after_layout 1.1.1

Execute code after the first layout of your widget has been performed, i.e. after the first frame has been displayed.

example/example.dart

import 'package:flutter/material.dart';
import 'package:after_layout/after_layout.dart';

void main() => runApp(const MyApp());

@immutable
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: 'After Layout - Good Example',
      home: HomeScreen(),
    );
  }
}

@immutable
class HomeScreen extends StatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  HomeScreenState createState() => HomeScreenState();
}

class HomeScreenState extends State<HomeScreen> with AfterLayoutMixin<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(color: Colors.red),
    );
  }

  @override
  void afterFirstLayout(BuildContext context) {
    // Calling the same function "after layout" to resolve the issue.
    showHelloWorld();
  }

  void showHelloWorld() {
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          content: const Text('Hello World'),
          actions: <Widget>[
            TextButton(
              onPressed: () => Navigator.of(context).pop(),
              child: const Text('DISMISS'),
            )
          ],
        );
      },
    );
  }
}