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Description:

after layout

Flutter After Layout #

Brings functionality to execute code after the first layout of a widget has been performed, i.e. after the first frame has been displayed.
Quick Usage #
Add with AfterLayoutMixin<MyWidget> mixin to your State<MyWidget> class and then implement the FutureOr<void> afterFirstLayout(BuildContext context) abstract method. Code in this method will be called the first time this widget is laid out on the screen.
Motivation #
If you want to display a widget that depends on the layout, such as a Dialog or BottomSheet, you can not use that widget in initState.
You might have tried this.
BAD CODE
import 'package:flutter/material.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> {
@override
void initState() {
super.initState();
// NOTE: Calling this function here would crash the app.
showHelloWorld();
}

@override
Widget build(BuildContext context) {
return Scaffold(
body: Container(color: Colors.red),
);
}

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'),
)
],
);
},
);
}
}
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Usage #
This demo showcases how this package resolves the shortcomings shown above:
GOOD CODE
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'),
)
],
);
},
);
}
}
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