MainActivity_channel.kt

//On Android
class MainActivity() : FlutterActivity() {

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    GeneratedPluginRegistrant.registerWith(this)
    MethodChannel(flutterView, "samples.flutter.io/battery").setMethodCallHandler { call, result ->
      if (call.method == "getBatteryLevel") {
        val batteryLevel = getBatteryLevel()

        if (batteryLevel != -1) {
          result.success(batteryLevel)
        } else {
          result.error("UNAVAILABLE", "Battery level not available.", null)
        }
      } else {
        result.notImplemented()
      }
    }
  }
}