Flutter formkey exception displayed _CastError (Null check operator used on a null value)

Question

I have created a form by wrapping a column widget in Form() as so

Form(
      key: formKey,
      child: Column(
        children: [

But when I try to set final isValid = formKey.currentState!.validate(); to check, I get an exception has occured message _CastError (Null check operator used on a null value) Any advice? Example Pic

Answer 1

Thanks in part to Void Void the solution is instead of declaring a variable isVaild. Check formKey.currentState!.validate() on press for the button as so

onPressed: () {
                  if (!formKey.currentState!.validate()) return;
                  AccountUpdate.updatePassword(
                      _confirmController.text, context);
                },

Answer 2

At that point the currentState is null, you are attempting to validate the form before it's built. It would make more sense to validate the form in a callback when some submit button is clicked, etc. Check Link to flutter docs for an example.

Answer 3

you need to create function like this and call when some submit button is clicked, etc. Thanks.

void _saveForm() {
final isValid = formKey.currentState!.validate();
if (!isValid) {
  // ignore: avoid_returning_null_for_void
  return null;
}
_form.currentState!.save(); 
 // .... extra code
}