firebase-realtime-database - フラッター グリッドビューにfirebaseデータをボタンのように表示させる方法

Question

ユーザー Streambuilder を使用してグリッドビューを表示しようとしていますが、このエラーが返されます。メソッド classList() をスキャフォールド本体のコンテナーに呼び出しています

データベース = FirebaseDatabase.instance

classData を表示したい、0,1,2..etc を表示したい ('className','classSection' を子ごとに 1 つのボタンで) グリッドビューで RaisedButtons として表示したい

以下のコードを実行すると、このエラーが発生します

I/flutter ( 5433): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 5433): The following NoSuchMethodError was thrown building HomePage(dirty, state: _HomePage#055be):
I/flutter ( 5433): The method 'split' was called on null.
I/flutter ( 5433): Receiver: null
I/flutter ( 5433): Tried calling: split("/")
I/flutter ( 5433): 
I/flutter ( 5433): When the exception was thrown, this was the stack:
I/flutter ( 5433): #0      Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
I/flutter ( 5433): #1      DatabaseReference.child (file:///G:/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_database-2.0.3/lib/src/database_reference.dart:24:58)
I/flutter ( 5433): #2      _HomePage.classList (package:barcode_scan_example/home_page.dart:169:44)
I/flutter ( 5433): #3      _HomePage.build (package:barcode_scan_example/home_page.dart:265:30)
I/flutter ( 5433): #4      StatefulElement.build (package:flutter/src/widgets/framework.dart:3825:27)
I/flutter ( 5433): #5      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3736:15)
I/flutter ( 5433): #6      Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter ( 5433): #7      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3716:5)
I/flutter ( 5433): #8      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3864:11)
I/flutter ( 5433): #9      ComponentElement.mount (package:flutter/src/widgets/framework.dart:3711:5)
I/flutter ( 5433): #10     Element.inflateWidget (package:flutter/src/widgets/framework.dart:2956:14)
I/flutter ( 5433): #11     Element.updateChild (package:flutter/src/widgets/framework.dart:2759:12)
I/flutter ( 5433): #12     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3747:16)
I/flutter ( 5433): #13     Element.rebuild (package:flutter/src/widgets/framework.dart:3559:5)
I/flutter ( 5433): #14     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2273:33)
I/flutter ( 5433): #15     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:700:20)
I/flutter ( 5433): #16     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:268:5)
I/flutter ( 5433): #17     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:988:15)
I/flutter ( 5433): #18     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:928:9)
I/flutter ( 5433): #19     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:840:5)
I/flutter ( 5433): #23     _invoke (dart:ui/hooks.dart:209:10)
I/flutter ( 5433): #24     _drawFrame (dart:ui/hooks.dart:168:3)
I/flutter ( 5433): (elided 3 frames from package dart:async)

classList() {
    StreamBuilder(
        stream:
            database.reference().child('user').child(userUid).child('classData').orderByKey().onValue,
        builder: (BuildContext context, AsyncSnapshot<Event> snapshot) {
          if (snapshot.hasData) {
            if (snapshot.data.snapshot.value != null) {
              Map<dynamic, dynamic> map = snapshot.data.snapshot.value;
              List<dynamic> list = map.values.toList();
              print("list is : $list");

              return GridView.builder(
                gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                    crossAxisCount: 3),
                itemCount: list.length,
                padding: EdgeInsets.all(2.0),
                itemBuilder: (BuildContext context, int index) {
                  print("print job ${list[index]["className"]}");
                  return Container(
                    child: RaisedButton(
                      onPressed: null,
                      child: Text(
                          "${list[index]["className"]}\n ${list[index]["classSection"]}"),
                    ),
                    padding: EdgeInsets.all(2.0),
                  );
                },
              );
            } else {
              return Container(
                  child: Center(
                      child: Text(
                "There's no Class registered in the system",
                style: TextStyle(fontSize: 20.0, color: Colors.grey),
                textAlign: TextAlign.center,
              )));
            }
          } else {
            return CircularProgressIndicator();
          }
        });
  }

ダーツファイル全体

import 'package:flutter/material.dart';
import 'auth.dart';
import 'auth_provider.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/services.dart';
import 'make_class.dart';
import 'dart:async';
import 'package:barcode_scan/barcode_scan.dart';
import 'package:firebase_database/firebase_database.dart';
import 'qr_screen.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePage createState() => _HomePage();
}

enum ScaffoldType { student, lecturer }

ScaffoldType _scaffoldType = ScaffoldType.lecturer;

class _HomePage extends State<HomePage> {
  final FirebaseDatabase database = FirebaseDatabase.instance;

  String barcode = "";
  String userUid;
  var userClass;



  Future<void> _signOut(BuildContext context) async {
    try {
      final BaseAuth auth = AuthProvider.of(context).auth;
      await auth.signOut();
    } catch (e) {
      print(e);
    }
  }

  @override
  void initState() {
    super.initState();
    userUi();
    setState(() async* {
      FirebaseDatabase database;
      database = FirebaseDatabase.instance;
      database.setPersistenceEnabled(true);
      database.setPersistenceCacheSizeBytes(10000000);
    });
  }

