StatefulWidget in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a StatefulWidget in Flutter?

A StatefulWidget is a widget that can change its appearance over time because it holds some state information that can be updated.

beginner

What method do you override to create the mutable state for a StatefulWidget?

You override the <code>createState()</code> method to return an instance of a State subclass that holds the widget's mutable state.

beginner

How do you update the UI when the state changes in a StatefulWidget?

You call <code>setState(() { ... })</code> inside the State class to tell Flutter to rebuild the widget with the new state.

intermediate

Why should you avoid putting mutable state inside the StatefulWidget class itself?

Because the StatefulWidget is immutable; the mutable state belongs in the separate State class to keep UI and state logic separate.

intermediate

What lifecycle method is called when a StatefulWidget is first inserted into the widget tree?

The initState() method is called once when the State object is created and inserted into the tree.

Which method must you override to create the state for a StatefulWidget?

A dispose()

B build()

C initState()

D createState()

The createState() method returns the State object that holds the mutable state for the StatefulWidget.

What does calling setState() inside a State class do?

A Rebuilds the widget with updated state

B Pauses the app

C Creates a new StatefulWidget

D Deletes the widget

setState() tells Flutter to rebuild the widget so the UI reflects the updated state.

Where should you store mutable state in a StatefulWidget?

A Inside the StatefulWidget class

B In a separate StatelessWidget

C Inside the State class

D In the main() function

Mutable state belongs in the State class, not the StatefulWidget class, which is immutable.

Which lifecycle method is called only once when the State object is created?

A initState()

B dispose()

C build()

D didUpdateWidget()

initState() is called once when the State object is first created.

What happens if you forget to call setState() after changing state variables?

A The app will crash

B The UI will not update

C The widget will rebuild automatically

D The state will reset

Without setState(), Flutter does not know to rebuild the widget, so the UI stays the same.

Explain how StatefulWidget and its State class work together to manage changing UI.

Think about how a widget can change on screen when you press a button.

Describe the purpose of the initState() method in the lifecycle of a StatefulWidget.

When you first open an app screen, what setup might you need?