Error displaying SnackBar or AlertDialog when returning from another screen

I have an interface with a ListView, each element has a PopupMenuButtonwith an option, this option sends information to another screen

layout of the widget where thePopupMenuButton

class _PruebaPantallaState extends State<PruebaPantalla> {
  int count = 0;
  @override
  Widget build(BuildContext context) {
    print("6.-Pantalla prueba");
    // TODO: implement build
    return Scaffold(
      body: getApidataList(),
    );
  }
  FutureBuilder getApidataList() {
    return FutureBuilder(
      future: ApiService.getdataList(),
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.done) {
          print("3.-Entrada (conexion establecida)");
          final data = snapshot.data;
          return ListView.separated(
            separatorBuilder: (context, index) {
              return Divider(
                height: 2,
                color: Colors.black,
              );
            },
            itemBuilder: (context, index) {
              return ListTile(
                title: Text(
                  data[index]['dataTitulo'].toString(),
                  style: TextStyle(
                      color: Colors.black, fontWeight: FontWeight.bold),
                ),
                subtitle: Text(data[index]['dataTextoBiblico'].toString()),
                onTap: () {
                  datadb datadb =
                      datadb("", 0, 0, "", "", "", "", "", "", "", 0);
                  datadb.setdataId = data[index]["dataId"];
                  datadb.setdataTipo = data[index]["dataTipo"];
                  datadb.setdataNum = data[index]["dataNum"];
                  datadb.setdataNumMasc = data[index]["dataNumMasc"];
                  datadb.setdataTitulo = data[index]["dataTitulo"];
                  datadb.setdataContenido = data[index]["dataContenido"];
                  datadb.setdataPartitura = data[index]["dataPartitura"];
                  datadb.setdataTextPublic =
                      data[index]["dataTextoBiblico"];
                  datadb.setdataDatosPublic =
                      data[index]["dataDatosComplementarios"];
                  datadb.setdataNota = data[index]["dataNota"];
                  datadb.setdataFechaActualizacion =
                      data[index]["dataFechaActualizacion"];
                  datadb.setdataStatus = 1;
                  navigateToDetail(datadb);
                },
                trailing: PopupMenuButton<dynamic>(
                    onSelected: showMenuSelection,
                    itemBuilder: (context) => [
                          PopupMenuItem(
                            child: Text("Agregar a mis listas"),
                            value: data[index],
                          )
                        ]),
              );
            },
            itemCount: data.length,
          );
        }
        return Center(
          child: CircularProgressIndicator(),
        );
      },
    );
  }


  void navigateToDetail(datadb data) async {
    bool result =
        await Navigator.push(context, MaterialPageRoute(builder: (context) {
      return dataDetalle(todo: data);
    }));
  }


  void showMenuSelection(dynamic value) async {
    bool result = await Navigator.push(
      context,
      MaterialPageRoute(
        builder: (context) => Play_List(value),
      ),
    );
    if (result) {
      print('>>>>>>>>>>>>>>Mostrando SnackBar<<<<<<<<<<<<');
      final snackBar = SnackBar(
        content: Text('Se agrego correctamente a la lista'),
      );
      Scaffold.of(context).showSnackBar(snackBar);
      print(
          "Se agrego correctamente a la lista--------------------------------");
    }
  }

  void updateListView() {
    final Future<Database> dbFuture = databaseHelper.initializeDatabase();
    dbFuture.then((databse) {
      Future<List<datadb>> dataListFuture = databaseHelper.getdataList();
      dataListFuture.then((dataList) {
        setState(() {
          this.dataList = dataList;
          this.count = dataList.length;
        });
      });
    });
  }
}

This part is where you are redirected to another screen

trailing: PopupMenuButton<dynamic>(
    onSelected: showMenuSelection,
    itemBuilder: (context) => [
          PopupMenuItem(
             child: Text("Agregar a mis listas"),
             value: data[index],
          )
    ]),

MethodshowMenuSelection Which is supposed to receive a type value on return boolto display aSnackBar

void showMenuSelection(dynamic value) async {
    bool result = await Navigator.push(
      context,
      MaterialPageRoute(
        builder: (context) => Play_List(value),
      ),
    );
    if (result) {
        final snackBar = SnackBar(
            content: Text('Se agrego correctamente a la lista'),
        );
        setState(() {
            Scaffold.of(context).showSnackBar(snackBar);
        });
    }
}

If I remove the setStateit sends me the following exception in the same way I try to use a showDialogand it sends the same exception

_AssertionError ('package:flutter/src/material/scaffold.dart': Failed assertion: line 1184 pos 12: 'context != null': is not true.)

If I put the setStateit sends me the following exception

FlutterError (setState() called after dispose(): _PruebaPantallaState#d31fe(lifecycle state: defunct, not mounted) This error happens if you call setState() on a State object for a widget that no longer appears in the widget tree (eg, whose parent widget no longer includes the widget in its build).This error can occur when code calls setState() from a timer or an animation callback.The preferred solution is to cancel the timer or stop listening to the animation in the dispose() callback.Another solution is to check the "mounted" property of this object before calling setState() to ensure the object is still in the tree.This error might indicate a memory leak if setState() is being called because another object is retaining a reference to this State object after it has been removed from the tree.To avoid memory leaks, consider breaking the reference to this object during dispose().)

To return after adding to the other interface I use the following method The method contains much more information but I don't think it is necessary to include it since the one that returns to the interface is only one line. In case all the information is required, I can add it.

void navigateToDetail(dynamic lista, BuildContext newContext) async {
    Navigator.pop(context,true);
}