Flutter Widget Architect

Structure Flutter widget trees and state so rebuilds start and stop where you intend and build() is a pure, cheap function of state.

Workflow

1. Decompose into widget classes, not methods. Split a deep build() into small StatelessWidget/StatefulWidget subclasses. Never extract subtrees into _buildX() helper methods — a helper always re-runs with its enclosing build(), while a separate const widget is skipped when its inputs are unchanged. Mark const everywhere the analyzer allows.
2. Keep build() pure. build() must read state and return widgets only — no network calls, timers, setState, or controller allocation. Create AnimationController, TextEditingController, StreamSubscription, etc. in initState or a provider, and dispose every one in dispose.
3. Pick one state tool and scope it. Use Riverpod for dependency-injected, testable state with autoDispose for screen-scoped data; use Bloc for explicit event-to-state transitions over an auditable stream. Do not mix both in one feature. For purely local ephemeral UI state (a toggle, a single text field), use StatefulWidget + setState — do not reach for a global store.
4. Watch the narrowest unit. Subscribe to one field with ref.watch(provider.select(...)) or a Bloc buildWhen, never the whole model. Use ref.read for one-shot actions inside callbacks, never to react to changes.
5. Stop rebuilds at the boundary. Wrap only the changing subtree in Consumer/BlocBuilder/ValueListenableBuilder and leave the static shell (AppBar, background) outside it. Pass child through builders to reuse subtrees the rebuild does not touch.
6. Build lists lazily with stable keys. Use ListView.builder/SliverList so off-screen items are not built. Give items a ValueKey on the model id so element and state survive reorder.
7. Bound your layout. Wrap flexible children in Expanded/Flexible inside Column/Row to prevent unbounded-height constraints, overflow, and layout thrash.

Quality bar

• The static shell does not rebuild when a single value changes (verify with debugPrintRebuildDirtyWidgets or DevTools rebuild tracking).
• Every controller, subscription, and AnimationController created is disposed; flutter analyze reports no dispose or prefer_const_constructors warnings.
• Long or unbounded lists use a lazy builder, never a mapped Column/ListView(children: [...]).
• State scope matches sharing: local state stays in StatefulWidget; shared/async/tested state lives in a provider or Bloc.

Do NOT

• Do NOT extract subtrees into _buildX() helper methods that return Widget.
• Do NOT do work in build() (I/O, timers, allocation, setState).
• Do NOT ref.watch a whole model when you depend on one field; use .select/buildWhen.
• Do NOT call setState on a large State to update one value; isolate it with ValueListenableBuilder or a scoped provider.
• Do NOT leave a ListView/Column building every item or with unbounded height.
• Do NOT introduce Riverpod and Bloc into the same feature.