画布未在Flutter中绘制图像

Question

我正在尝试使用Canvas在图像上绘制一个矩形，我能够绘制一个矩形，但是该图像未被绘制。使用CustomPainter时，会绘制图像，但无法使用PictureRecorder捕获CustomPainter。

_makeImage() async {
    var byteData = await widget.file.readAsBytes();

    var codec = await ui.instantiateImageCodec(byteData);
    var nextFrame = await codec.getNextFrame();
    image = nextFrame.image;

    ui.PictureRecorder pictureRecorder = ui.PictureRecorder();
    Canvas canvas = new Canvas(pictureRecorder, Rect.fromPoints(Offset(0.0, 0.0), Offset(image.width.toDouble(), image.height.toDouble())));
    RectanglePainter rectanglePainter = RectanglePainter(image: image);
    rectanglePainter.paint(canvas, Size(image.width.toDouble(), image.height.toDouble()));
    canvas.drawImage(image, Offset(0.0, 0.0), Paint()..color = Colors.grey);
    canvas.drawRect(Rect.fromPoints(Offset(0.0, 0.0), Offset(image.width.toDouble() - 200.0, 200.0)), Paint()..color = Colors.green);
    var pngImage = await pictureRecorder
        .endRecording()
        .toImage(image.width, image.height)
        .toByteData(format: ui.ImageByteFormat.png);
    Directory directory = await getTemporaryDirectory();
    File pngFile = File(join(directory.path, "image.png"));
    if (await pngFile.exists()) {
      await pngFile.delete();
      await pngFile.create();
    }
    print(pngFile.path);
    await pngFile.writeAsBytes(pngImage.buffer.asUint8List(pngImage.offsetInBytes, pngImage.lengthInBytes));

    print(await pngFile.length());
    imageFile = pngFile;
    print('Image Update');
    setState(() {});
  }