Non-nullable instance field '_selectedDate' must be initialized

Question

I am developing an Expenses Management App in flutter, Here I am trying to create a DateTimePicker using showDatePicker(). therefore Inside my presentDateTimePicker() function i am calling showDatePicker() method.

and I am creating a variable for selectedDate where I am not initializing it to a current value since it will change based on the user input.

Inside my setState() method I use _selectedDate = pickedDate.

Still, it shows an error saying "non-nullable instance field"

My widget

//flutter imports
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';
import 'package:intl/intl.dart';

class NewTransaction extends StatefulWidget {
  final Function addTx;

  NewTransaction(this.addTx);

  @override
  _NewTransactionState createState() => _NewTransactionState();
}

class _NewTransactionState extends State<NewTransaction> {
  final _titleController = TextEditingController();
  final _amountController = TextEditingController();
  final _brandNameControlller = TextEditingController();
  DateTime _selectedDate;

  void _submitData() {
    final enteredTitle = _titleController.text;
    final enteredAmount = double.parse(_amountController.text);
    final enteredBrandName = _brandNameControlller.text;

    if (enteredTitle.isEmpty || enteredAmount <= 0) {
      return;
    }

    widget.addTx(
      enteredTitle,
      enteredAmount,
      enteredBrandName,
    );
    Navigator.of(context).pop();
  }

  void _presentDateTimePicker() {
    showDatePicker(
      context: context,
      initialDate: DateTime.now(),
      firstDate: DateTime(2019),
      lastDate: DateTime.now(),
    ).then((pickedDate) {
      if (pickedDate == null) {
        return;
      }
      setState(() {
        _selectedDate = pickedDate;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Card(
      elevation: 5,
      child: Container(
        padding: EdgeInsets.all(10),
        child: Column(
          children: <Widget>[
            TextField(
              autocorrect: true,
              decoration: InputDecoration(labelText: 'Title'),
              controller: _titleController,
              onSubmitted: (_) => _submitData,
              //onChanged: (val) {
              //titleInput = val;
              //},
            ),
            TextField(
              autocorrect: true,
              decoration: InputDecoration(labelText: 'Amount'),
              controller: _amountController,
              keyboardType: TextInputType.number,
              onSubmitted: (_) => _submitData,
              //onChanged: (val) => amountInput = val,
            ),
            TextField(
              autocorrect: true,
              decoration: InputDecoration(labelText: 'Brand Name'),
              controller: _brandNameControlller,
              onSubmitted: (_) => _submitData,
              //onChanged: (val) => brandInput = val,
            ),
            Container(
              height: 70,
              child: Row(
                children: <Widget>[
                  Text(_selectedDate == null
                      ? 'No Date Chosen'
                      : 'Picked Date: ${DateFormat.yMd().format(_selectedDate)}'),
                  FlatButton(
                    onPressed: _presentDateTimePicker,
                    child: Text(
                      'Chose Date',
                      style: TextStyle(fontWeight: FontWeight.bold),
                    ),
                    textColor: Theme.of(context).primaryColor,
                  ),
                ],
              ),
            ),
            RaisedButton(
              onPressed: _submitData,
              child: Text('Add Transaction'),
              color: Theme.of(context).primaryColor,
              textColor: Theme.of(context).textTheme.button!.color,
            ),
          ],
        ),
      ),
    );
  }
}

Solution

If the value is nullable just mark the variable as such DateTime? _selectedDate;

And whenever you would use it just check for null first:

Text(_selectedDate == null
? 'No Date Chosen'
: 'Picked Date: ${DateFormat.yMd().format(_selectedDate!)}'),
// Here you do know that the value can't be null so you assert to the compiler that

Check out the official docs on null safety they are extremely high quality and instructive. There you can read about when to use nullable ? non nullable or late variables.

Comments

[hamjeth Misree]

Thank you so much. Pretty much appreciated