Flutter errorFlutter: “setState() or markNeedsBuild() called during build”

Why the state change is rejected, and the fix

1. 01

   setState is called inside build

   “The build method in your Flutter code isn't a good place to call setState, either directly or indirectly.” Flutter, Common Flutter errors

   build can run many times a second, for example during an animation. Changing state there asks Flutter to rebuild while it is already building. Calculate values in build without saving them, or change state in an event handler or lifecycle method.

2. 02

   A dialog or navigation is triggered from build

   “The build method isn't the right place to call showDialog because build can be called by the framework for every frame, for example, during an animation.” Flutter, Common Flutter errors

   showDialog, Navigator.push and snackbars change the widget tree, so calling them from build hits the same error even without a visible setState. Trigger them from the button that opens the screen, or after the first frame.

   // in a StatefulWidget's State
   @override
   void initState() {
     super.initState();
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (!mounted) return;
       showDialog<void>(
         context: context,
         builder: (_) => const AlertDialog(title: Text('Welcome')),
       );
     });
   }

3. 03

   Open the dialog as a route instead

   “One way to avoid this error is to use the Navigator API to trigger the dialog as a route.” Flutter, Common Flutter errors

   When a screen should open with a dialog on top, push both from the button that opens it: first the screen, then the dialog as its own route. Flutter’s docs show this pattern with Navigator and PageRouteBuilder.

4. 04

   A ChangeNotifier notifies during build

   With Provider and a ChangeNotifier, the same error appears when build calls a method that changes the model and calls notifyListeners, such as starting a data load. Start the load in initState (after the first frame if it notifies right away) or in the model itself, and only read state in build.

Checked against the vendor’s docs on November 7, 2026: Flutter docs: Common Flutter errors (setState called during build).

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