Async validation

[RodolfoSilva]

A few times after sending data to the backend, the server will respond with backend validation. How can I set an error message for for a specific field?

@danvick do you have any suggestion how can I do that?

[danvick]

As it is currently in Flutter, there's no way of passing up an error to a FormField.
I've been working on the next major version of the package with this as one of the features.

Problem is currently, I'm a bit short on time.

[RodolfoSilva]

Thanks @danvick 😄

[RodolfoSilva]

Maybe I can help you, I'm short on time too. But if I can help, tell me.

[ronaldcurtis]

@RodolfoSilva Just a heads up that I have found a work-around for async validation, inspired by this article: https://medium.com/@nocnoc/the-secret-to-async-validation-on-flutter-forms-4b273c667c03

Basically, what I did was (condensed code):

class _EmailPasswordFormState extends State<EmailPasswordForm> {
  final GlobalKey<FormBuilderState> _fbKey = GlobalKey<FormBuilderState>();
 
  // We update this boolean after our async function runs
  bool _emailHasBeenTaken = false;

  // Create this custom validator that references the above variable
  FormFieldValidator validateEmailIsUnique() {
    return (val) => _emailHasBeenTaken ? "This email has been taken" : null;
  }

// ...Skipping down to where we add validators:
validators: [
  FormBuilderValidators.required(),
  FormBuilderValidators.email(),
  // Add your validator function
  validateEmailIsUnique(),
],
        
// ...Skipping down to where we submit the form:
onPressed: () {
  // Run sync validations first. If all good, then call our async function.
  if (_fbKey.currentState.saveAndValidate()) {
    // Emulating an async call here:
    Future.delayed(Duration(seconds: 1), () {
      setState(() {
        // Pretend the response says email is not unique:
        _emailHasBeenTaken = true;
      });
      
      // Re-run the validations to show the error message
      _fbKey.currentState.saveAndValidate();
    });
  }
}

I hope that helps!

[danvick]

Maybe I can help you, I'm short on time too. But if I can help, tell me.

Hi @RodolfoSilva,
I have made some progress in the v4.0.0 milestone. I may need your help in testing it out. Thanks in advance.

[RodolfoSilva]

Ok @danvick , I'll check later :D

[danvick]

I'm marking this as a duplicate of #123.