java.lang.RuntimeException: Methods marked with @UiThread must be executed on the main thread.

[SamuelAG]

I tried to use your example but it is giving a exception:

E/AndroidRuntime(30424): FATAL EXCEPTION: Thread-5 E/AndroidRuntime(30424): Process: dev.bessems.usbserialexample, PID: 30424 E/AndroidRuntime(30424): java.lang.RuntimeException: Methods marked with @UiThread must be executed on the main thread. Current thread: Thread-5 E/AndroidRuntime(30424): at io.flutter.embedding.engine.FlutterJNI.ensureRunningOnMainThread(FlutterJNI.java:794) E/AndroidRuntime(30424): at io.flutter.embedding.engine.FlutterJNI.dispatchPlatformMessage(FlutterJNI.java:684) E/AndroidRuntime(30424): at io.flutter.embedding.engine.dart.DartMessenger.send(DartMessenger.java:80) E/AndroidRuntime(30424): at io.flutter.embedding.engine.dart.DartExecutor.send(DartExecutor.java:174) E/AndroidRuntime(30424): at io.flutter.view.FlutterNativeView.send(FlutterNativeView.java:144) E/AndroidRuntime(30424): at io.flutter.plugin.common.EventChannel$IncomingStreamRequestHandler$EventSinkImplementation.success(EventChannel.java:226) E/AndroidRuntime(30424): at dev.bessems.usbserial.UsbSerialPortAdapter$1.onReceivedData(UsbSerialPortAdapter.java:60) E/AndroidRuntime(30424): at com.felhr.usbserial.UsbSerialDevice$WorkerThread.onReceivedData(UsbSerialDevice.java:361) E/AndroidRuntime(30424): at com.felhr.usbserial.UsbSerialDevice$WorkerThread.doRun(UsbSerialDevice.java:336) E/AndroidRuntime(30424): at com.felhr.usbserial.AbstractWorkerThread.run(AbstractWorkerThread.java:21)

When I remove this part of the code, the error disappears _subscription = _transaction.stream.listen((String line) { setState(() { _serialData.add(Text(line)); if (_serialData.length > 20) { _serialData.removeAt(0); } }); }); But i need to receive data from UART.

Flutter Doctor: Doctor summary (to see all details, run flutter doctor -v): [√] Flutter (Channel stable, v1.7.8+hotfix.3, on Microsoft Windows [versão 10.0.17134.829], locale pt-BR) [√] Android toolchain - develop for Android devices (Android SDK version 28.0.3) [!] Android Studio (version 3.4) X Flutter plugin not installed; this adds Flutter specific functionality. X Dart plugin not installed; this adds Dart specific functionality. [√] VS Code (version 1.36.0) [√] Connected device (2 available)

Any ideia what is might be?

[Eternali]

I had this issue too, it's been cropping up in a lot of plugins recently. I think it has to do with plugins needing to communicate with dart on the main thread rather than some background thread. The workaround to fix this is basically to edit UsbSerialPortAdapter.java to replace this:

if ( m_EventSink != null ) {
    m_EventSink.success(arg0);
}

with this:

if ( m_EventSink != null ) {
    m_handler.post(new Runnable() {
        @Override
        public void run() {
            m_EventSink.success(arg0);
        }
    });
}

Where m_handler is set in the constructor to be m_handler = new Handler(Looper.getMainLooper());.

Note: you have to add these imports too

import android.os.Handler;
import android.os.Looper;

I'll have a PR up for this shortly. Hope it helps!

[altera2015]

Thanks for the PR, it's pulled and published!