📐 Flutter ReadyLayoutMixin — Execute Code After First Layout

Sometimes in Flutter, you need to perform certain actions only after the widget has been fully built and laid out — for example, to:

• Start async tasks right after the UI is ready.
• Get the size of a widget (like its height or width).
• Start animations that need to know the size of something.
• Move or control scroll position after layout.
• Automatically scroll to a widget or list item.
• Update state only after the layout is done.

Make sure a widget is actually visible on the screen.

This is where ReadyLayoutMixin comes in handy. It ensures your code runs exactly once after the first layout is complete.

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❌ Without ReadyLayoutMixin

Example

class SetStateExample extends StatefulWidget {
 @override
 State<SetStateExample> createState() => _SetStateExampleState();
}

class _SetStateExample extends State<SetStateExample> {
 String label = 'Before layout';

 @override
 void initState() {
   super.initState();
   // ❌ This will throw an error if it triggers a rebuild too early
   setState(() {
     label = 'Trying to update too soon!';
   });
 }

 @override
 Widget build(BuildContext context) => Text(label);
}

✅ With ReadyLayoutMixin

Use this approach to simplify post-layout logic without having to manage frame callbacks manually.

Example

class SetStateExample extends StatefulWidget {
 @override
 State<SetStateExample> createState() => _SetStateExampleState();
}

class _SetStateExampleState extends State<SetStateExample>
   with ReadyLayoutMixin<SetStateExample> {
 String label = 'Before layout';

 @override
 void onViewReady(BuildContext context) {
   setState(() {
     label = 'Layout is ready!';
   });
 }

 @override
 Widget build(BuildContext context) => Text(label);
}

---

---

❌ Without ReadyLayoutMixin

Example

class AsyncExample extends StatefulWidget {
 @override
 State<AsyncExample> createState() => _AsyncExampleState();
}

class _AsyncExampleState extends State<AsyncExample> {
 String label = 'Loading...';

 @override
 Future<void> initState() async{
   super.initState();
   // ❌ This will throw an error on Asynchronous operation.
   await _doAsyncWork();
 }

 Future<void> _doAsyncWork() async {
   await Future.delayed(Duration(seconds: 2));
   if (mounted) {
     setState(() {
       label = 'Data loaded after layout!';
     });
   }
 }

 @override
 Widget build(BuildContext context) => Text(label);
}

---

✅ With ReadyLayoutMixin

Use this approach to simplify post-layout logic without having to manage frame callbacks manually.

Example

class AsyncExample extends StatefulWidget {
 @override
 State<AsyncExample> createState() => _AsyncExampleState();
}

class _AsyncExampleState extends State<AsyncExample>
   with ReadyLayoutMixin<AsyncExample> {
 String label = 'Loading...';

 @override
 Future<void> onViewReady(BuildContext context) async {
   // Do your async logic here
   await Future.delayed(Duration(seconds: 2));
   setState(() {
     label = 'Data loaded after layout!';
   });
 }

 @override
 Widget build(BuildContext context) => Text(label);
}