从设备存储读取图像文件并转换为 Base64 会导致 Flutter 中的 Base64 无效

Question

我正在尝试从已知路径读取文件并从图像中获取 base64 字符串。我还是不明白为什么 Base64 被破坏了。这种情况仅发生在 Flutter 代码中。

我尝试使用简单的 Dart 程序进行相同的转换，我得到了所需的 Base64 字符串。 Flutter 中出现此问题。

onPressed: () async {
  File imageFile =
      await ImagePicker.pickImage(source: ImageSource.camera);
  if (imageFile != null) {
    Uint8List bytes = await imageFile.readAsBytes();
    String base64data = base64.encode(bytes);
    print(base64data);
  }
}

以下是我的控制台输出：

W/ExifInterface(15331): Skip the tag entry since tag number is not defined: 2
W/ExifInterface(15331): Stop reading file since a wrong offset may cause an infinite loop: 0
I/chatty  (15331): uid=10271(com.crowdanalytix.datax_app) Binder:15331_5 identical 2 lines
W/ExifInterface(15331): Stop reading file since a wrong offset may cause an infinite loop: 0
I/flutter (15331): 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

我得到的 Base64 字符串无效。有人可以试试这个吗？

我使用的是 OnePlus3t (ONEPLUS A3003)。

Answer 1

打印功能没有打印所有内容。
您可以使用调试模式看到完整结果

代码片段

    List<int> imageBytes = await _imageFile.readAsBytes();
    String base64Image = base64Encode(imageBytes);
    print(base64Image);

从调试模式复制base64字符串并粘贴到在线转换器，您可以看到结果是正确的。

来自官方演示的完整代码并添加base64转换

// Copyright 2019 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:io';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:video_player/video_player.dart';
import 'dart:typed_data';
import 'package:image/image.dart' as ImageProcess;

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Image Picker Demo',
      home: MyHomePage(title: 'Image Picker Example'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  File _imageFile;
  dynamic _pickImageError;
  bool isVideo = false;
  VideoPlayerController _controller;
  String _retrieveDataError;

  Future<void> _playVideo(File file) async {
    if (file != null && mounted) {
      await _disposeVideoController();
      _controller = VideoPlayerController.file(file);
      await _controller.setVolume(1.0);
      await _controller.initialize();
      await _controller.setLooping(true);
      await _controller.play();
      setState(() {});
    }
  }

  void _onImageButtonPressed(ImageSource source) async {
    if (_controller != null) {
      await _controller.setVolume(0.0);
    }
    if (isVideo) {
      final File file = await ImagePicker.pickVideo(source: source);
      await _playVideo(file);
    } else {
      try {
        _imageFile = await ImagePicker.pickImage(source: source);

        List<int> imageBytes = await _imageFile.readAsBytes();
        String base64Image = base64Encode(imageBytes);
        print(base64Image);

        setState(() {});
      } catch (e) {
        _pickImageError = e;
      }
    }
  }

  @override
  void deactivate() {
    if (_controller != null) {
      _controller.setVolume(0.0);
      _controller.pause();
    }
    super.deactivate();
  }

  @override
  void dispose() {
    _disposeVideoController();
    super.dispose();
  }

  Future<void> _disposeVideoController() async {
    if (_controller != null) {
      await _controller.dispose();
      _controller = null;
    }
  }

  Widget _previewVideo() {
    final Text retrieveError = _getRetrieveErrorWidget();
    if (retrieveError != null) {
      return retrieveError;
    }
    if (_controller == null) {
      return const Text(
        'You have not yet picked a video',
        textAlign: TextAlign.center,
      );
    }
    return Padding(
      padding: const EdgeInsets.all(10.0),
      child: AspectRatioVideo(_controller),
    );
  }

  Widget _previewImage() {
    final Text retrieveError = _getRetrieveErrorWidget();
    if (retrieveError != null) {
      return retrieveError;
    }
    if (_imageFile != null) {
      return Image.file(_imageFile);
    } else if (_pickImageError != null) {
      return Text(
        'Pick image error: $_pickImageError',
        textAlign: TextAlign.center,
      );
    } else {
      return const Text(
        'You have not yet picked an image.',
        textAlign: TextAlign.center,
      );
    }
  }

