Why does Flutter favor composition over inheritance for building widgets?
Short Answer
Flutter widgets are meant to be combined (composed) into new widgets rather than extended via subclassing, because composition keeps widgets small, reusable, and independently testable — Flutter's own framework widgets are built this way.
You could subclass ElevatedButton and override its build method, but Flutter's own widgets are deliberately shallow and specific — a Container, for example, is itself just composed internally of Padding, DecoratedBox, and other primitives. The idiomatic pattern for a 'custom button with extra behavior' is to wrap or combine existing widgets into a new one, not extend a concrete widget class.
This matters practically: composed widgets can mix and match capabilities freely, while inheritance would force a rigid single-parent hierarchy. It also plays well with Flutter's rebuild model — small, focused widgets rebuild cheaply and independently.
Common Mistakes
- ×Subclassing StatelessWidget/StatefulWidget solely to extend framework widget behavior, when composing a new widget from existing ones would be idiomatic.
- ×Building a single giant widget class instead of splitting it into smaller composed pieces.
Interview Tips
- →Reference that Container itself is a composed widget internally — a concrete example that shows real understanding, not just theory.