Flutter Error: The Method toDouble() was called on null, Tried calling toDouble

Question

I am stuck on the error saying toDouble was called on null. I have checked my code many times and I can't figure out whats happening.

This is the code for bottom_sheet_panel

import 'package:flutter/material.dart';
import 'package:freezeria/Screens/services/database.dart';
import 'package:freezeria/common_code/common.dart';
import 'package:freezeria/common_code/loader.dart';
import 'package:freezeria/req_info/shakes.dart';
import 'package:freezeria/req_info/user.dart';
import 'package:provider/provider.dart';

class bottomSheetPanel extends StatefulWidget {
  @override
  _bottomSheetPanelState createState() => _bottomSheetPanelState();
}

class _bottomSheetPanelState extends State<bottomSheetPanel> {
  final _formkey = GlobalKey<FormState>();
  final List<String> blending = ['1', '2', '3', '4', '5'];
  final List<String> cupsize = ['Select', 'Small', 'Medium', 'Large'];
  final List<String> flavour = [
    'Chocolate',
    'Vanilla',
    'Strawberry',
    'Blueberry',
    'Raspberry',
    'Kiwi',
    'Select'
  ];
  final List<String> cream = [
    'Whipped',
    'Caramel',
    'Chocolate',
    'Strawberry',
    'Select'
  ];
  final List<String> toppings = [
    'Oreo',
    'Cherry',
    'Strawberry',
    'Sweet Lime',
    'Waffle',
    'Blackberries',
    'Select'
  ];

  String _currentName;
  String _currentCupSize;
  int _currentBlend;
  String _currentFlavour;
  String _currentCream;
  String _currentToppings;
  @override
  Widget build(BuildContext context) {
    final receiveUser = Provider.of<User>(context);

    return StreamBuilder<UserData>(
        stream: Database(uid: receiveUser.uid).userDataStream,
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            UserData recentData = snapshot.data;
            return Form(
              key: _formkey,
              child: SingleChildScrollView(
                child: Column(
                  children: [
                    Text(
                      "Update Your Data",
                      style: TextStyle(fontSize: 20.0),
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    TextFormField(
                      initialValue: recentData.Name,
                      decoration:
                          decorationCode.copyWith(hintText: 'Enter your name'),
                      validator: (val) =>
                          val.isEmpty ? 'Please enter a name' : null,
                      onChanged: (val) => setState(() {
                        return _currentName = val;
                      }),
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    DropdownButtonFormField(
                      value: _currentCupSize ?? recentData.CupSize,
                      items: cupsize.map((size) {
                        return DropdownMenuItem(
                          value: size,
                          child: Text('$size Size'),
                        );
                      }).toList(),
                      onChanged: (val) => setState(() {
                        return _currentCupSize = val;
                      }),
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    Slider(
                      value: (_currentBlend ?? recentData.Blend).toDouble(),
                      activeColor:
                          Colors.grey[_currentBlend ?? recentData.Blend],
                      inactiveColor:
                          Colors.grey[_currentBlend ?? recentData.Blend],
                      min: 100.0,
                      max: 700.0,
                      divisions: 6,
                      onChangeEnd: (val) => setState(() {
                        return _currentBlend = val.round();
                      }),
                      
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    DropdownButtonFormField(
                      value: _currentFlavour ?? recentData.Flavour,
                      items: flavour.map((flav) {
                        return DropdownMenuItem(
                          value: flav,
                          child: Text('$flav Flavour'),
                        );
                      }).toList(),
                      onChanged: (val) => setState(() {
                        return _currentFlavour = val;
                      }),
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    DropdownButtonFormField(
                      value: _currentCream ?? recentData.Cream,
                      items: cream.map((crem) {
                        return DropdownMenuItem(
                          value: crem,
                          child: Text('$crem Cream'),
                        );
                      }).toList(),
                      onChanged: (val) => setState(() {
                        return _currentCream = val;
                      }),
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    DropdownButtonFormField(
                      value: _currentToppings ?? recentData.Toppings,
                      items: toppings.map((top) {
                        return DropdownMenuItem(
                          value: top,
                          child: Text('$top Toppings'),
                        );
                      }).toList(),
                      onChanged: (val) => setState(() {
                        return _currentToppings = val;
                      }),
                    ),
                    SizedBox(
                      height: 20.0,
                    ),
                    ElevatedButton(
                      onPressed: () async {
                        print(_currentName);
                        print(_currentBlend);
                        print(_currentCupSize);
                        print(_currentFlavour);
                        print(_currentToppings);
                      },
                      style: ButtonStyle(
                        backgroundColor: MaterialStateProperty.all<Color>(
                            Colors.purple[300]),
                        foregroundColor:
                            MaterialStateProperty.all<Color>(Colors.white),
                      ),
                      child: Text(
                        'UPDATE',
                        style: TextStyle(color: Colors.white),
                      ),
                    )
                  ],
                ),
              ),
            );
          } else {
            Loading();
          }
        });
  }
}

The toDouble() in Slider Function is giving error, also recentData.name is not updating the name in the bottom sheet.

It is seen that _currentBlend and recentData are giving null values, how do I correct it?

Any help will be much appreciated:)

Answer 1

you would use constant value if there have any possibility.

Like:

value: (_currentBlend ?? 0).toDouble(),