Either hide or heavily discourage the use of `reference` and `fromRef`

[HosseinYousefi]

Although safe methods like castTo are provided, users might still use fromRef and .reference to manually cast objects (see #970), keep references without properly managing their lifecycle, etc. Therefore, JniGen generated code should heavily discourage the use of these inner workings and eventually hide them. Right now, we need references to send these finalizable JObjects between multiple isolates, but dart-lang/sdk#55062 will make these objects sendable.

cc/ @dcharkes

[yanshouwang]

Hello, @HosseinYousefi
I found here you mentioned that we can send a JObject between isolates, but when I send the reference to another isolate and call formRef constructor, the first time it's ok to do this, but when I send this reference again, the fromRef method will throw error like this:

signal 6 (SIGABRT), code -1 (SI_QUEUE), fault addr --------
Abort message: 'JNI DETECTED ERROR IN APPLICATION: JNI ERROR (app bug): jobject is an invalid global reference: 0x357a (deleted reference at index 427)

Is it possible for us to send a JObject to another isolate?

[HosseinYousefi]

I have explained one way to send them here: #970 (comment)

[yanshouwang]

@HosseinYousefi
Thank you for your answer, that's works like a charm~

[HosseinYousefi]

@HosseinYousefi Thank you for your answer, that's works like a charm~

With the newly released 0.8.0, you can skip the manual way (in Dart's main branch – not yet in stable) and just pass JObjects around as you would with any other object.

[yanshouwang]

With the newly released 0.8.0, you can skip the manual way (in Dart's main branch – not yet in stable) and just pass JObjects around as you would with any other object.

@HosseinYousefi , I have updated to 0.8.0, when I pass the JObject to an isolate, the error throws, I use the flutter stable channel now.

E/flutter (13009): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Invalid argument(s): Illegal argument in isolate message: (object is a Pointer)
E/flutter (13009):  <- Instance of 'JGlobalReference' (from package:jni/src/jreference.dart)
E/flutter (13009):  <- $type in Instance of 'BarcodeScanner' (from package:hybrid_vision_android/src/jni.g.dart)
E/flutter (13009):  <- scanner in Instance of '_DetectCommand' (from package:hybrid_vision_android/src/barcode_detection.dart)
E/flutter (13009): 
E/flutter (13009): #0      _SendPort._sendInternal (dart:isolate-patch/isolate_patch.dart:250:43)
E/flutter (13009): #1      _SendPort.send (dart:isolate-patch/isolate_patch.dart:231:5)
E/flutter (13009): #2      AndroidBarcodeDetector.detect (package:hybrid_vision_android/src/barcode_detection.dart:51:14)
E/flutter (13009): <asynchronous suspension>
E/flutter (13009): #3      _BarcodeDetectionViewState.buildDetectView.<anonymous closure>.<anonymous closure> (package:hybrid_vision_android_example/views/barcode_detection_view.dart:173:38)
E/flutter (13009): <asynchronous suspension>
E/flutter (13009):