Flutter file reading and writing --- detailed explanation of path_provider

Preface

In our actual application development process, we often do some local persistent data configuration, which can be obtained when the application starts to process the corresponding business logic. Or we need to download files, download pictures, etc. through the IO stream.

When we manipulate files we need to combine dart:io library path_provider , because of the different file paths under each system, if they are to achieve a lot of trouble, so path_provider this production.

Source code and video tutorial address

github source code address video tutorial address

Introduction to path_provider

path_provider is a Flutter plug-in. Its main function is to provide a platform-independent and consistent way to access the file system of the device, such as application temporary directories and document directories. And path_provider supports Android , iOS , Linux , MacOS , Windows .

path_provider App directory

There are eight types of app storage directories. Let’s take a look at their differences:

Temporary directory

The temporary directory is a cache folder that the system can empty at any time

The corresponding implementation for iOS is NSCachesDirectory
The corresponding implementation for Android is getCacheDir() )

Document directory

The document directory is used to store files that can only be accessed by the application. The system will not clear the directory and will only disappear when the application is deleted.

The corresponding implementation for iOS is NSDocumentDirectory
The corresponding implementation for Android is AppData

Application support catalog

The application support directory is used for files that you do not want to disclose to users, that is, files that you do not want to see to users can be placed in this directory. The system will not clear the directory, and will only disappear when the application is deleted.

The corresponding implementation for iOS is NSApplicationSupportDirectory
The corresponding implementation for Android is getFilesDir() )

Application persistent file directory

This directory is mainly a directory for storing persistent files and will not be disclosed to users. It is often used to store database files, such as sqlite.db.

External storage directory

It is mainly used to obtain external storage directories, such as SD cards, but iOS does not support external storage directories. Currently, only Android supports it.

External storage cache directory

The main user obtains the directory of application-specific external cache data, such as those with multiple storage directories on the SD card or mobile phone, but iOS does not support external storage directories, and currently only Android supports it.

External storage directory (separate partition)

The external storage directory can be obtained according to the type, such as SD card, separate partition, etc. The difference from the external storage directory is that it obtains an array of directories. However, iOS does not support external storage directories, and currently only Android supports it.

Desktop program download directory

The directory mainly used to store downloaded files, only applicable to Linux , MacOS , Windows , Android and iOS platforms cannot be used.

path_provider method and description

method	Attributes	describe
getTemporaryDirectory()	Future<Directory>	Temporary directory
getApplicationSupportDirectory()	Future<Directory>	Application support catalog
getLibraryDirectory()	Future<Directory>	Application persistent file directory
getApplicationDocumentsDirectory()	Future<Directory>	Document directory
getExternalStorageDirectory()	Future<Directory>	External storage directory
getExternalCacheDirectories()	Future<List<Directory>?>	External storage cache directory
getExternalStorageDirectories()	Future<List<Directory>?>	External storage directory (separate partition)
getDownloadsDirectory()	Future<Directory?>	Desktop program download directory

Basic use of path_provider

Here we give a simple example, path_provider and write the text to the file. The specific steps are as follows:

Add dependency
Get local directory
Write data to disk
Read disk data

The first step: add dependencies

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  path_provider: ^2.0.5

Step 2: Get the local directory

Although there are a total of eight kinds of access paths, in the actual application development process, we often use three types. Let's get the paths of these three directories respectively, as follows:

/// 获取文档目录文件
Future<File> _getLocalDocumentFile() async {
  final dir = await getApplicationDocumentsDirectory();
  return File('${dir.path}/str.txt');
}

/// 获取临时目录文件
Future<File> _getLocalTemporaryFile() async {
  final dir = await getTemporaryDirectory();
  return File('${dir.path}/str.txt');
}

/// 获取应用程序目录文件
Future<File> _getLocalSupportFile() async {
  final dir = await getApplicationSupportDirectory();
  return File('${dir.path}/str.txt');
}

Step 3: Write data to disk

Here we use writeAsString() to name to the disk. If you need to write synchronously, you can call writeAsStringSync() , or if you want to write by byte stream, you can call writeAsBytes() .

String name = "Jimi";

/// 写入数据
Future<void> writeString(String str) async {
  final file = await _getLocalDocumentFile();
  await file.writeAsString(name);

  final file1 = await _getLocalTemporaryFile();
  await file1.writeAsString(name);

  final file2 = await _getLocalSupportFile();
  await file2.writeAsString(name);
  print("写入成功");
}

Step 4: Read the disk data

try catch is added here to prevent an abnormality in reading the file and cause a crash. We read the files in the three directories and add corresponding printing to them.

/// 读取值
Future<void> readString() async {
  try {

    final file = await _getLocalDocumentFile();
    final result  = await file.readAsString();
    print("result-----$result");

    final file1 = await _getLocalTemporaryFile();
    final result1  = await file1.readAsString();
    print("result1-----$result1");

    final file2 = await _getLocalSupportFile();
    final result2  = await file2.readAsString();
    print("result2-----$result2");

  } catch (e) {
  }
}

Complete sample code

import 'dart:io';

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

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

class MyApp extends StatelessWidget {

  String name = "Jimi";

  /// 获取文档目录文件
  Future<File> _getLocalDocumentFile() async {
    final dir = await getApplicationDocumentsDirectory();
    return File('${dir.path}/str.txt');
  }

  /// 获取临时目录文件
  Future<File> _getLocalTemporaryFile() async {
    final dir = await getTemporaryDirectory();
    return File('${dir.path}/str.txt');
  }

  /// 获取应用程序目录文件
  Future<File> _getLocalSupportFile() async {
    final dir = await getApplicationSupportDirectory();
    return File('${dir.path}/str.txt');
  }

  /// 读取值
  Future<void> readString() async {
    try {

      final file = await _getLocalDocumentFile();
      final result  = await file.readAsString();
      print("result-----$result");

      final file1 = await _getLocalTemporaryFile();
      final result1  = await file1.readAsString();
      print("result1-----$result1");

      final file2 = await _getLocalSupportFile();
      final result2  = await file2.readAsString();
      print("result2-----$result2");


    } catch (e) {
    }
  }

  /// 写入数据
  Future<void> writeString(String str) async {
    final file = await _getLocalDocumentFile();
    await file.writeAsString(name);

    final file1 = await _getLocalTemporaryFile();
    await file1.writeAsString(name);

    final file2 = await _getLocalSupportFile();
    await file2.writeAsString(name);
    print("写入成功");
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(title: Text("path_provider"),),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text(name,
                style: TextStyle(
                    color: Colors.pink,
                    fontSize: 30
                ),
              ),
              SizedBox(height: 20),
              ElevatedButton(
                onPressed: (){
                  writeString(name);
                },
                child: Text("存入本地目录"),
              ),
              ElevatedButton(
                onPressed: (){
                  readString();
                },
                child: Text("读取值"),
              ),
            ],
          ),
        ),
      )
    );
  }
}

Console output

flutter: 写入成功
flutter: result-----Jimi
flutter: result1-----Jimi
flutter: result2-----Jimi

Summarize

When we need to persist data or download files, pictures or save database files, we write the files to disk, then we need to use dart:io and path_provider , and the path_provider is to provide a platform-independent and consistent way to access the files of the device System, such as application temporary directory, document directory, etc.