Managing UI Updates with setState

Flutter apps are built from widgets, and many of these widgets need to change over time in response to user interactions or data updates. To handle these dynamic changes, Flutter provides stateful widgets. A stateful widget has a mutable state object that can update its appearance or behavior. The setState method is central to this process: it tells Flutter that the widget's state has changed and the UI should be rebuilt to reflect those changes.

When you call setState inside a stateful widget, Flutter marks that widget as "dirty" and schedules a rebuild. This means the build method runs again, updating the UI to show the latest state values. In the counter example, pressing the button calls _incrementCounter, which uses setState to increase _count. Flutter then rebuilds the widget, and you see the new count on screen.