Null Safety on exportImage

[ccc-dvansevenant]

Thanks for this library, and starting to migrate it to null safety.

I am using image_painter: ^1.0.0-nullsafety.0.

My project is set with:

environment:
  sdk: ">=2.12.0 <3.0.0"

As I was implementing image_painter in my project, I was having issues with exportImage.

It kept complaining about ByteData, and then buffer. Eventually I hit upon this combination:

  ///Generates [Uint8List] of the [ui.Image] generated by the [renderImage()] method.
  ///Can be converted to image file by writing as bytes.
  Future<Uint8List?> exportImage() async {
    ui.Image _image;
    if (widget.isSignature) {
      final _boundary = _repaintKey.currentContext!.findRenderObject()
          as RenderRepaintBoundary;
      _image = await _boundary.toImage(pixelRatio: 3);
    } else if (widget.byteArray != null && _paintHistory.isEmpty) {
      return widget.byteArray;
    } else {
      _image = await _renderImage();
    }
    final byteData = await (_image.toByteData(format: ui.ImageByteFormat.png) as FutureOr<ByteData?>);
    return byteData?.buffer.asUint8List();

Note the last 2 lines, specifically.

I don't know if it's correct or not, but thought I'd pass it along in case it helps.

I'm still learning, very slowly, so it's certainly possible this could be done better.

[lively-bigyan]

Thank you for opening up the issue and bringing it to my attention. I will definitely take a look at it.

[lively-bigyan]

I am not able to reproduce the issue. It would be much faster and easier for us to fix the issue if you could provide the following informations.

• flutter version and device,
• Steps to reproduce and
• error log

[ccc-dvansevenant]

Sorry for the delay. Thanks for the quick reply. Here's my discovery process. Might be a bit verbose, but I want to cover the bases in case I did something wrong.

Using Android Studio 4.2.2 (was 4.2.1 when this started)
Flutter v2.2.3 (was 2.2.2)
Mac OS X Catalina

• Create new flutter project

• Ensure pubspec.yml has sdk: ">=2.12.0 <3.0.0"

• Using image_painter: ^1.0.0-nullsafety.0

• Replace main.dart code with the example code from here: https://pub.dev/packages/image_painter/versions/1.0.0-nullsafety.0/example

• Note error regarding missing file assets/sample.jpg :

E/flutter (16431): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Unable to load asset: assets/sample.jpg
E/flutter (16431): #0      PlatformAssetBundle.load (package:flutter/src/services/asset_bundle.dart:224:7)
E/flutter (16431): <asynchronous suspension>
E/flutter (16431): #1      ImagePainterState._resolveAndConvertImage (package:image_painter/src/paint_over_image.dart:211:19)
E/flutter (16431): <asynchronous suspension>
E/flutter (16431): 

• fix by creating /assets, adding a file called sample.jpg and editing pubspec.yml and adding:

assets:
  - sample.jpg

(Really, a non-issue, since that part will be replaced by loading an actual image)

• Run app on emulator and draw, then save.

• Note error message about Future<Uint8List?> not being a subtype of <FutureOr<Uint8List>

E/flutter ( 4984): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: type 'Future<Uint8List?>' is not a subtype of type 'FutureOr<Uint8List>' in type cast 

From the saveImage function:

void saveImage() async {  
final image =  
    await (_imageKey.currentState!.exportImage() as FutureOr<Uint8List>);  
final directory = (await getApplicationDocumentsDirectory()).path;

The FutureOr is not liked.
I removed it in my code.
The line became:

final Uint8List? image = await (_imageKey.currentState!.exportImage());

Which then causes an issue with image:

final imgFile = File('$fullPath');  
imgFile.writeAsBytesSync(image);  
ScaffoldMessenger.of(context).showSnackBar(

So, add a null check:

imgFile.writeAsBytesSync(image!);

Running again:

E/flutter ( 6142): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: type 'Future<ByteData?>' is not a subtype of type 'FutureOr<ByteData>' in type cast
E/flutter ( 6142): #0      ImagePainterState.exportImage (package:image_painter/src/paint_over_image.dart:464:5)
E/flutter ( 6142): <asynchronous suspension>
E/flutter ( 6142): #1      _ImagePainterExampleState.saveImage (package:image_painter_null_safety_test/main.dart:57:30)
E/flutter ( 6142): <asynchronous suspension>
E/flutter ( 6142): 

Modifying paint_over_image.dart line 463-464 gets rid of that error:

final byteData = await (\_image.toByteData(format: ui.ImageByteFormat.png)  
as FutureOr<ByteData?>);

But introduces an error about buffer:

/usr/local/Caskroom/flutter/2.0.4/flutter/.pub-cache/hosted/pub.dartlang.org/image_painter-1.0.0-nullsafety.0/lib/src/paint_over_image.dart:465:21: Error: Property 'buffer' cannot be accessed on 'ByteData?' because it is potentially null.
 - 'ByteData' is from 'dart:typed_data'.
Try accessing using ?. instead.
    return byteData.buffer.asUint8List();
                    ^^^^^^

So, modifying 465, as suggested:

return byteData?.buffer.asUint8List();

Seems to make it all work without complaint. But, again, do not know if it is the right way.

[dchrzanowski]

Flutter 2.5.1, dart 2.14.2

@lively-bigyan

I'm working with this library at the moment and can confirm that I have the same issue as @ccc-dvansevenant. Can also confirm that changing the paint_over_image.dart file (line 464/465) from:

final byteData = await (_image.toByteData(format: ui.ImageByteFormat.png)
    as FutureOr<ByteData>);
return byteData.buffer.asUint8List();

To:

final byteData = await (_image.toByteData(format: ui.ImageByteFormat.png)
    as FutureOr<ByteData?>);
return byteData?.buffer.asUint8List();

Does fix the problem.

Should I create a PR or are you ok fixing this @lively-bigyan ?

[lively-bigyan]

@dchrzanowski Thank you for the tests and the solution. I am currently working on some new features of the package so I couldn't push the fixes sooner. I shall fix it today.

[lively-bigyan]

On second thought, I just realized that I had it fixed on 0.4.0. Have you guys tried that version? @dchrzanowski @ccc-dvansevenant

[ccc-dvansevenant]

On second thought, I just realized that I had it fixed on 0.4.0. Have you guys tried that version? @dchrzanowski @ccc-dvansevenant

I've had to set aside that part of my project for a while, so I haven't updated anything. I'll try to have a look soon. Thanks!

[dchrzanowski]

@lively-bigyan I did not realize that 0.4.0 was null safety ready. I'll check it out tomorrow morning so.

[dchrzanowski]

On second thought, I just realized that I had it fixed on 0.4.0. Have you guys tried that version? @dchrzanowski @ccc-dvansevenant

0.4.0 works like a charm! Thanks @lively-bigyan!

[lively-bigyan]

Not a problem. Glad it helped.