Problem Statement
What happens when you call setState() in a StatefulWidget?
Explanation
SetState() marks the State object as dirty, telling Flutter's framework that the internal state has changed and the widget tree needs to be rebuilt. Flutter schedules a rebuild, calling build() again during the next frame to create a new widget tree with the updated state. The actual rebuild happens asynchronously, not immediately when setState() is called.
You should only call setState() when you've changed state variables that affect what build() returns. Calling setState() without actually changing anything still triggers a rebuild, wasting resources. Always update state inside the setState() callback function to ensure Flutter knows about the change.
SetState() should only be called from the UI thread and never from callbacks that might run after the widget is disposed. Check the mounted property before calling setState() in async callbacks to avoid errors when the widget has been removed from the tree. Never perform expensive operations inside setState() - only update state variables, then let build() handle the UI update.
