Reset MultiSelect in flutter - flutter

Question

I have 2 multiselect, when i select the item in one of them it has to show the selected items in a listview, but when i select the items in the second multiselect the event reset the first one. how can i resolve this problem?
this is the multiselect in witch one the _materialesSeleccionados variable is set, this variable is used by listview to show the information:
this is the body in my scaffold where I show the multiselects and the listview only shows when _materialesSeleccionados is not empty:
return Scaffold(
appBar: AppBar(
title: Center(child: Text("Tareas y Materiales")),
),
body:SingleChildScrollView(
child: Column(
children: [
_selectTareas(),
_selectMateriales(),
_materialesSeleccionados.isEmpty? Column() : Padding(
padding: const EdgeInsets.only(top:20, bottom: 20),
child: listaMateriales(),
),
_buttonFinalizar(context, argumentos['des_id'])
],
),
)
);
MultiSelectBottomSheetField(
initialChildSize: 0.4,
listType: MultiSelectListType.CHIP,
searchable: true,
buttonText: const Text("Seleccione los Materiales"),
title: const Text("Materiales"),
items: _itemsMateriales,
onConfirm: (values) {
setState(() {
_materialesSeleccionados = values;
});
//listaMateriales();
},
chipDisplay: MultiSelectChipDisplay(
chipColor: Colors.white,
textStyle: const TextStyle(color: Colors.black),
),
),
this is the main screen:
this is the screen after to select the item in the first multiselect:
this is the screen of the second multiselect befero to select the items:
when I select the items in the second multiselect these appear in the listview, but the selected items from the first one they desappear, can i to do?