Flutter變數看起來像是有兩個資料

我想使用一個變數，我想用 firebase 資料填充它。在 Firebase 部分，它用正確的資料填充并正確列印以進行記錄，但之后在 Scaffold 中它看起來像使用起始宣告中的資料。但為什么？一個變數有兩個資料？因此，在 Text('$masik') 中的代碼末尾，我想使用 firebase 資料，而不是起始字串。我究竟做錯了什么？

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String masik = '';
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firebase',
      home: AddData(),
    );
  }
}

class AddData extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    String doksi = 'valami más';
    var ezlett;
    String masik = 'minden';
    String sajt = '';

    final Stream<QuerySnapshot> collectionStream = FirebaseFirestore.instance.collection('zenek').snapshots();

    FirebaseFirestore.instance
        .collection('zenek')
        .doc(doksi)
        .get()
        .then((DocumentSnapshot documentSnapshot) {
      if (documentSnapshot.exists) {
        String ezegyszoveg = documentSnapshot.data().toString();
        print('Document exists on the database $ezegyszoveg');
        ezlett = ezegyszoveg.substring(9, ezegyszoveg.indexOf(','));
        print(ezlett);
        masik = ezegyszoveg.substring(ezegyszoveg.indexOf('text: ') 6, ezegyszoveg.indexOf('}'));
        print(masik);

      }
    });

    return Scaffold(

      appBar: AppBar(
        backgroundColor: Colors.green,
        title: const Text("próba"),
      ),

      body:Row(
        children: [
          Text('$masik'),
        ],
      )

    );
  }
}

uj5u.com熱心網友回復：

嘿，你犯了一個愚蠢的錯誤，你必須在更新變數時使用 setState ：

   setState(){
          masik = ezegyszoveg.substring(ezegyszoveg.indexOf('text: ') 6,ezegyszoveg.indexOf('}'));
           } // this line put in setState in your code 

uj5u.com熱心網友回復：

當有新資料更新時，像這個例子這樣的東西將用于更新 UI

    import 'package:flutter/material.dart';
    import 'package:cloud_firestore/cloud_firestore.dart';
    import 'package:firebase_core/firebase_core.dart';

    void main() async {
      WidgetsFlutterBinding.ensureInitialized();
      await Firebase.initializeApp();
      runApp(MyApp());
    }

    class MyApp extends StatefulWidget {
      @override
      State<MyApp> createState() => _MyAppState();
    }

    class _MyAppState extends State<MyApp> {
      String masik = '';
      @override
      Widget build(BuildContext context) {
        return MaterialApp(
          title: 'Firebase',
          home: AddData(),
        );
      }
    }

    class AddData extends StatefulWidget {
      @override
      State<AddData> createState() => _AddDataState();
    }

    class _AddDataState extends State<AddData> {
      String doksi = 'valami más';
      var ezlett;
      String masik = 'minden';
      String sajt = '';
      @override
      void initState() {
        super.initState();
        updateTheUi();
      }

      void updateTheUi() {
        final Stream<QuerySnapshot> collectionStream =
            FirebaseFirestore.instance.collection('zenek').snapshots();

        FirebaseFirestore.instance
            .collection('zenek')
            .doc(doksi)
            .get()
            .then((DocumentSnapshot documentSnapshot) {
          if (documentSnapshot.exists) {
            String ezegyszoveg = documentSnapshot.data().toString();
            ezlett = ezegyszoveg.substring(9, ezegyszoveg.indexOf(','));
            masik = ezegyszoveg.substring(
                ezegyszoveg.indexOf('text: ')   6, ezegyszoveg.indexOf('}'));
            setState(() {});
          }
        });
      }

      @override
      Widget build(BuildContext context) {
        return Scaffold(
            appBar: AppBar(
              backgroundColor: Colors.green,
              title: const Text("próba"),
            ),
            body: Row(
              children: [
                Text('$masik'),
              ],
            ));
      }
    }

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