  Future reUser() async {
    FirebaseUser user = await FirebaseAuth.instance.currentUser();
    print(user.uid);
    var userUid = user.uid;
    var userWho = await database
        .reference()
        .child('user')
        .child(userUid)
        .once()
        .then((DataSnapshot snapshot) {
      Map<dynamic, dynamic> data = snapshot.value;
      var isL = data.values.toList();
      print(isL[1]);
      print(data.values);
      if (isL[1].toString().toLowerCase() == "true") {
        _scaffoldType = ScaffoldType.lecturer;
        print('lecturer');
      } else if (isL[1].toString().toLowerCase() == "false") {
        _scaffoldType = ScaffoldType.student;
        print("student");
      }
    });
//        print(userWho);
  }



  userUi() async {
    FirebaseUser user = await FirebaseAuth.instance.currentUser();
    print(user.uid);
    return user.uid;
  }

  classList(userUid) {

    print(userUid);
    StreamBuilder(
        stream:
        database.reference().child('user').child(userUid).child('classData').orderByKey().onValue,
        builder: (BuildContext context, AsyncSnapshot<Event> snapshot) {
          if (snapshot.hasData) {
            if (snapshot.data.snapshot.value != null) {
              Map<dynamic, dynamic> map = snapshot.data.snapshot.value;
              List<dynamic> list = map.values.toList();
              print("list is : $list");

              return GridView.builder(
                gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                    crossAxisCount: 3),
                itemCount: list.length,
                padding: EdgeInsets.all(2.0),
                itemBuilder: (BuildContext context, int index) {
                  print("print job ${list[index]["className"]}");
                  return Container(
                    child: RaisedButton(
                      onPressed: (){},
                      child: Text(
                          "${list[index]["className"]}\n ${list[index]["classSection"]}"),
                    ),
                    padding: EdgeInsets.all(2.0),
                  );
                },
              );
            } else {
              return Container(
                  child: Center(
                      child: Text(
                        "There's no Class registered in the system",
                        style: TextStyle(fontSize: 20.0, color: Colors.grey),
                        textAlign: TextAlign.center,
                      )));
            }
          } else {
            return CircularProgressIndicator();
          }
        });
  }

  @override
  Widget build(BuildContext context) {
//    var userUid = userUi();
    reUser();
    return Scaffold(
      appBar: AppBar(
        title: Text('Welcome'),
        actions: <Widget>[
          FlatButton(
            child: Icon(Icons.exit_to_app),
            onPressed: () => _signOut(context),
          )
        ],
      ),
      bottomNavigationBar: BottomAppBar(
        notchMargin: 8.0,
        child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Padding(
            padding: const EdgeInsets.fromLTRB(35, 0, 35, 0),
            child: Row(
              mainAxisSize: MainAxisSize.max,
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                Column(
                  mainAxisSize: MainAxisSize.min,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: buttonBelow(),
                ),
                Column(
                  mainAxisSize: MainAxisSize.min,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: buttonBelow2(),
                ),
              ],
            ),
          ),
        ),
        shape: CircularNotchedRectangle(),
      ),
      resizeToAvoidBottomInset: true,
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      floatingActionButton: Container(
        height: 80,
        width: 80,
        child: FittedBox(
          child: FloatingActionButton(
            onPressed: scan,
            child: Icon(
              Icons.camera,
              size: 35,
            ),
            elevation: 2.0,
          ),
        ),
      ),
      body: Container(child: classList(userUi()),),
    );
  }

  List<Widget> buttonBelow() {
    if (_scaffoldType == ScaffoldType.lecturer) {
      return <Widget>[
        FlatButton(
          child: Icon(
            Icons.add_circle,
            semanticLabel: "Add Class",
            size: 45,
          ),
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => MakeClass()),
            );
          },
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(180)),
        ),
        Text("Add Class")
      ];
    } else {
      return <Widget>[
        Opacity(
          opacity: 0,
          child: FlatButton(
            onPressed: () {},
            child: Icon(
              Icons.add_circle,
              semanticLabel: "Add Class",
              size: 45,
            ),
            shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.circular(180)),
          ),
        ),
        Opacity(opacity: 0, child: Text("Add Class"))
      ];
    }
  }
  List<Widget> buttonBelow2() {
    if (_scaffoldType == ScaffoldType.lecturer) {
      return <Widget>[
        FlatButton(
          child: Icon(
            Icons.blur_on,
            semanticLabel: "QRCode",
            size: 45,
          ),
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(builder: (context) => QrScreen()),
            );
          },
          shape:
          RoundedRectangleBorder(borderRadius: BorderRadius.circular(180)),
        ),
        Text("QRCode")
      ];
    }
  }

  Future scan() async {
    try {
      String barcode = await BarcodeScanner.scan();
      setState(() => this.barcode = barcode);
    } on PlatformException catch (e) {
      if (e.code == BarcodeScanner.CameraAccessDenied) {
        setState(() {
          this.barcode = 'The user did not grant the camera permission!';
        });
      } else {
        setState(() => this.barcode = 'Unknown error: $e');
      }
    } on FormatException {
      setState(() => this.barcode =
          'null (User returned using the "back"-button before scanning anything. Result)');
    } catch (e) {
      setState(() => this.barcode = 'Unknown error: $e');
    }
  }
}