Flutter 'onCreate' overrides nothing

Question

I want to add some kotlin code on my flutter app. I add onCreate function on project_name/android/app/src/main/kotlin/com/example/app/MainActivity.kt.

This is my full MainActivity.kt

import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugins.GeneratedPluginRegistrant
import android.os.Environment
import android.net.Uri

import android.content.Intent

class MainActivity: FlutterActivity() {
    private val channel = "externalStorage";
    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, channel).setMethodCallHandler { call, result ->
            when (call.method) {
                "getExternalStorageDirectory" ->
                    result.success(Environment.getExternalStorageDirectory().toString())
                "getExternalStoragePublicDirectory" -> {
                    val type = call.argument<String>("type")
                    result.success(Environment.getExternalStoragePublicDirectory(type).toString())
                }
                else -> result.notImplemented()
            }
        }

    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        if (!Settings.canDrawOverlays(getApplicationContext())) {
            val myIntent = Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION)
            val uri: Uri = Uri.fromParts("package", getPackageName(), null)
            myIntent.setData(uri)
            startActivityForResult(myIntent, REQUEST_OVERLAY_PERMISSIONS)
            return
        }
    }
}

then I got this error on my build

'onCreate' overrides nothing
Unresolved reference: Settings
Unresolved reference: Settings
Unresolved reference:
REQUEST_OVERLAY_PERMISSIONS

Do I need to import some code?