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

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

CodePudding user response：

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.

CodePudding user response：

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
}