如何使用颤振将 Base64 字符串解码为图像文件
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【中文标题】如何使用颤振将 Base64 字符串解码为图像文件【英文标题】:How to decode Base64 String to Image file with flutter 【发布时间】:2020-09-21 05:11:27 【问题描述】:我实际上是在尝试将图像文件转换为 Base64 并将 Base64 字符串解码为 Dart/Flutter 中的图像文件。事实上,我的应用程序使用相机插件拍照,然后将其作为 Base64 字符串保存在数据库中(因为我不知道其他方式,但可能有更相关的方式来存储多张图像?)。
我用这个代码编码:
final path = join(
(await getTemporaryDirectory()).path,
'$DateTime.now().png',
);
await _controller.takePicture(path);
final bytes = File(path).readAsBytesSync();
String img64 = base64Encode(bytes);
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => DisplayPictureScreen(imageAnalysed: img64),
),
);
并用这个解码:
class DisplayPictureScreen extends StatelessWidget
final String imageAnalysed;
const DisplayPictureScreen(Key key, this.imageAnalysed) : super(key: key);
@override
Widget build(BuildContext context)
final decodedBytes = base64Decode(imageAnalysed);
var fileImg= File("testImage.png");
fileImg..writeAsBytesSync(decodedBytes);
return Scaffold(
appBar: AppBar(title: Text('Display the Picture')),
body: Image.file(fileImg),
);
但是有这个错误:
The following FileSystemException was thrown building DisplayPictureScreen(dirty):
Cannot open file, path = 'testImage.png' (OS Error: Read-only file system, errno = 30)
如何解决我的问题并从 Base64 字符串中获取图像?
感谢您的帮助!
【问题讨论】:
***.com/a/46146008/11550065这个问题已经有人回答了 感谢您的快速回复,但使用 Image.memory 似乎无法解决我的问题,因为我需要一个文件在必要时裁剪图像(使用此包 pub.dev/packages/image_cropper)和 Image .memory 仅提供图像类型而不是文件。这就是为什么我尝试使用writeAsBytesSync
。
这个错误说明了你的问题(“OS Error: Read-only file system, errno = 30”),与base64解码无关。您似乎没有提供写入文件的绝对路径。当前目录是什么?您是否尝试写入根目录?
其实我是新手,所以我真的不知道我写的文件在哪里。我以为var fileImg= File("testImage.png")
创建了一个带有特定目录的临时文件。所以要解决这个问题我应该使用path_provider
来实现getTemporaryDirectory()
并在这个目录下创建一个临时文件?还是有更简单的?
【参考方案1】:
您可以在下面复制粘贴运行完整代码
您可以使用path_provider
获取getApplicationDocumentsDirectory
并使用bool
isLoading
控制写入文件完成时显示图像
代码sn-p
void writeFile() async
final decodedBytes = base64Decode(widget.imageAnalysed);
final directory = await getApplicationDocumentsDirectory();
fileImg = File('$directory.path/testImage.png');
print(fileImg.path);
fileImg.writeAsBytesSync(List.from(decodedBytes));
setState(()
isLoading = false;
);
@override
void initState()
WidgetsBinding.instance.addPostFrameCallback((_)
writeFile();
);
...
@override
Widget build(BuildContext context)
return isLoading ? CircularProgressIndicator() : Image.file(fileImg);
工作演示
完整代码
import 'dart:convert';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
import 'package:flutter/material.dart';
class DisplayPictureScreen extends StatefulWidget
final String imageAnalysed;
const DisplayPictureScreen(Key key, this.imageAnalysed) : super(key: key);
@override
_DisplayPictureScreenState createState() => _DisplayPictureScreenState();
class _DisplayPictureScreenState extends State<DisplayPictureScreen>
File fileImg;
bool isLoading = true;
void writeFile() async
final decodedBytes = base64Decode(widget.imageAnalysed);
final directory = await getApplicationDocumentsDirectory();
fileImg = File('$directory.path/testImage.png');
print(fileImg.path);
fileImg.writeAsBytesSync(List.from(decodedBytes));
setState(()
isLoading = false;
);
@override
void initState()
WidgetsBinding.instance.addPostFrameCallback((_)
writeFile();
);
super.initState();
@override
Widget build(BuildContext context)
return isLoading ? CircularProgressIndicator() : Image.file(fileImg);
void main()
runApp(MyApp());
class MyApp extends StatelessWidget
@override
Widget build(BuildContext context)
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
class MyHomePage extends StatefulWidget
MyHomePage(Key key, this.title) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
class _MyHomePageState extends State<MyHomePage>
int _counter = 0;
String base64String =
'''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''';
void _incrementCounter()
setState(()
_counter++;
);
@override
Widget build(BuildContext context)
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
DisplayPictureScreen(imageAnalysed: base64String),
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
【讨论】:
太棒了,效果很好!代码非常好理解和完整,我不知道WidgetsBinding.instance.addPostFrameCallback
,但我相信我会再次使用它。非常感谢!
很高兴为您提供帮助。如果对您有帮助,请将其标记为答案。谢谢。以上是关于如何使用颤振将 Base64 字符串解码为图像文件的主要内容,如果未能解决你的问题,请参考以下文章