juniorFlutter
Explain the build() method.
Updated Apr 28, 2026
Short answer
The build() method describes the part of the user interface represented by the widget.
Deep explanation
Flutter framework calls the build() method in several scenarios: initially when inserting the widget into the tree, when setState is called, or when an InheritedWidget it depends on changes. It must be pure (without side effects) and return a Widget tree.
Real-world example
Constructing the visual representation of a custom button every time the button needs to render.
Common mistakes
- Making network calls or heavy computations directly inside the `build()` method, which freezes the UI.
Follow-up questions
- What is the BuildContext?
- How often can build() be called?