Unable to pass List<Uint8List>

[tnghieu]

@pragma('vm:entry-point')
void startProcessingImagesInBackground(List<List<Uint8List>> imageFiles) async {
  await FlutterIsolate.spawn(separateBatches, imageFiles);
}

@pragma('vm:entry-point')
void separateBatches(List<List<Uint8List>> imageFiles) async {
  for (List<Uint8List> images in imageFiles) {
    await flutterCompute(processBatch, images);
  }
}

@pragma('vm:entry-point')
Future<List<ResultObjectDetection>> processBatch(List<Uint8List> images) async {
  List<ResultObjectDetection> resultsForThisBatch = [];
  for (Uint8List image in images) {
    List<ResultObjectDetection> results =
        await objectDetectionModel.getImagePrediction(
      image,
      minimumScore: 0.75,
      preProcessingMethod: pt_model.PreProcessingMethod.native,
    );
    resultsForThisBatch.addAll(results);
  }
  return resultsForThisBatch;
}

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Invalid argument: is a Type: Uint8List

Unable to process this data with flutter_isolate. Can I only pass primitive types?

[nmfisher]

Reproducible on iOS simulator.

Also reproducible with pure Dart isolates:

main1.dart

import 'dart:isolate';
import 'dart:typed_data';

void main() async {
  await Isolate.spawnUri(Uri.parse('main2.dart'), [], <Uint8List>[
    Uint8List.fromList([1])
  ]);
  await Future.delayed(Duration(seconds: 5));
}

main2.dart

import 'dart:typed_data';

@pragma('vm:entry-point')
void main(List<String> args, Uint8List message) {
  print(args);
}

> dart run main1.dart 
Unhandled exception:
Invalid argument: is a Type: Uint8List
#0      Isolate._spawnUri (dart:isolate-patch/isolate_patch.dart:532:25)
#1      Isolate.spawnUri (dart:isolate-patch/isolate_patch.dart:459:7)
#2      main (package:flutter_isolate_example/main1.dart:5:17)
#3      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:297:19)
#4      _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

[nmfisher]

@tnghieu I doubt this is functioning correctly so I will file an issue against the dart-lang/sdk repository. If you need an immediate workaround, I suggest you pass things around as List<List<int>> rather than List<Uint8List>

https://github.com/dart-lang/sdk/issues/53890

[nmfisher]

Fix has been merged into the dartlang SDK, so wait for that to appear upstream and bump your SDK version number.

In the meantime, try sending as List<List> or wrapping with TransferableTypedData (suggested by Dart maintainers, I haven't actually tried that myself).