在Flutter开发中，集成主流功能通常依赖于一系列高质量、社区维护的插件。mainstream 这个词并不是一个具体的Flutter插件名称，但我们可以理解为你想要集成一系列在Flutter应用中常用的功能插件。以下是一些主流功能的插件及其使用示例代码：

1. 网络请求：http 插件

用于发送HTTP请求，获取数据。

pubspec.yaml

dependencies:
  http: ^0.13.3

使用示例

import 'package:http/http.dart' as http;
import 'dart:convert';

Future<void> fetchData() async {
  final response = await http.get(Uri.parse('https://api.example.com/data'));

  if (response.statusCode == 200) {
    Map<String, dynamic> data = jsonDecode(response.body);
    print(data);
  } else {
    throw Exception('Failed to load data');
  }
}

2. 状态管理：provider 插件

用于在Flutter应用中管理应用状态。

pubspec.yaml

dependencies:
  provider: ^6.0.0

使用示例

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

void main() {
  runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
      ],
      child: MyApp(),
    ),
  );
}

class Counter with ChangeNotifier {
  int _count = 0;
  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Counter')),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              Text(
                '${Provider.of<Counter>(context).count}',
                style: Theme.of(context).textTheme.headline4,
              ),
            ],
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            Provider.of<Counter>(context, listen: false).increment();
          },
          tooltip: 'Increment',
          child: Icon(Icons.add),
        ),
      ),
    );
  }
}

3. 图片选择：image_picker 插件

用于从设备图库或相机中选择图片。

pubspec.yaml

dependencies:
  image_picker: ^0.8.4+3

使用示例

import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Image Picker')),
        body: Center(
          child: MyHomePage(),
        ),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  File? _image;

  final ImagePicker _picker = ImagePicker();

  Future<void> _pickImage(ImageSource source) async {
    final pickedFile = await _picker.pickImage(source: source);

    setState(() {
      if (pickedFile != null) {
        _image = File(pickedFile!.path);
      } else {
        _image = null;
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        _image == null
            ? Text('No image selected.')
            : Image.file(_image!),
        SizedBox(height: 20),
        ElevatedButton(
          onPressed: () => _pickImage(ImageSource.gallery),
          child: Text('Pick image from gallery'),
        ),
        SizedBox(height: 20),
        ElevatedButton(
          onPressed: () => _pickImage(ImageSource.camera),
          child: Text('Pick image from camera'),
        ),
      ],
    );
  }
}

4. 本地存储：shared_preferences 插件

用于在设备上存储键值对数据。

pubspec.yaml

dependencies:
  shared_preferences: ^2.0.9

使用示例

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('SharedPreferences')),
        body: Center(
          child: MyHomePage(),
        ),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late SharedPreferences _preferences;

  @override
  void initState() {
    super.initState();
    _loadPreferences();
  }

  Future<void> _loadPreferences() async {
    _preferences = await SharedPreferences.getInstance();
    setState(() {});
  }

  Future<void> _saveData(String key, String value) async {
    await _preferences.setString(key, value);
  }

  Future<String?> _loadData(String key) async {
    return _preferences.getString(key);
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        ElevatedButton(
          onPressed: () async {
            await _saveData('myKey', 'myValue');
            final String? value = await _loadData('myKey');
            print(value);
          },
          child: Text('Save and Load Data'),
        ),
      ],
    );
  }
}

这些示例展示了如何在Flutter应用中集成和使用一些主流功能的插件。根据项目的具体需求，你可以进一步扩展和定制这些功能。