add-user-main.dart

void addUser() {
    int index = listData.length;
        listData.add(
        UserModel(
        firstName: "Norbert",
        lastName: "Kozsir",
        profileImageUrl:
            "https://pbs.twimg.com/profile_images/970033173013958656/Oz3SLVat_400x400.jpg",
        ),
    );
    _listKey.currentState
        .insertItem(index, duration: Duration(milliseconds: 500));
}