如何在flutter中向图像添加文本

dependencies:
  flutter:
    sdk: flutter
  flutter_image:
  image_picker:
  path_provider:

import 'package:flutter/material.dart';
import 'package:flutter_image/flutter_image.dart';
import 'package:image_picker/image_picker.dart';
import 'package:path_provider/path_provider.dart';

class ImageWithText extends StatefulWidget {
  @override
  _ImageWithTextState createState() => _ImageWithTextState();
}

class _ImageWithTextState extends State<ImageWithText> {
  File _image;
  String _text = '';

  Future getImage() async {
    var image = await ImagePicker.pickImage(source: ImageSource.gallery);

    setState(() {
      _image = image;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Add Text to Image'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            _image == null
                ? Text('No image selected.')
                : Image.file(_image),
            SizedBox(height: 20),
            TextField(
              onChanged: (value) {
                setState(() {
                  _text = value;
                });
              },
              decoration: InputDecoration(
                hintText: 'Enter text',
              ),
            ),
            SizedBox(height: 20),
            RaisedButton(
              onPressed: getImage,
              child: Text('Select Image'),
            ),
            SizedBox(height: 20),
            RaisedButton(
              onPressed: () async {
                final directory = await getApplicationDocumentsDirectory();
                final imagePath = '${directory.path}/image_with_text.png';

                await drawTextOnImage(_image.path, imagePath, _text);

                // Use the resulting image with text
                // e.g. upload to server or display it
              },
              child: Text('Add Text'),
            ),
          ],
        ),
      ),
    );
  }

  Future<void> drawTextOnImage(
      String imagePath, String outputPath, String text) async {
    final image = NetworkImage(imagePath);
    final imageBytes = await image.resolve(ImageConfiguration()).toByteData();
    final imageCodec = await instantiateImageCodec(imageBytes.buffer.asUint8List());
    final frameInfo = await imageCodec.getNextFrame();
    final imageWidget =
        await flutterImage.instantiateImageCodec(frameInfo.image).then((value) => value.getNextFrame()).then((value) => value.image);

    final recorder = ui.PictureRecorder();
    final canvas = Canvas(recorder);

    canvas.drawImage(imageWidget, Offset.zero, Paint());

    final textStyle = ui.TextStyle(color: Colors.black, fontSize: 20);
    final paragraphStyle = ui.ParagraphStyle(textAlign: TextAlign.center);
    final paragraphBuilder =
        ui.ParagraphBuilder(ui.ParagraphStyle(textAlign: TextAlign.center))
          ..pushStyle(textStyle)
          ..addText(text);
    final paragraph = paragraphBuilder.build()
      ..layout(ui.ParagraphConstraints(width: imageWidget.width.toDouble()));

    canvas.drawParagraph(
        paragraph,
        Offset((imageWidget.width - paragraph.width) / 2,
            imageWidget.height.toDouble() - 50));

    final picture = recorder.endRecording();
    final imageWithText = await picture.toImage(
        imageWidget.width.toInt(), imageWidget.height.toInt());
    final pngBytes = await imageWithText.toByteData(format: ui.ImageByteFormat.png);

    final output = File(outputPath);
    await output.writeAsBytes(pngBytes.buffer.asUint8List());
  }
}

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Add Text to Image',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: ImageWithText(),
    );
  }
}