Building interfaces.
WHAT A WIDGET IS
An immutable description of part of the interface.
WHAT THE TWO KINDS ARE
Stateless, depending only on its configuration Stateful, holding state that changes over time
WHAT HAPPENS ON A STATE CHANGE
The build method runs again, producing a new description.
WHAT THE FRAMEWORK DOES
Compares descriptions and updates only what changed.
WHAT COMPOSITION MEANS HERE
Behaviour added by wrapping, rather than by configuring one widget with many options.
WHAT THAT PRODUCES
Deeply nested widget trees, which surprise newcomers.
WHAT TO DO ABOUT DEPTH
Extract widgets into named classes.
WHY CLASSES RATHER THAN METHODS
The framework can then skip rebuilding them when nothing changed.
WHAT KEYS DO
Preserve identity when widgets move or reorder.
WHEN THEY MATTER
Lists that reorder, and widgets holding state.
WHAT TO USE FOR LONG LISTS
The builder variants, creating only visible items.
WHAT TO AVOID
Very large build methods Heavy computation in build Rebuilding large subtrees for a small change
