Application.kt

import android.app.Application
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.embedding.engine.FlutterEngineCache
import io.flutter.embedding.engine.dart.DartExecutor

class Application : Application() {

    override fun onCreate() {
        super.onCreate()

        // app initializations...

        passcodeFlutterEngine = FlutterEngine(this)
        passcodeFlutterEngine.dartExecutor.executeDartEntrypoint(
            DartExecutor.DartEntrypoint.createDefault()
        )
        FlutterEngineCache
            .getInstance()
            .put("passcodeFlutterEngine", passcodeFlutterEngine)

        informationTabFlutterEngine = FlutterEngine(this)
        informationTabFlutterEngine.dartExecutor.executeDartEntrypoint(
            DartExecutor.DartEntrypoint.createDefault()
        )

        FlutterEngineCache
            .getInstance()
            .put("informationTabFlutterEngine", informationTabFlutterEngine)

        qrcodeFlutterEngine = FlutterEngine(this)
        qrcodeFlutterEngine.dartExecutor.executeDartEntrypoint(
            DartExecutor.DartEntrypoint.createDefault()
        )

        FlutterEngineCache
            .getInstance()
            .put("qrcodeFlutterEngine", qrcodeFlutterEngine)

    }

    companion object {
        lateinit var context: Context
        lateinit var passcodeFlutterEngine : FlutterEngine
        lateinit var informationTabFlutterEngine : FlutterEngine
        lateinit var qrcodeFlutterEngine : FlutterEngine
    }
}