a example for flutter compress

main.dart

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

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;
  String _retrieveDataError;

  ImageProvider provider;

  void _onImageButtonPressed(ImageSource source) async {
    try {
      _imageFile = await ImagePicker.pickImage(source: source);
      if (_imageFile == null || _imageFile.path == null) {
        print("The pick image is null.");
        return;
      }
      print("pickImageSuccess.");
      print('$_imageFile');
      var tmpDir = await path_provider.getTemporaryDirectory();
      var targetName = DateTime.now().millisecondsSinceEpoch;
      File compressFile = await FlutterImageCompress.compressAndGetFile(
        _imageFile.path,
        "${tmpDir.absolute.path}/$targetName.jpg",
        quality: 50,
        minWidth: 500,
        minHeight: 500,
      );
      if (compressFile != null) {
        this.provider = FileImage(compressFile);
      }
      print("compress success");
    } catch (e) {
      print("pickImageError, error is $e");
    }
    setState(() {});
  }

  Widget _buildWidget() {
    if (provider == null) {
      return Text("You have not yet picked an image.");
    }
    final Text retrieveError = _getRetrieveErrorWidget();
    if (retrieveError != null) {
      return retrieveError;
    }
    return Image(
      image: provider,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: _buildWidget(),
      ),
      floatingActionButton: Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          FloatingActionButton(
            onPressed: () {
              _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: () {
                _onImageButtonPressed(ImageSource.camera);
              },
              heroTag: 'image1',
              tooltip: 'Take a Photo',
              child: const Icon(Icons.camera_alt),
            ),
          ),
        ],
      ),
    );
  }

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

pubspec.yaml

name: a_example_for_compress
description: A new Flutter project.

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: '>=2.1.0 <3.0.0'

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  image_picker: 0.4.12+1
  flutter_image_compress: ^0.5.2
  path_provider: ^1.1.0

dev_dependencies:
  flutter_test:
    sdk: flutter

# For information on the generic Dart part of this file, see the
# following page: https://www.dartlang.org/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:
  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true
  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg
  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.
  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages
  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages