EventChannel does not work inside an isolate #30332
Description
For some reason EventChannel does not listen for an events emitted from platform side if it runs within FlutterNativeView.runFromBundle isolate started as a part of android background service.
Keypoints
Plugin-like class implements simple MethodChannel and EventChannel.
Calling MethodChannel.invokeMethod emits counter on EventChannel.
class Plugin(registry: PluginRegistry, val label: String) {
@Volatile
private var sink: EventChannel.EventSink? = null
private val counter = AtomicInteger()
init {
registry.registrarFor("isolate").apply {
MethodChannel(messenger(), "methods").setMethodCallHandler { methodCall, result ->
sink?.success(hashMapOf(
"label" to label,
"counter" to counter.incrementAndGet()
))
Log.d("PLUGIN", "Call ${methodCall.method} from $label")
result.success(null)
}
EventChannel(messenger(), "events").setStreamHandler(object : EventChannel.StreamHandler {
override fun onListen(p0: Any?, s: EventChannel.EventSink?) {
sink?.endOfStream()
sink = s
}
override fun onCancel(p0: Any?) {
sink?.endOfStream()
sink = null
}
})
}
}
}
Dart handler use MethodChannel and EventChannel to periodicaly call method and waiting any data on event channel to arrive.
void platformChannels() {
print("Start platform channels test");
MethodChannel pluginMethods = const MethodChannel('methods');
EventChannel pluginEvents = const EventChannel('events');
pluginEvents.receiveBroadcastStream().listen((data) {
print(data);
});
Timer.periodic(Duration(seconds: 1), (timer) {
pluginMethods.invokeMethod("tick", {});
});
}
Main activity startup code register the Plugin-like class and start android service
Plugin(this,"Activity")
startService(Intent(this,PluginService::class.java))
Service startup code create new dart isolate with backgound FlutterNativeView with dart entrypoint set to platformChannels on main.dart
override fun onCreate() {
super.onCreate()
FlutterMain.startInitialization(this)
FlutterMain.ensureInitializationComplete(this, null)
bgView = FlutterNativeView(this, true)
Plugin(bgView.pluginRegistry, "Service")
bgView.runFromBundle(FlutterRunArguments().apply {
bundlePath = FlutterMain.findAppBundlePath(this@PluginService)
entrypoint = "platformChannels"
})
}
Finnaly when app is runnung only Activity bound dart code works as expected. Service bound dart code never prints data on listen closure.
Steps to Reproduce
git clone https://github.com/softkot/flutter_isolate
cd flutter_isolate
Connect android device or an emulator and run
flutter run
Application logs
produced
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 2}
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 3}
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 4}
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 5}
expected
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 2}
I/flutter (25664): {label: Service, counter: 2}
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 3}
I/flutter (25664): {label: Service, counter: 3}
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 4}
I/flutter (25664): {label: Service, counter: 4}
D/PLUGIN (25664): Call tick from Service
D/PLUGIN (25664): Call tick from Activity
I/flutter (25664): {label: Activity, counter: 5}
I/flutter (25664): {label: Service, counter: 5}
Flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, v1.2.1, on Linux, locale ru_RU.UTF-8)
[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
[✓] Android Studio (version 3.3)
[✓] IntelliJ IDEA Ultimate Edition (version 2019.1)
[✓] Connected device (1 available)
• No issues found!