[移动开发]【Flutter】篇9：相机

挑选系统的相册，调用相机的功能，需要用到官网插件image_picker

官网代码

【运行报错】

ERROR:D8: Cannot fit requested classes in a single dex file (# methods: 68998 > 65536)
com.android.builder.dexing.DexArchiveMergerException: Error while merging dex archives: 
The number of method references in a .dex file cannot exceed 64K.

【解决】
启动MultiDex
【怎么启动】

1. 如果您的 minSdkVersion 为 21 或更高版本，系统会默认启用 MultiDex，并且您不需要 MultiDex 库
   在 根目录/app/src/main/AndroidManifest.xml更改即可
   

官网代码

// Copyright 2013 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.

// ignore_for_file: public_member_api_docs

import 'dart:async';
import 'dart:io';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:video_player/video_player.dart';

class MyImagePicker extends StatelessWidget {
  const MyImagePicker({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Image Picker Demo',
      home: MyHomePage(title: 'Image Picker Example'),
    );
  }
}

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

  final String? title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<XFile>? _imageFileList;

  void _setImageFileListFromFile(XFile? value) {
    _imageFileList = value == null ? null : <XFile>[value];
  }

  dynamic _pickImageError;
  bool isVideo = false;

  VideoPlayerController? _controller;
  VideoPlayerController? _toBeDisposed;
  String? _retrieveDataError;

  final ImagePicker _picker = ImagePicker();
  final TextEditingController maxWidthController = TextEditingController();
  final TextEditingController maxHeightController = TextEditingController();
  final TextEditingController qualityController = TextEditingController();
  //取得视频的资源之后进行视频的播放
  Future<void> _playVideo(XFile? file) async {
    if (file != null && mounted) {
      await _disposeVideoController();
      late VideoPlayerController controller;
      if (kIsWeb) {
        controller = VideoPlayerController.network(file.path);
      } else {
        controller = VideoPlayerController.file(File(file.path));
      }
      _controller = controller;
      // In web, most browsers won't honor a programmatic call to .play
      // if the video has a sound track (and is not muted).
      // Mute the video so it auto-plays in web!
      // This is not needed if the call to .play is the result of user
      // interaction (clicking on a "play" button, for example).
      //控制视频的播放
      const double volume = kIsWeb ? 0.0 : 1.0;
      await controller.setVolume(volume);
      await controller.initialize();
      await controller.setLooping(true);
      await controller.play();
      setState(() {});
    }
  }
  /**点击右侧浮游按钮的处理方法
   * */
  Future<void> _onImageButtonPressed(ImageSource source,
      {BuildContext? context, bool isMultiImage = false}) async {
    if (_controller != null) {
      await _controller!.setVolume(0.0);
    }
    //处理Video
    if (isVideo) {
      //调用插件方法
      final XFile? file = await _picker.pickVideo(
          source: source, maxDuration: const Duration(seconds: 10));
      await _playVideo(file);
    }
    //处理多张照片
    else if (isMultiImage) {
      await _displayPickImageDialog(context!,
              (double? maxWidth, double? maxHeight, int? quality) async {
            try {
              //调用插件方法
              final List<XFile>? pickedFileList = await _picker.pickMultiImage(
                maxWidth: maxWidth,
                maxHeight: maxHeight,
                imageQuality: quality,
              );
              setState(() {
                _imageFileList = pickedFileList;
              });
            } catch (e) {
              setState(() {
                _pickImageError = e;
              });
            }
          });
    }
    //处理一张照片
    else {
      await _displayPickImageDialog(context!,
              (double? maxWidth, double? maxHeight, int? quality) async {
            try {
              final XFile? pickedFile = await _picker.pickImage(
                source: source,
                maxWidth: maxWidth,
                maxHeight: maxHeight,
                imageQuality: quality,
              );
              setState(() {
                _setImageFileListFromFile(pickedFile);
              });
            } catch (e) {
              setState(() {
                _pickImageError = e;
              });
            }
          });
    }
  }

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

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

  Future<void> _disposeVideoController() async {
    if (_toBeDisposed != null) {
      await _toBeDisposed!.dispose();
    }
    _toBeDisposed = _controller;
    _controller = null;
  }
  //中间的提示文字
  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),
    );
  }
//中间的提示文字
  Widget _previewImages() {
    final Text? retrieveError = _getRetrieveErrorWidget();
    if (retrieveError != null) {
      return retrieveError;
    }
    if (_imageFileList != null) {
      return Semantics(
        label: 'image_picker_example_picked_images',
        child: ListView.builder(
          key: UniqueKey(),
          itemBuilder: (BuildContext context, int index) {
            // Why network for web?
            // See https://pub.dev/packages/image_picker#getting-ready-for-the-web-platform
            return Semantics(
              label: 'image_picker_example_picked_image',
              child: kIsWeb
                  ? Image.network(_imageFileList![index].path)
                  : Image.file(File(_imageFileList![index].path)),
            );
          },
          itemCount: _imageFileList!.length,
        ),
      );
    } 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,
      );
    }
  }
  //对中间提示文字进行了一次封装
  Widget _handlePreview() {
    if (isVideo) {
      return _previewVideo();
    } else {
      return _previewImages();
    }
  }

