Android onResume() method equivalent in Flutter

You can use the WidgetsBindingObserver and check the AppLifeCycleState like this example:

class YourWidgetState extends State<YourWidget> with WidgetsBindingObserver {

  @override
  void initState() {
    WidgetsBinding.instance?.addObserver(this);
    super.initState();
  }

 
  @override
  void dispose() {
    WidgetsBinding.instance?.removeObserver(this);
    super.dispose();
  }
  

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
       //do your stuff
    }
  }
}

Take in mind that It will called every time you open the app or go the background and return to the app. (if your widget is active)

If you just want a listener when your Widget is loaded for first time, you can listen using addPostFrameCallback, like this example:

class YourWidgetState extends State<YourWidget> {

  _onLayoutDone(_) {
    //do your stuff
  }

  @override
  void initState() {
    WidgetsBinding.instance?.addPostFrameCallback(_onLayoutDone);
    super.initState();
  } 

}

Info : https://docs.flutter.io/flutter/widgets/WidgetsBindingObserver-class.html

Update: Null safety compliance