详解Flutter如何读写文本文件

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flutter:
  assets:
    - assets/

// main.dart
import 'package:flutter/material.dart';
import 'package:flutter/services.dart' show rootBundle;
import 'dart:async';
​
void main() {
  runApp(MyApp());
}
​
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: '坚果',
      home: HomePage(),
    );
  }
}
​
class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}
​
class _HomePageState extends State<HomePage> {
  String _data;
​
  // This function is triggered when the user presses the floating button
  Future<void> _loadData() async {
    final _loadedData = await rootBundle.loadString('assets/data.txt');
    setState(() {
      _data = _loadedData;
    });
  }
​
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('坚果'),
      ),
      body: Center(
          child: Container(
              width: 300,
              child: Text(_data != null ? _data : 'Nothing to show',
                  style: TextStyle(fontSize: 24)))),
      floatingActionButton:
          FloatingActionButton(onPressed: _loadData, child: Icon(Icons.add)),
    );
  }
}

dependencies:
  path_provider: ^2.0.8

flutter pub get

import 'package:path_provider/path_provider.dart';
​
/* .... */
​
Future<String> get _getDirPath async {
  final _dir = await getApplicationDocumentsDirectory();
  return _dir.path;
}

// main.dart
import 'dart:convert';
​
import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
​
void main() {
  runApp(MyApp());
}
​
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: '坚果',
      home: HomePage(),
    );
  }
}
​
class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}
​
class _HomePageState extends State<HomePage> {
  // This will be displayed on the screen
  String _content;
​
  // Find the Documents path
  Future<String> _getDirPath() async {
    final _dir = await getApplicationDocumentsDirectory();
    return _dir.path;
  }
​
  // This function is triggered when the "Read" button is pressed
  Future<void> _readData() async {
    final _dirPath = await _getDirPath();
    final _myFile = File('$_dirPath/data.txt');
    final _data = await _myFile.readAsString(encoding: utf8);
    setState(() {
      _content = _data;
    });
  }
​
  // TextField controller
  final _textController = TextEditingController();
  // This function is triggered when the "Write" buttion is pressed
  Future<void> _writeData() async {
    final _dirPath = await _getDirPath();
    
    final _myFile = File('$_dirPath/data.txt');
    // If data.txt doesn't exist, it will be created automatically
​
    await _myFile.writeAsString(_textController.text);
    _textController.clear();
  }
​
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('坚果'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(20),
        child: Column(
          children: [
            TextField(
              controller: _textController,
              decoration: InputDecoration(labelText: 'Enter your name'),
            ),
            ElevatedButton(
              child: Text('Save to file'),
              onPressed: _writeData,
            ),
            SizedBox(
              height: 150,
            ),
            Text(
                _content != null
                    ? _content
                    : 'Press the button to load your name',
                style: TextStyle(fontSize: 24, color: Colors.pink)),
            ElevatedButton(
              child: Text('Read my name from the file'),
              onPressed: _readData,
            )
          ],
        ),
      ),
    );
  }
}