[Solved] Error: setState() or markNeedsBuild() called during build error in a Stateless Widget

Hi stevediaz933,

This error happens when you try to show a snack bar or alert dialog before the completion of the widget build.

The showDialog method is called inside widget build method, which causes the run time error.

Widget build(BuildContext context) {
  showDialog(
    context: context,
    builder: (BuildContext context) {
        return AlertDialog(
          title: Text("How are you?"),
        );
  }); //Error: setState() or markNeedsBuild() called during build.

  return Scaffold(
        body: Center(
          child: Text("Hello World")      
        )
  );
} 

You must wrap your code using Future.delayed.

Widget build(BuildContext context) {
  Future.delayed(Duration.zero, () {
       //your code goes here.
  });

  return Scaffold(
     
  );
} 

Reference:

https://www.fluttercampus.com/guide/230/setstate-or-markneedsbuild-called-during-build/