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Flutter Null check operator not working well

I’m trying to call a widget when a form is validated. However, I’m running in a bit of problem here

In my code

  final GlobalKey<FormState> formkey = GlobalKey<FormState>();

Then later

formkey.currentState!.validate() 
                      ? const SizedBox()///this is not the actual widget but just an example to simplify things
                      : Container()

Whenever I bring the ! as in formkey.currentState!.validate() and run the app, I get an error on my phone that Null check operator used on a null value. When I remove it and put ? as in formkey.currentState?.validate() I get an error in the code with the message

A nullable expression can’t be used as a condition.
Try checking that the value isn’t ‘null’ before using it as a condition

What should I do?

By the way, this is after I’ve used the validation logic in a TextFormField wrapped in a Form widget.

Tags:

2

Answers


  1. 0

    just add null aware (??) condition to handle the case when formKey is null.

    (formkey.currentState?.validate() ?? false)
                      ? const SizedBox()
                      : Container()

    Full Example Code:

    class TestCase extends StatefulWidget {
  const TestCase({super.key});

  @override
  State<TestCase> createState() => _TestCaseState();
}

class _TestCaseState extends State<TestCase> {
  final formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Form(
        key: formKey,
        child: Column(
          children: [
            (formKey.currentState?.validate() ?? false)
                ? const Text("Valid")
                : const Text("Invalid"),
            TextFormField(
              validator: (value) {
                if (value == null || value.isEmpty) {
                  return 'Please enter some text';
                }

                return null;
              },
            ),
            MaterialButton(
              onPressed: () {
                setState(() {});
              },
              child: const Text("Submit"),
            )
          ],
        ),
      ),
    );
  }
}
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  2. 0

    Add the key to the scaffold?

    Widget build(BuildContext context) {
    return Scaffold(
        key: formkey,
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