  Future<void> retrieveLostData() async {
    final LostDataResponse response = await ImagePicker.retrieveLostData();
    if (response.isEmpty) {
      return;
    }
    if (response.file != null) {
      if (response.type == RetrieveType.video) {
        isVideo = true;
        await _playVideo(response.file);
      } else {
        isVideo = false;
        setState(() {
          _imageFile = response.file;
        });
      }
    } else {
      _retrieveDataError = response.exception.code;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Platform.isAndroid
            ? FutureBuilder<void>(
          future: retrieveLostData(),
          builder: (BuildContext context, AsyncSnapshot<void> snapshot) {
            switch (snapshot.connectionState) {
              case ConnectionState.none:
              case ConnectionState.waiting:
                return const Text(
                  'You have not yet picked an image.',
                  textAlign: TextAlign.center,
                );
              case ConnectionState.done:
                return isVideo ? _previewVideo() : _previewImage();
              default:
                if (snapshot.hasError) {
                  return Text(
                    'Pick image/video error: ${snapshot.error}}',
                    textAlign: TextAlign.center,
                  );
                } else {
                  return const Text(
                    'You have not yet picked an image.',
                    textAlign: TextAlign.center,
                  );
                }
            }
          },
        )
            : (isVideo ? _previewVideo() : _previewImage()),
      ),
      floatingActionButton: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          FloatingActionButton(
            onPressed: () {
              isVideo = false;
              _onImageButtonPressed(ImageSource.gallery);
            },
            heroTag: 'image0',
            tooltip: 'Pick Image from gallery',
            child: const Icon(Icons.photo_library),
          ),
          Padding(
            padding: const EdgeInsets.only(top: 16.0),
            child: FloatingActionButton(
              onPressed: () {
                isVideo = false;
                _onImageButtonPressed(ImageSource.camera);
              },
              heroTag: 'image1',
              tooltip: 'Take a Photo',
              child: const Icon(Icons.camera_alt),
            ),
          ),
          Padding(
            padding: const EdgeInsets.only(top: 16.0),
            child: FloatingActionButton(
              backgroundColor: Colors.red,
              onPressed: () {
                isVideo = true;
                _onImageButtonPressed(ImageSource.gallery);
              },
              heroTag: 'video0',
              tooltip: 'Pick Video from gallery',
              child: const Icon(Icons.video_library),
            ),
          ),
          Padding(
            padding: const EdgeInsets.only(top: 16.0),
            child: FloatingActionButton(
              backgroundColor: Colors.red,
              onPressed: () {
                isVideo = true;
                _onImageButtonPressed(ImageSource.camera);
              },
              heroTag: 'video1',
              tooltip: 'Take a Video',
              child: const Icon(Icons.videocam),
            ),
          ),
        ],
      ),
    );
  }

  Text _getRetrieveErrorWidget() {
    if (_retrieveDataError != null) {
      final Text result = Text(_retrieveDataError);
      _retrieveDataError = null;
      return result;
    }
    return null;
  }
}

class AspectRatioVideo extends StatefulWidget {
  AspectRatioVideo(this.controller);

  final VideoPlayerController controller;

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

class AspectRatioVideoState extends State<AspectRatioVideo> {
  VideoPlayerController get controller => widget.controller;
  bool initialized = false;

  void _onVideoControllerUpdate() {
    if (!mounted) {
      return;
    }
    if (initialized != controller.value.initialized) {
      initialized = controller.value.initialized;
      setState(() {});
    }
  }

  @override
  void initState() {
    super.initState();
    controller.addListener(_onVideoControllerUpdate);
  }

  @override
  void dispose() {
    controller.removeListener(_onVideoControllerUpdate);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    if (initialized) {
      return Center(
        child: AspectRatio(
          aspectRatio: controller.value?.aspectRatio,
          child: VideoPlayer(controller),
        ),
      );
    } else {
      return Container();
    }
  }
}