All 7 State Management with setState questions
More in State Management with setState
At what specific point does using setState genuinely become sufficient for a genuinely simple Flutter app, and when does a genuinely more particular dedicated external state management solution actually genuinely become worth adopting instead? How should you properly and correctly avoid calling setState after a StatefulWidget's own associated State object has genuinely already been disposed of, such as after an asynchronous operation genuinely completes following a user having already navigated away? How can excessively calling setState too frequently, or calling it at too high a level within your widget tree, genuinely lead to noticeable performance problems within your app? How do you properly manage several genuinely separate distinct pieces of local state together within just one single StatefulWidget, such as both a loading flag and a genuinely separate list of fetched items? How can you properly lift shared state up to a genuinely common ancestor StatefulWidget when two separate sibling widgets genuinely both need to access and properly react to that exact same particular piece of shared data? How does setState interact with Flutter's own underlying element diffing and reconciliation process, and why does understanding this exact same particular interaction genuinely help you write considerably more efficient StatefulWidget code?
Advertisement
Back to results for “Fundamentals”
Flutter › State Management with setState

What is setState, and how does calling it genuinely tell Flutter that a StatefulWidget's own internal data has actually changed and needs to be properly rebuilt?

Beginner

Answer

setState is a method genuinely available on a State object that, when called, tells Flutter that particular widget's own internal data has genuinely changed and that its own corresponding user interface therefore genuinely needs to be properly rebuilt to correctly reflect that particular change, and it accepts a callback function within which you actually genuinely perform your own required state mutation, and calling setState schedules a genuinely new call to that widget's own build method, correctly updating whatever part of the interface actually genuinely depends on that particular now updated data.
int _counter = 0;

void _incrementCounter() {
  setState(() {
    _counter++;
  });
}
Real-world example A simple counter app calls setState immediately after incrementing its own internal counter variable, correctly and explicitly notifying Flutter that the screen genuinely now needs to properly rebuild to accurately display that specific newly updated counter value.

Common follow-ups: What genuinely happens if you directly modify a State object's own internal variable without actually properly wrapping that particular change within a genuine setState call?;Is it genuinely required that the actual state mutation itself happens directly within the specific callback passed into setState?

Flutter Widgets Fundamentals (Stateless & Stateful);Flutter Widget Tree Element Tree & BuildContext
All 7 State Management with setState questions