I have a registration Form with a Validator binded to some TextFields and Pickers, and binded to a submit Button.
One of these TextField is for email. Suppose that I have a Rest API to know if a given email is already registered or not.
Currently the Validator only checks if the given email is a valid email. I also want to check if it’s already registered: if yes, the validation must fails, the submit button must be disabled and an informative Label must be shown under the TextField in issue (the emblem icon doesn’t make sense in this case). It’s not an InputComponent, it’s a standard simple TextField.
I don’t know how to achieve this. Thank you for your support.
Showing something under the label is easy just add an error label below in the layout. If the label is blank it won't show and won't take up space.
The validation code is designed for fast client side validation. What you're talking about is server side validation and that's a result of a server error. You need to do that separately anyway by making a request and failing.
The submit button can be enabled in such a case since you don't necessarily want to delay submit but if the submit is pressed before the email check is done you can wait for that request to complete.
If you want this to go through the validator pattern you can just create a validator that returns false at first (but disable the error indications) then in the error below the validator you can write "checking email availability".
Once a result is received you just update the validator value and trigger a re-validation of the input. You can just invoke setText() again with the same text which should trigger validation.
Notice that if your making a webservice request on every data change event this will produce a pretty awful UI experience. You need to use a timer to send a delayed request when typing is done. I think I posted something like this in the past around here.