[SOLVED] Flutter Dart - Calling sqflite function in Isolate causes error

I have a sqflite database that works, unit tests work. I want to call a sqflite method in onTap method. I understand I cannot execute the sqflite function in the main UI thread (Flutter tells me that at runtime). So I created an Isolate to call the sqflite function, which gives a different error. The Isolate works if I don't call the sqflite function, works if I just return a bool. Here is the code and exception - thanks for any suggestions:

Snippet from UI

    Widget loginButton(BuildContext context) {
    return Expanded(
      child: Padding(
        padding: const EdgeInsets.only(left: 20.0, right: 5.0, top: 20.0, bottom: 0.0),
        child: GestureDetector(
          onTap: () {
            if (emailController.text.length > 1 && passwordController.text.length > 7) {
              /// Find user. Then...
              doCheckIfFoundUser(emailController.text.trim(), passwordController.text);
            } else {
              printUserNotFound();
            }

          },
        child: buttonContainer(Colors.indigo, "Login", 20.0),
        ),
      ),
    );

Method called from UI

doCheckIfFoundUser(String email, String password) async {
    var result;
    List<String> emailPasswordList = new List();
    emailPasswordList.add(email);
    emailPasswordList.add(password);
    var receivePort = new ReceivePort();
    Isolate.spawn(callbackFunction, receivePort.sendPort);
    SendPort sendPort = await receivePort.first;
    var ans = await sendReceive(sendPort, emailPasswordList);
    setState(() {
      result = ans;
      print("The value is $result - please do your thing");
    });
}

Isolate Callback

static void callbackFunction(SendPort callerSendPort) async {

    ReceivePort newIsolateReceivePort = ReceivePort();


    callerSendPort.send(newIsolateReceivePort.sendPort);
    var msg = await newIsolateReceivePort.first;
    List<String> emailPasswordList = msg[0];

    print("email: ${emailPasswordList[0]}, password: ${emailPasswordList[1]}");

    bool foundUser = await searchForUser(emailPasswordList[0], emailPasswordList[1]);
    SendPort replyPort = msg[1];
    replyPort.send(foundUser);
}

Future sendReceive(SendPort send, message) {
  ReceivePort receivePort = ReceivePort();
  send.send([message, receivePort.sendPort]);
  return receivePort.first;}

I/flutter ( 2073): email: email, password: Passw0rd

E/flutter ( 2073): [ERROR:flutter/runtime/dart_isolate.cc(805)] Unhandled exception:

E/flutter ( 2073): error: native function 'Window_sendPlatformMessage' (4 arguments) cannot be found

E/flutter ( 2073): #0 Window.sendPlatformMessage (dart:ui/window.dart:1089:9)

E/flutter ( 2073): #1 _DefaultBinaryMessenger._sendPlatformMessage (package:flutter/src/services/binary_messenger.dart:85:15)

E/flutter ( 2073): #2 _DefaultBinaryMessenger.send (package:flutter/src/services/binary_messenger.dart:129:12)

E/flutter ( 2073): #3 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:309:51)

E/flutter ( 2073):

E/flutter ( 2073): #4 invokeMethod (package:sqflite/src/sqflite_impl.dart:18:34)

E/flutter ( 2073):

E/flutter ( 2073): #5 SqfliteDatabaseFactoryImpl.invokeMethod (package:sqflite/src/factory_impl.dart:33:7)

E/flutter ( 2073): #6 _SqfliteDatabaseFactoryImpl&Object&SqfliteDatabaseFactoryMixin.safeInvokeMethod. (package:sqflite/src/factory_mixin.dart:22:35)

E/flutter ( 2073): #7 wrapDatabaseException (package:sqflite/src/exception_impl.dart:7:34) E/flutter ( 2073): .

E/flutter ( 2073): #8 SqfliteDatabaseFactoryImpl.wrapDatabaseException (package:sqflite/src/factory_impl.dart:29:7).

E/flutter ( 2073): #9 _SqfliteDatabaseFactoryImpl&Object&SqfliteDatabaseFactoryMixin.safeInvokeMethod (package:sqflite/src/factory_mixin.dart:22:7). E/flutter ( 2073): #10 _SqfliteDatabaseFactoryImpl&Object&SqfliteDatabaseFactoryMixin.getDatabasesPath (package:sqflite/src/factory_mixin.dart:136:17). E/flutter ( 2073): E/flutter ( 2073): #11 getDatabasesPath. (package:sqflite/sqflite.dart:166:54) E/flutter ( 2073): #12 UsersSqflite.init (package:himrepo/controller/users_database.dart:20:47). E/flutter ( 2073): . E/flutter ( 2073): #13 _LoginPageState.searchForUser. (package:himrepo/ui/login.dart:268:24). E/flutter ( 2073): . E/flutter ( 2073): #14 _LoginPageState.callbackFunction(package:himrepo/ui/login.dart:166:28). E/flutter ( 2073): . E/flutter ( 2073): #15 _startIsolate.. (dart:isolate-patch/isolate_patch.dart:304:17). E/flutter ( 2073): #16 _RawReceivePortImpl._handleMessage(dart:isolate-patch/isolate_patch.dart:172:12).

Executing Sqflite method directly gives

E/AndroidRuntime( 6628): FATAL EXCEPTION: Sqflite
E/AndroidRuntime( 6628): java.lang.RuntimeException: Methods marked with @UiThread must be executed on the main thread. Current thread: Sqflite
E/AndroidRuntime( 6628):    at io.flutter.embedding.engine.FlutterJNI.ensureRunningOnMainThread(FlutterJNI.java:794)
E/AndroidRuntime( 6628):    at io.flutter.embedding.engine.FlutterJNI.invokePlatformMessageResponseCallback(FlutterJNI.java:727)
E/AndroidRuntime( 6628):    at io.flutter.embedding.engine.dart.DartMessenger$Reply.reply(DartMessenger.java:140)
E/AndroidRuntime( 6628):    at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler$1.success(MethodChannel.java:225)
E/AndroidRuntime( 6628):    at com.tekartik.sqflite.SqflitePlugin$6.run(SqflitePlugin.java:778)
E/AndroidRuntime( 6628):    at android.os.Handler.handleCallback(Handler.java:873)
E/AndroidRuntime( 6628):    at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 6628):    at android.os.Looper.loop(Looper.java:193)
E/AndroidRuntime( 6628):    at android.os.HandlerThread.run(HandlerThread.java:65)