Programmatically open dropdown

show_dropdown.dart

var items = ["Howdy", "Hello", "Hi", "Salud"];
void _showDropdownMenu(BuildContext context) {
  final RenderBox button = context.findRenderObject() as RenderBox;
  final RenderBox overlay =
      Overlay.of(context)!.context.findRenderObject() as RenderBox;
  final RelativeRect position = RelativeRect.fromRect(
    Rect.fromPoints(
      button.localToGlobal(Offset.zero, ancestor: overlay),
      button.localToGlobal(button.size.bottomLeft(Offset.zero),
          ancestor: overlay),
    ),
    Offset.zero & overlay.size,
  );

  showMenu<String>(
    context: context,
    position: position,
    items: items.map((String item) {
      return PopupMenuItem<String>(
        value: item,
        child: Text(item),
      );
    }).toList(),
  ).then((String? newValue) {
    if (newValue != null) {
      // setState(() {
      //   selectedItem = newValue;
      // });
    }
  });
}