switchLayoutBuilderWithSwitchedFlag function

Widget switchLayoutBuilderWithSwitchedFlag(Widget? currentChild, List<Widget> previousChildren)

A switch layout builder for AnimatedSwitcher, which is almost the same as AnimatedSwitcher.defaultLayoutBuilder, but this builder wraps PreviouslySwitchedWidget with tracked key to specific widgets in Stack.

Note that you should use this layout builder when you are using any kinds of UpdatableDataView, in order to invalidate the ScrollController for switched out Scrollable and Scrollbar, and deal with The provided ScrollController is currently attached to more than one ScrollPosition kinds of exceptions.

Implementation

Widget switchLayoutBuilderWithSwitchedFlag(Widget? currentChild, List<Widget> previousChildren) {
  return Stack(
    alignment: Alignment.center,
    children: [
      // previous widgets
      for (var child in previousChildren) //
        child is! KeyedSubtree
            ? child // unreachable, child is almost a KeyedSubtree
            : KeyedSubtree(
                key: child.key,
                child: PreviouslySwitchedWidget(
                  key: child.key, // <<< must set the key to track widget correctly
                  child: child.child,
                  switched: true,
                ),
              ),

      // current widget
      if (currentChild != null)
        currentChild is! KeyedSubtree
            ? currentChild // unreachable, currentChild is almost a KeyedSubtree
            : KeyedSubtree(
                key: currentChild.key,
                child: PreviouslySwitchedWidget(
                  key: currentChild.key, // <<< must set the key to track widget correctly
                  child: currentChild.child,
                  switched: false,
                ),
              ),
    ],
  );
}