): #113 I/flutter ( 4403): #114 I/flutter ( 4403): #115 I/flutter ( 4403): #116 I/flutter ( 4403): #117 I/flutter ( 4403): #118 I/flutter ( 4403): #119 I/flutter ( 4403): #120 I/flutter ( 4403): #121 I/flutter ( 4403): #122 I/flutter ( 4403): #123 I/flutter ( 4403): #124 I/flutter ( 4403): #125 I/flutter ( 4403): #126 I/flutter ( 4403): #127 I/flutter ( 4403): #128 I/flutter ( 4403): #129 I/flutter ( 4403): #130 I/flutter ( 4403): #134 I/flutter ( 4403): #135 I/flutter ( 4403): The following NoSuchMethodError was thrown building RegistrationPage(dirty, state: RegistrationPageState#21643): The getter 'classification' was called on null. Tried calling: classification When the exception was thrown, this was the stack: Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5) RegistrationPageState.build (package:lesson2/view/registrationpage.dart:99:44) StatefulElement.build (package:flutter/src/widgets/framework.dart:4012:27) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3924:15) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5092:14) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3907:5) StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4053:11) ComponentElement.mount (package:flutter/src/widgets/framework.dart:3902:5) Element.inflateWidget (package:flutter/src/widgets/framework.dart:3084:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2887:12) RenderObjectElement.updateChildren (package:flutter/src/widgets/framework.dart:4875:32) MultiChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:5208:17) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) _TheatreElement.update (package:flutter/src/widgets/overlay.dart:607:16) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) StatefulElement.update (package:flutter/src/widgets/framework.dart:4085:5) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) ProxyElement.update (package:flutter/src/widgets/framework.dart:4219:5) _InheritedNotifierElement.update (package:flutter/src/widgets/inherited_notifier.dart:94:11) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:5099:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) StatefulElement.update (package:flutter/src/widgets/framework.dart:4085:5) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:5099:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) SingleChildRenderObjectElement.update (package:flutter/src/widgets/framework.dart:5099:14) Element.updateChild (package:flutter/src/widgets/framework.dart:2876:15) ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3935:16) Element.rebuild (package:flutter/src/widgets/framework.dart:3721:5) BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2340:33) _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:700:20) _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:285:5) _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1016:15) _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:958:9) _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:874:5) _invoke (dart:ui/hooks.dart:236:10) _drawFrame (dart:ui/hooks.dart:194:3) (elided 3 frames from package dart:async)

chunhunghan chunhunghan · Accepted Answer · 2019-09-10T07:27:00

your CLASSIFICATION might not correctly initialized.

please check example below

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

List<Map> _jsonApi1 = [
  {"id": 0, "name": "default 1"}
];
List<Map> _jsonApi2 = [
  {"id": 1, "name": "second 2"},
  {"id": 2, "name": "third 3"}
];
List<Map> _myJson = new List.from(_jsonApi1)..addAll(_jsonApi2);

class _MyHomePageState extends State<MyHomePage> {
  String _mySelection;

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: SafeArea(
        child: Column(
          children: <Widget>[
            Container(
              height: 500.0,
              child: new Center(
                child: new DropdownButton<String>(
                  isDense: true,
                  hint: new Text("${_jsonApi1[0]["name"]}"),
                  value: _mySelection,
                  onChanged: (String newValue) {
                    setState(() {
                      _mySelection = newValue;
                    });

                    print(_mySelection);
                  },
                  items: _myJson.map((Map map) {
                    return new DropdownMenuItem<String>(
                      value: map["id"].toString(),
                        child: new Text(
                          map["name"],
                        ),
                    );
                  }).toList(),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

getter 'classification' was called on null

1 Answers