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Hi so I have been getting this error - "The non-nullable local variable 'newTaskTitle' must be assigned before it can be used. (Documentation) Try giving it an initializer expression, or ensure that it's assigned on every execution path." while building my flutter app. I am learning from Angela Yu's udemy course.

class AddTaskScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    late String newTaskTitle;
    return Container(
      color: const Color(0xff757575),
      child: Container(
        padding: const EdgeInsets.all(25),
        decoration: const BoxDecoration(
          color: Colors.white,
          borderRadius: BorderRadius.only(
            topLeft: Radius.circular(20),
            topRight: Radius.circular(20),
          ),
        ),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            const Text(
              'Add task',
              textAlign: TextAlign.center,
              style: TextStyle(color: Colors.lightBlueAccent, fontSize: 30.0),
            ),
            TextField(
              autofocus: true,
              textAlign: TextAlign.center,
              onChanged: (newText) {
                newTaskTitle = newText;
              },
            ),
            const SizedBox(height: 20),
            TextButton(
              child: const Text(
                'Add',
                style: TextStyle(color: Colors.white),
              ),
              style: TextButton.styleFrom(
                backgroundColor: Colors.lightBlueAccent,
              ),
              onPressed: () {
                print(newTaskTitle);
              },
            ),
          ],
        ),
      ),
    );
  }
}

If I set the String newTaskTitle as - late String newTaskTitle

late String newTaskTitle;

The following error is shown when I print the 'newTaskTitle' variable- "======== Exception caught by gesture =============================================================== The following LateError was thrown while handling a gesture: LateInitializationError: Local 'newTaskTitle' has not been initialized."

This is my first post on stackoverflow so thanks for your help!

Kaustubh Ghude
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1 Answers1

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The error is telling you exactly what the problem is. You are saying that you will be initializing the value of newTaskTitle at a 'later' time, but this must be before you use it. Typically you use a late variable initialization because you need some data passed into an object or widget to initialize it with.

late String newTaskTitle;

I can see in the TextField widget that when the text changes, you assign it to the newTaskTitle.

TextField(
  ...
  onChanged: (newText) {
    newTaskTitle = newText;
  },
),

If you first change the TextField text, then press the TextButton you should not see the error.

You can also try just providing a default value when you create the vriable

String newTaskTitle = '';

I always recommend that if you are new to Dart and null-safety, complete this codelab which will save you many headaches: https://dart.dev/codelabs/null-safety

Tom Sitter
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  • Thanks for your quick response. I tried your solution but it gives the following error - "warning: The left operand can't be null, so the right operand is never executed" – Kaustubh Ghude Apr 22 '22 at 05:18
  • Oh that's right. Typically you are initializing a `late` variable shortly after declaring it, like in a constructor. For the sake of this example problem you can change the declaration of your variable to give it a default value at initialization `String newTaskTitle = 'Not initialized'`. I'm sure Angela will do something more sensible shortly. Alternatively you can revert back to how it was and just make sure you edit the TextField before clicking the button. – Tom Sitter Apr 22 '22 at 15:50
  • Got it. Thanks for your help, Tom! – Kaustubh Ghude Apr 22 '22 at 18:39