use<Result, Data> function

Result use<Result, Data>(GetHook<Result, Data> getHook, { required Object? key, required Data data, required String debugLabel, })

Registers a Hook and returns its value.

Must be called from within a HookWidget.build method. See Hook for more explanation.

Implementation

Result use<Result, Data>(
  GetHook<Result, Data> getHook, {
  required Object? key,
  required Data data,
  required String debugLabel,
}) {
  final HookElement? currentElement = HookElement._current;
  if (currentElement == null) {
    assert(
      throw FlutterError.fromParts([
        ErrorSummary(
          'Attempted to access $debugLabel '
          "outside of a hook widget's build method.",
        ),
      ]),
    );
    return getHook().build();
  }
  final _HookEntry? currentEntry = currentElement._currentEntry;

  Hook<Result, Data> init() {
    assert(Hook._debugInitializing = true);
    final Hook<Result, Data> hook =
        getHook()
          .._key = key
          .._data = data
          .._element = currentElement
          .._debugLabel = debugLabel
          ..initHook();
    assert(!(Hook._debugInitializing = false));

    return hook;
  }

  final _HookEntry entry;
  late final Object? oldData = currentEntry?.value._data;

  if (currentEntry case _HookEntry(value: final hook) when oldData is Data) {
    entry = currentEntry;
    if (key != hook._key) {
      (currentElement._needDispose ??= LinkedList()).add(_HookEntry(hook));
      entry.value = init();
    } else if (data != oldData) {
      entry.value
        .._data = data
        ..didUpdate(oldData);
    }
  } else {
    if (currentEntry != null) {
      currentElement._unmountAllRemainingHooks();
      if (!currentElement._debugDidReassemble) {
        throw StateError(
          'Type mismatch between hooks:\n'
          '  - old hook: ${currentEntry.value.runtimeType}\n'
          '  - current hook: $debugLabel',
        );
      }
    }
    entry = _HookEntry(init());
    currentElement
      .._currentEntry = entry
      .._hooks.add(entry);
  }

  final Result result = entry.value.build() as Result;
  assert(() {
    entry.value._debugPreviousResult = result;
    return true;
  }());
  currentElement._currentEntry = entry.next;
  return result;
}