第十六章：Flutter数据存储

Flutter的数据存储分为三类

• Preferences
• 文件存储
• 数据库

Preferences

Preference相当于iOS的NSUserDefaults,其实也是按plist的方式存储的

step1:添加依赖

# 添加sharedPreference依赖
 shared_preferences: ^0.5.0

step2:pub get

step3:导入头文件

import 'package:shared_preferences/shared_preferences.dart';

使用方法：

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

// 创建一个新路由
class shared_preferences_Route extends StatefulWidget {
  @override // 重写
  State<StatefulWidget> createState() => StorageState();
}

class StorageState extends State {
  var _textFieldController = new TextEditingController();
  var _storageString = '';
  final STORAGE_KEY = 'storage_key';

  /**
   * 利用SharedPreferences存储数据
   */
  Future saveString() async {
    SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
    sharedPreferences.setString(
        STORAGE_KEY, _textFieldController.value.text.toString());
  }

  /**
   * 获取存在SharedPreferences中的数据
   */
  Future getString() async {
    SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
    setState(() {
      _storageString = sharedPreferences.get(STORAGE_KEY);
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Shared Preferences存储'),
      ),
      body: new Column(
        children: <Widget>[
          Text("请输入文本", textAlign: TextAlign.center),
          TextField(
            controller: _textFieldController,
          ),
          MaterialButton(
            onPressed: saveString,
            child: new Text("存储"),
            color: Colors.pink,
          ),
          MaterialButton(
            onPressed: getString,
            child: new Text("获取"),
            color: Colors.lightGreen,
          ),
          Text('shared_preferences存储的值为  $_storageString'),


        ],
      ),
    );
  }
}

文件存储

在path_provider中有三个获取文件路径的方法：
- getTemporaryDirectory()
://获取应用缓存目录，等同iOS的NSTemporaryDirectory()和Android的getCacheDir() 方法。
- getApplicationDocumentsDirectory():
//获取应用文件目录类似于iOS的NSDocumentDirectory和Android上的 AppData目录。

step1:添加依赖

# 添加文件依赖
path_provider: ^0.5.0

step2:pub get

step3:导入头文件

import 'package:path_provider/path_provider.dart';
import 'dart:io';

使用方法：

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

// 创建一个新路由
class file_Route extends StatefulWidget {
  @override // 重写
  State<StatefulWidget> createState() => StorageState();
}

class StorageState extends State {
  var _textFieldController = new TextEditingController();
  var _storageString = '';

  /**
   * 利用文件存储数据
   */
  saveString() async {
    final file = await getFile('file.text');
    //写入字符串
    file.writeAsString(_textFieldController.value.text.toString());
  }

  /**
   * 获取存在文件中的数据
   */
  Future getString() async {
    final file = await getFile('file.text');
    var filePath  = file.path;
    setState(() {
      file.readAsString().then((String value) {
        _storageString = value +'\n文件存储路径：'+filePath;
      });
    });
  }

  /**
   * 初始化文件路径
   */
  Future<File> getFile(String fileName) async {
    //获取应用文件目录类似于Ios的NSDocumentDirectory和Android上的 AppData目录
    final fileDirectory = await getApplicationDocumentsDirectory();

    //获取存储路径
    final filePath = fileDirectory.path;

    //或者file对象（操作文件记得导入import 'dart:io'）
    return new File(filePath + "/"+fileName);
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('文件存储'),
      ),
      body: new Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Text("文件存储", textAlign: TextAlign.center),
          TextField(
            controller: _textFieldController,
          ),
          MaterialButton(
            onPressed: saveString,
            child: new Text("存储"),
            color: Colors.cyan,
          ),
          MaterialButton(
            onPressed: getString,
            child: new Text("获取"),
            color: Colors.deepOrange,
          ),
          Text('从文件存储中获取的值为  $_storageString'),
        ],
      ),
    );
  }
}