Can I use Async inside Dart Isolate ??? its not working - flutter

Question

I am using ImageEditor package to merge different images. below is my code. its working perfectly fine without using Isolate, when i use it with isolate, i get null error.
Working code without Isolate
startEditing() async {
for (var i = 0; i < image1.length || i == 0; i++) {
if (image1.isNotEmpty) {
img1 = await File(image1[i].path).readAsBytes();
}
for (var i = 0; i < image2.length || i == 0; i++) {
if (image2.isNotEmpty) {
img2 = await File(image2[i].path).readAsBytes();
}
final ImageEditorOption optionGroup = ImageEditorOption();
optionGroup.outputFormat = const OutputFormat.png(100);
optionGroup.addOptions([
MixImageOption(
x: 0,
y: 0,
width: 1000,
height: 1000,
target: MemoryImageSource(img1),
),
MixImageOption(
x: 0,
y: 0,
width: 1000,
height: 1000,
target: MemoryImageSource(img2),
),
]);
try {
final Uint8List? result = await ImageEditor.editImage(
image: mainImg, imageEditorOption: optionGroup);
if (result == null) {
image = null;
} else {
await saveImage(result, index);
setState(() {
image = MemoryImage(result);
index++;
});
}
} catch (e) {
print(e);
}
}
}
}
Code with Isolate not working
startEditing(SendPort sendPort) async {
for (var i = 0; i < image1.length || i == 0; i++) {
if (image1.isNotEmpty) {
img1 = await File(image1[i].path).readAsBytes();
}
for (var i = 0; i < image2.length || i == 0; i++) {
if (image2.isNotEmpty) {
img2 = await File(image2[i].path).readAsBytes();
}
final ImageEditorOption optionGroup = ImageEditorOption();
optionGroup.outputFormat = const OutputFormat.png(100);
optionGroup.addOptions([
MixImageOption(
x: 0,
y: 0,
width: 1000,
height: 1000,
target: MemoryImageSource(img1),
),
MixImageOption(
x: 0,
y: 0,
width: 1000,
height: 1000,
target: MemoryImageSource(img2),
),
]);
try {
final Uint8List? result = await ImageEditor.editImage(
image: mainImg, imageEditorOption: optionGroup);
if (result == null) {
image = null;
} else {
await saveImage(result, index);
image = MemoryImage(result);
index++;
sendPort.send(image);
}
} catch (e) {
print(e);
}
}
}
}
saveImage method
Future<String> saveImage(Uint8List bytes, int i) async {
final name = '${filenames[i]}';
final result = await ImageGallerySaver.saveImage(bytes, name: name);
print(result);
return result['filePath'];
}
Receiving in main thread
getImageas() async {
ReceivePort receiverPort =
ReceivePort();
final isolate =
await Isolate.spawn(startEditing, receiverPort.sendPort);
receiverPort.listen((data) {
print('Receiving: ' + data + ', ');
});
}
I get this error:
I/flutter (21937): Null check operator used on a null value
in this line:
final Uint8List? result = await ImageEditor.editImage(
image: mainImg, imageEditorOption: optionGroup);
I am sure that img1, img2, mainImg, image1, image2 values are not null... check 1000 times. I have also used flutter compute, and same result.

Answer 1

Flutter plugins that call into native code (such as image_editor) do not work in isolates spawned by Isolate.spawn.
The flutter_isolate package spawns isolates from native code for this reason. You should be able to use it to call image_editor in an isolate. (Disclaimer: I've never used flutter_isolate.)