  Future<void> retrieveLostData() async {
    final LostDataResponse response = await _picker.retrieveLostData();
    if (response.isEmpty) {
      return;
    }
    if (response.file != null) {
      //如果是video
      if (response.type == RetrieveType.video) {
        isVideo = true;
        await _playVideo(response.file);
      }
      //是图片
      else {
        isVideo = false;
        setState(() {
          if (response.files == null) {
            _setImageFileListFromFile(response.file);
          } else {
            _imageFileList = response.files;
          }
        });
      }
    } else {
      _retrieveDataError = response.exception!.code;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      // appBar: AppBar(
      //   title: Text(widget.title!),
      // ),
      body: Center(
        child: !kIsWeb && defaultTargetPlatform == TargetPlatform.android
            ? FutureBuilder<void>(
          future: retrieveLostData(),//以后呈现的widget?
          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 _handlePreview();
              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,
                  );
                }
            }
          },
        )
            : _handlePreview(),
      ),
      /**右侧的浮游按钮*/
      floatingActionButton: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Semantics(//给UI加上语义，对一些语法分析器或者搜索引擎有帮助
            label: 'image_picker_example_from_gallery',
            child: FloatingActionButton(
              onPressed: () {
                isVideo = false;
                _onImageButtonPressed(ImageSource.gallery, context: context);
              },
              heroTag: 'image0',
              tooltip: 'Pick Image from gallery',
              child: const Icon(Icons.photo),
            ),
          ),
          Padding(
            padding: const EdgeInsets.only(top: 16.0),
            child: FloatingActionButton(
              onPressed: () {
                isVideo = false;
                _onImageButtonPressed(
                  ImageSource.gallery,
                  context: context,
                  isMultiImage: true,
                );
              },
              heroTag: 'image1',
              tooltip: 'Pick Multiple 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, context: context);
              },
              heroTag: 'image2',
              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;
  }

  Future<void> _displayPickImageDialog(
      BuildContext context, OnPickImageCallback onPick) async {
    return showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: const Text('Add optional parameters'),
            content: Column(
              children: <Widget>[
                TextField(
                  controller: maxWidthController,//该变量存储输入内容的值
                  keyboardType:
                  const TextInputType.numberWithOptions(decimal: true),
                  decoration: const InputDecoration(
                      hintText: 'Enter maxWidth if desired'),
                ),
                TextField(
                  controller: maxHeightController,
                  keyboardType:
                  const TextInputType.numberWithOptions(decimal: true),
                  decoration: const InputDecoration(
                      hintText: 'Enter maxHeight if desired'),
                ),
                TextField(
                  controller: qualityController,
                  keyboardType: TextInputType.number,
                  decoration: const InputDecoration(
                      hintText: 'Enter quality if desired'),
                ),
              ],
            ),
            actions: <Widget>[
              TextButton(
                child: const Text('CANCEL'),
                onPressed: () {
                  Navigator.of(context).pop();
                },
              ),
              TextButton(
                  child: const Text('PICK'),
                  onPressed: () {
                    final double? width = maxWidthController.text.isNotEmpty
                        ? double.parse(maxWidthController.text)
                        : null;
                    final double? height = maxHeightController.text.isNotEmpty
                        ? double.parse(maxHeightController.text)
                        : null;
                    final int? quality = qualityController.text.isNotEmpty
                        ? int.parse(qualityController.text)
                        : null;
                    onPick(width, height, quality);
                    Navigator.of(context).pop();
                  }),
            ],
          );
        });
  }
}

typedef OnPickImageCallback = void Function(
    double? maxWidth, double? maxHeight, int? quality);

class AspectRatioVideo extends StatefulWidget {
  const AspectRatioVideo(this.controller, {Key? key}) : super(key: key);

  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.isInitialized) {
      initialized = controller!.value.isInitialized;
      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();
    }
  }
}

效果图

主页面

挑选一张照片

正在播放视频

知识点补充

1. Future：Dart的异步对象，类似于JavaScript中的Promise
   1. 是一个异步操作返回的结果
   2. 是一个泛型类
   3. 官网说明

2. 
   Dart中的?学问：博客
   1. String?name ：表示可空类型
   2. String a = b ?? ‘hello’：b不为空，a赋值为b。b为Null，则a赋值为‘hello’
   3. b ??= ‘hello’：如果b为null则赋值为hello，否则不会改动
   4. a?.p a?.m()：如果a为空，则直接返回Null，不执行后面的操作
      2. a!.p 断言，表示a肯定不为null