 or markneedsbuild() called during build. flutter getx.jpg)
When working with Flutter and the GetX state management package, one common error developers encounter is:
FlutterError (setState() or markNeedsBuild() called during build. This Obx widget cannot be marked as needing to build because the framework is already in the process of building widgets.
This error occurs when setState() or markNeedsBuild() is called while the widget tree is still being constructed. Unfortunately, there's not much documentation available online regarding this issue.
In this blog, we will explain the error, discuss common causes, provide solutions, and share best practices to prevent this issue.
Understanding the Error
Why this error occurred?
This error occurs because you're trying to update an Obx(Observable) i.e (Rx variable inside an Obx widget) while Flutter is still building widget tree.
Why Does It Happen?
Flutter requires that UI updates occur after the widget tree has finished building. If you modify an observable state (inside an Obx widget) during the build process, the framework gets confused, leading to this error.
Common Causes of the Error
- Modifying Observables in the initState() Method
@override
void initState() {
super.initState();
controller.count.value = 5; // ❌ Updating an observable in initState()
}
- Updating Observables Inside the build() Method
Widget build(BuildContext context) {
controller.count.value += 1; // ❌ Modifying state during build
return Obx(() => Text('${controller.count.value}'));
}- Calling a Function That Updates State During Build
Widget build(BuildContext context) {
fetchData(); // ❌ Calling a function that updates state
return Obx(() => Text('${controller.data.value}'));
}Code breaking Alert? Let's turn those red errors into green checks!
How to Fix the Error
- Use WidgetsBinding.instance.addPostFrameCallback()
This delays the state update until after the build process completes.
@override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((_) {
controller.count.value = 5; // ✅ Safe to update after build
});
}
- Use a Future.delayed() to Defer the Update
This ensures that the observable state update happens after the build phase.
Widget build(BuildContext context) {
Future.delayed(Duration.zero, () {
if (!controller.count.isClosed) {
controller.count.value += 1; // ✅ Updating safely
}
});
return Obx(() => Text('${controller.count.value}'));
}
- Move Logic to onInit() Instead of initState()
GetX provides onInit() in controllers, which is the preferred way to initialize values.
class MyController extends GetxController {
var count = 0.obs;
@override
void onInit() {
super.onInit();
count.value = 5; // ✅ Safe initialization
}
}
Error-Proof Your Code: Best Practices You Need
- Never update observables directly in initState() or build()
- Use onInit() inside your GetX controller for initialization
- Use WidgetsBinding.instance.addPostFrameCallback() for UI updates after build
- Wrap API calls inside Future.microtask() or Future.delayed(Duration.zero, () {})
- Ensure that the controller is still active before updating its state (!controller.isClosed)
Flutter + GetX = Magic. Avoid this error and keep the spells working!
Conclusion
That pesky 'setState() or markNeedsBuild() called during build' error happens when GetX tries to update an observable state mid-build—but don't sweat it! With the right moves (onInit(), Future.delayed(), or addPostFrameCallback), you can outsmart this glitch and keep your app running smooth as butter. Still stuck? No problem— AARK TECH HUB got your back! Keep coding, keep conquering, and turn those errors into victories. Happy coding, champion!
This blog is brought to you by AARK Technology Hub – your trusted partner for innovative tech solutions and expert guidance in Flutter development and beyond. Stay tuned for more insights and tutorials to elevate your development journey!
