Flutter/Dart 变量丢失/尝试从不同 class 获取时不断重新初始化

Question

当从另一个 class 访问时，变量不断重新初始化。

我有一个 class，在其单独的飞镖源文件中，声明如下：

helper_provider.dart

import 'package:flutter/material.dart';

class BuilderHelperProvider extends ChangeNotifier {
  var _builderDetails;

  void setBuilderDetails(inputDetails) {
    this._builderDetails = inputDetails;
  }

  get builderDetails {
    return _builderDetails;
  }
}

然后我在main.dart

中初始化变量

main.dart

import 'package:builder_project/helpers/helper_provider.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(
          create: (context) => BuilderHelperProvider(),
        ),
      ],
      child: MaterialApp(
          debugShowCheckedModeBanner: false,
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
            visualDensity: VisualDensity.adaptivePlatformDensity,
          ),
          home: StreamBuilder(
              stream: FirebaseFirestore.instance
                  .collection('builders')
                  .doc('builder id')
                  .snapshots(),
              builder: (context, builderSnap) {
                if (builderSnap.connectionState == ConnectionState.waiting) {
                  return Center(child: CircularProgressIndicator());
                }
                final _builderDetails = builderSnap.data;

                BuilderHelperProvider().setBuilderDetails(_builderDetails);

                print('builder Details: ${BuilderHelperProvider().builderDetails}');
                # *This keeps returning null*

                return BuilderHomepage();
              })
          // home: BuilderHomepage(),
          ),
    );
  }
}

以上代码的输出结果为：

I/flutter (31260): builder Details: null

我的应用程序在两次操作之间没有退出或停止。什么情况下会重新激活？

Answer 1

只需将它们设为静态就可以了

static  var _builderDetails;

Flutter/Dart 变量丢失/尝试从不同 class 获取时不断重新初始化

Flutter/Dart variables lost / keep getting reinitialized when trying to get from different class

dart

dart-pub

flutter

flutter-dependencies