عدم ظهور bottomsheet في فلاتر

import 'package:flutter/material.dart';
import 'package:logindesign/modules/archivedtask.dart';
import 'package:logindesign/modules/donetask.dart';
import 'package:logindesign/modules/newtask.dart';
import 'package:sqflite/sqflite.dart';

class HomeLayot extends StatefulWidget {
  @override
  _HomeLayotState createState() => _HomeLayotState();
}


class _HomeLayotState extends State<HomeLayot> {
  int currentIndex = 0;

  @override
  void initState() {

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    List<Widget> screen = [
      NewTasks(),
      DoneTasks(),
      ArchiveTasks(),
    ];

    List<String> title = ['Tasks', 'Done Tasks', 'Archived Tasks'];
    var ScaffoldKey=GlobalKey<ScaffoldState>();
    bool isBottomSheetShown=false;
    IconData fabIcon=Icons.edit;
    return Scaffold(
      key: ScaffoldKey,
      appBar: AppBar(
        title: Text(title[currentIndex]),
      ),
      body: screen[currentIndex],
      floatingActionButton: FloatingActionButton(
        child: Icon(fabIcon),

        onPressed: () {

       if(isBottomSheetShown){
         Navigator.pop(context);
         isBottomSheetShown=false;
         setState(() {
           fabIcon=Icons.edit;
         });
       }
       else{
          ScaffoldKey.currentState?.showBottomSheet((context) {
            return Container(
              width: double.infinity,
              height: 120.0,
              color: Colors.amber,

            );
          });
          isBottomSheetShown=true;
           setState(() {

            fabIcon=Icons.add;
           });
        }},
      ),
      bottomNavigationBar: BottomNavigationBar(
        type: BottomNavigationBarType.fixed,
        //elevation:0 ,
        showSelectedLabels: false,
        //  backgroundColor: Colors.blue,
        currentIndex: currentIndex,
        onTap: (index) {
          setState(() {
            currentIndex = index;
          });
          print(index);
        },
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.menu),
            label: 'Tasks',
          ),
          BottomNavigationBarItem(
              icon: Icon(Icons.check_circle_outline), label: 'Done'),
          BottomNavigationBarItem(
              icon: Icon(Icons.archive_outlined), label: 'Archived'),
        ],
      ),
    );
  }

  

هذا الكود يجب ظهور Bottomsheet عند النقر علئ floatactionbutton ,وتتغير الأيقونة أيضًا لكنها لاتعمل ..لماذا