Flutter:合并两个图像，并将其作为单个图像存储在本地存储中

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

class MergeImagesPage extends StatefulWidget {
  @override
  _MergeImagesPageState createState() => _MergeImagesPageState();
}

class _MergeImagesPageState extends State<MergeImagesPage> {
  File _image1;
  File _image2;
  File _mergedImage;

  Future<void> _pickImage(ImageSource source) async {
    final image = await ImagePicker().getImage(source: source);
    setState(() {
      if (_image1 == null) {
        _image1 = File(image.path);
      } else {
        _image2 = File(image.path);
      }
    });
  }

  Future<void> _mergeImages() async {
    if (_image1 != null && _image2 != null) {
      final image1 = img.decodeImage(_image1.readAsBytesSync());
      final image2 = img.decodeImage(_image2.readAsBytesSync());
      final mergedImage = img.Image(image1.width, image1.height);

      img.copyInto(mergedImage, image1, blend: false);
      img.copyInto(mergedImage, image2, blend: true);

      final directory = await getApplicationDocumentsDirectory();
      final path = '${directory.path}/merged_image.png';
      final mergedFile = File(path);

      await mergedFile.writeAsBytes(img.encodePng(mergedImage));

      setState(() {
        _mergedImage = mergedFile;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Merge Images'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            if (_mergedImage != null)
              Image.file(_mergedImage)
            else
              Text('No merged image'),
            SizedBox(height: 20),
            RaisedButton(
              onPressed: () => _pickImage(ImageSource.gallery),
              child: Text('Pick Image 1'),
            ),
            RaisedButton(
              onPressed: () => _pickImage(ImageSource.gallery),
              child: Text('Pick Image 2'),
            ),
            RaisedButton(
              onPressed: _mergeImages,
              child: Text('Merge Images'),
            ),
          ],
        ),
      ),
    );
  }
}