Example of image_editor and extended_image.

example.dart

import 'dart:typed_data';

import 'package:extended_image/extended_image.dart';
import 'package:flutter/material.dart';
import 'package:image_editor/image_editor.dart';
import 'const/resource.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      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> {
  GlobalKey<ExtendedImageEditorState> editorKey = GlobalKey();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Column(
        children: <Widget>[
          AspectRatio(
            child: ExtendedImage.asset(
              R.ASSETS_123_JPG,
              extendedImageEditorKey: editorKey,
              mode: ExtendedImageMode.editor,
              fit: BoxFit.contain,
              initEditorConfigHandler: (state) {
                return EditorConfig(
                  maxScale: 8.0,
                  cropRectPadding: EdgeInsets.all(20.0),
                  hitTestSize: 20.0,
                  cropAspectRatio: 1,
                );
              },
            ),
            aspectRatio: 1,
          ),
          Expanded(child: Container()),
          Container(
            height: 50,
            child: Row(
              children: <Widget>[
                _buildIconButton(Icons.rotate_left, _rotateLeft),
                _buildIconButton(Icons.rotate_left, _rotateRight),
                _buildIconButton(Icons.flip, _flipHor),
                _buildIconButton(Icons.check, _crop),
              ],
            ),
          ),
        ],
      ),
    );
  }

  Widget _buildIconButton(IconData iconData, Function onTap) {
    return Expanded(
      child: IconButton(
        icon: Icon(iconData),
        onPressed: onTap,
      ),
    );
  }

  _rotateLeft() {
    editorKey.currentState.rotate(right: false);
  }

  _rotateRight() {
    editorKey.currentState.rotate();
  }

  _flipHor() {
    editorKey.currentState.flip();
  }

  _crop() async {
    final state = editorKey.currentState;
    final cropRect = state.getCropRect();
    final action = state.editAction;

    final rotateAngle = action.rotateAngle.toInt();
    final flipHorizontal = action.flipY;
    final flipVertical = action.flipX;
    final img = state.rawImageData;

    ImageEditorOption option = ImageEditorOption();

    if (action.needCrop) option.addOption(ClipOption.fromRect(cropRect));

    if (action.needFlip)
      option.addOption(
          FlipOption(horizontal: flipHorizontal, vertical: flipVertical));

    if (action.hasRotateAngle) option.addOption(RotateOption(rotateAngle));

    final start = DateTime.now();
    final result = await ImageEditor.editImage(
      image: img,
      imageEditorOption: option,
    );

    print("${DateTime.now().difference(start)} ：total time");

    showPreviewDialog(result);
  }

  void showPreviewDialog(Uint8List image) {
    showDialog(
      context: context,
      builder: (ctx) => GestureDetector(
        onTap: () => Navigator.pop(context),
        child: Container(
          color: Colors.grey.withOpacity(0.5),
          child: Center(
            child: SizedBox.fromSize(
              size: Size.square(200),
              child: Container(
                color: Colors.white,
                child: Image.memory(image),
              ),
            ),
          ),
        ),
      ),
    );
  }
}