adaptive-ui-and-lists-with-flutter-helper-utils

Adaptive UI and typed lists with flutter_helper_utils

Two surfaces where agents invent parameter names and misremember the breakpoint model. Use the exact contracts below.

Breakpoints: the matching rule is UPPER-bound

Defaults (Breakpoint.defaults): mobile width 600, tablet width 1200, desktop width 1800. Matching returns the FIRST breakpoint whose width >= available width (widths are ceilings, NOT min-widths):

• 500 wide -> mobile; exactly 600 -> mobile (inclusive)
• 601-1200 -> tablet; 1201-1800 -> desktop; beyond the last -> last

Do not assume the common min-width model (mobile 0+, tablet 600+, desktop 1200+) - boundaries land differently (600 exactly is MOBILE here). Custom sets: Breakpoint(width: 900, name: 'compact'); the provider sorts them by width. Comparisons: bp.isMobile/isTablet/isDesktop (name match), >/</isBetween(lower, upper) (width match).

Setup and reading

runApp(PlatformTypeProvider(          // safe ABOVE MaterialApp (9.0+)
  // breakpoints: Breakpoint.defaults,
  child: MyApp(),
));

final bp = context.watchBreakpoint;   // rebuilds on change (NOT context.breakpoint)
final bp2 = context.readBreakpoint;   // one-shot, no rebuild (NOT .of(listen: false))

• Missing provider throws FlutterError - there is no null fallback; wrap the app root, not a subtree, unless scoping is intentional.
• BreakpointLayoutBuilder(builder: (context, breakpoint) => ...) and PlatformInfoLayoutBuilder(builder: (context, info) => ...) are the widget forms; PlatformSizeInfo carries breakpoint, orientation, and platform (from PlatformEnv.targetPlatform).
• The provider measures the LayoutBuilder constraints first, then falls back to MediaQuery, then the physical view - so it reflects the space the provider actually occupies.

TypedListView - exact parameter names

TypedListView<Product>(
  items: products,
  itemBuilder: (context, index, item) => ProductTile(item),  // THIS order
  spacing: 12,                        // gap; do NOT also pass separatorBuilder
  emptyBuilder: (context) => const EmptyState(),   // NOT emptyWidget
  onRefresh: () => reload(),          // wraps in RefreshIndicator
  onEndReached: () => loadMore(),     // NOT onLoadMore/onPaginate
  onEndReachedThreshold: 200,         // px before the end (default 200)
  isLoadingMore: isLoading,           // gates repeat onEndReached calls
  header: const ListHeader(),         // direct widgets, not builders
  footer: const ListFooter(),
  paginationWidget: const LoadingSpinner(),  // shown before footer
  itemKeyBuilder: (item) => ValueKey(item.id), // stable keys + correct
)                                              // findChildIndexCallback

// Same surface as an extension:
products.buildListView(itemBuilder: (context, index, item) => ...);

Assert matrix (violations crash in debug):

• separatorBuilder XOR spacing - never both.
• itemExtent XOR prototypeItem - never both.
• itemExtent/prototypeItem require NO header/footer/pagination/ separators/spacing (every child must have the same extent).
• cacheExtent (deprecated 9.1) XOR scrollCacheExtent; prefer scrollCacheExtent: ScrollCacheExtent.pixels(300) or ScrollCacheExtent.viewport(1.5).

Behavior notes:

• onEndReached fires on scroll notifications whenever remaining extent <= threshold and isLoadingMore is false - keep isLoadingMore true until the fetch settles or it will re-fire.
• showScrollbar: true wraps in Scrollbar using the SAME controller you pass; provide one when you enable it.
• buildListView eagerly copies the iterable to a list.
• TypedSliverList mirrors items/itemBuilder/header/footer/separators/ spacing/itemKeyBuilder for CustomScrollView use (no physics/refresh/ scrollbar - those belong to the outer scroll view).

Scroll position helpers (ScrollController)

controller.animateToStart() / animateToEnd() / jumpToEnd(), animateBy(delta), pageScroll(...), scrollToPercentage(50), snapToIndex(i, itemExtent: 72), scrollProgress (0-1), isAtStart/isAtEnd, isNearEnd(threshold: 50), canScroll, isUserScrollingForward, debugPrintScrollInfo(). Guard multi-client controllers with hasSingleClient.

Step 0: Inspect the project first

1. Resolved version: grep -A2 'flutter_helper_utils' pubspec.lock (9.x documented here; TypedListView pre-8.5 had itemBuilder(item) and headerBuilder/footerBuilder - see the migrate skill).
2. Find existing providers: grep -rn "PlatformTypeProvider" lib/ - nesting a second provider silently re-scopes breakpoints.

Verification

• flutter analyze; assert-matrix violations only appear at RUNTIME in debug builds, so run the affected screen or a widget test.
• For breakpoint changes, add a widget test pumping two sizes across a boundary (e.g. 600 and 601) and assert which layout renders.

Failure handling

• FlutterError: ... does not contain a PlatformTypeProvider: the provider is missing or below the calling context - move it up.
• List crashes with "Provide either separatorBuilder or spacing" (or the itemExtent variants): remove one side of the XOR pair.
• onEndReached firing repeatedly: isLoadingMore is not being set.
• Theme/media-query/navigation helpers: use-flutter-helper-utils skill; color parsing: colors-with-flutter-helper-utils skill.