flutter 读写文件

配置：path_provider: ^1.6.5

import 'dart:io';
import 'dart:async';

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Ajnauw',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

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

class _MyHomePageState extends State {
  String value; // 每次input的值
  String allText = ''; // 从本地文件获取的值

  /**
   * 此方法返回本地文件地址
   */
  Future _getLocalFile() async {
    // 获取文档目录的路径
    Directory appDocDir = await getApplicationDocumentsDirectory();
    String dir = appDocDir.path;
    final file = new File('$dir/demo.txt');
    // print(file);
    return file;
  }

  /**
   * 保存value到本地文件里面
   */
  void _saveValue() async {
    try {
      File f = await _getLocalFile();
      IOSink slink = f.openWrite(mode: FileMode.append);
      slink.write('$value\n');
      // await fs.writeAsString('$value');
      setState(() {
        value = '';
      });
      slink.close();
    } catch (e) {
      // 写入错误
      print(e);
    }
  }

  /**
   * 读取本地文件的内容
   */
  void _readContent() async {
    File file = await _getLocalFile();
    // 从文件中读取变量作为字符串，一次全部读完存在内存里面
    String contents = await file.readAsString();
    setState(() {
      allText = contents;
    });
  }

  // 清空本地保存的文件
  void _clearContent() async {
    File f = await _getLocalFile();
    await f.writeAsString('');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('demo'),
      ),
      body: ListView(
        children: [
          Container(
            padding: EdgeInsets.all(8.0),
            child: Row(
              children: [
                Expanded(
                  child: Container(
                    margin: EdgeInsets.only(right: 16.0),
                    child: TextField(
                      controller: TextEditingController(
                        text: value,
                      ),
                      onChanged: (String v) {
                        value = v;
                      },
                      onSubmitted: (String r) {
                        value = r;
                      },
                    ),
                  ),
                ),
                RaisedButton(
                  color: Theme.of(context).primaryColor,
                  onPressed: _saveValue,
                  child: Text('保存'),
                ),
              ],
            ),
          ),
          Container(
            child: Column(
              children: [
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: [
                    RaisedButton(
                      color: Theme.of(context).accentColor,
                      onPressed: _readContent,
                      child: Text('获取本地数据'),
                    ),
                    RaisedButton(
                      color: Colors.red,
                      textColor: Colors.white,
                      onPressed: _clearContent,
                      child: Text('清空本地数据'),
                    ),
                  ],
                ),
                Container(
                  padding: const EdgeInsets.all(16.0),
                  child: Text('''$allText'''),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}