onChanged returns null while trying to assign a value from a textField flutter

Question

I am trying to assign a value which is typed in by the user from a textField, but it returns null. Note that I am using a statelessWidget Here is the variable that I am trying to assign the value:

String? newTaskTitle;

Here is my code:

class AddTaskScreen extends StatelessWidget {
  const AddTaskScreen({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    String? newTaskTitle;

    return Container(
      color: Colors.black,
      child: Container(
        padding: const EdgeInsets.all(20),
        decoration: const BoxDecoration(
          color: Color(0xff1f1f1f),
          borderRadius: BorderRadius.only(
              topLeft: Radius.circular(20), topRight: Radius.circular(20)),
        ),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            const Text(
              'Add a task',
              textAlign: TextAlign.center,
              style: TextStyle(color: Colors.white, fontSize: 20),
            ),
            TextField(
              cursorColor: Colors.white38,
              decoration: const InputDecoration(
                enabledBorder: UnderlineInputBorder(
                  borderSide: BorderSide(color: Colors.white38),
                ),
                focusedBorder: UnderlineInputBorder(
                  borderSide: BorderSide(color: Colors.white38),
                ),
              ),
              textAlign: TextAlign.center,
              autofocus: true,
              onChanged: (newText) {
                newText = newTaskTitle!;
              },
            ),
            TextButton(
              style: ButtonStyle(
                backgroundColor: MaterialStateColor.resolveWith(
                    (states) => Colors.white.withOpacity(0.9)),
                overlayColor:
                    MaterialStateColor.resolveWith((states) => Colors.white),
              ),
              onPressed: () {
                if (newTaskTitle == null) {
                  Navigator.pop(context);
                  print('null');
                } else {
                  Provider.of<TaskData>(context).addTask(newTaskTitle!);
                  Navigator.pop(context);
                }
              },
              child: const Text(
                'Add',
                style: TextStyle(
                  fontSize: 15,
                  fontWeight: FontWeight.bold,
                  color: Colors.black,
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

Turn the assignment:

newText = newTaskTitle!;

becomes to this:

newTaskTitle! = newText;