MyFlutterActivity.kt

import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel

class MyFlutterActivity : FlutterActivity() {

    private val CHANNEL = "com.example.myflutterapp/data"
    val token = "dummy123"

    override fun getCachedEngineId(): String {
        return "my_engine_id"
    }

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
                call, result ->
            if (call.method == "getUserToken") else {
                result.notImplemented()
            }

            if (!token.isNullOrEmpty()) {
                result.success(token)
            } else {
                result.error("UNAVAILABLE", "Battery level not available.", null)
            }
        }
    }
}