JavaFX Form Validation

[Jonathan Giles]

Thanks all for your feedback and taking the time to have a good 
discussion on this topic. I'll go off and digest everything that was 
said and will resurface in the coming weeks with a first draft plan of 
attack for your review. I feel like I am far more informed of the needs, 
and of the opinions, of the community now. Feel free to continue to 
leave your thoughts and use cases in this thread.

However, for now, I need to return to bug fixing on JavaFX 2.2.

Thanks again,
-- Jonathan

On 11/06/2012 11:52 a.m., Jonathan Giles wrote:
> Hi all,
>
> I'm currently in the very, very early stages of developing a 
> validation API for future inclusion into JavaFX. I thought rather than 
> get too far into the research and development of a proof of concept, I 
> would see what you all think. Any feedback now would be very useful.
>
> Essentially, there are a few common styles related to form validation. 
> Some of the more likely approaches include:
>
>  * The 'JGoodies Validation framework' [1] approach, where the
>    developer provides a Validator that will then run over the form and
>    gather feedback to return to the user (for example, it would test
>    that the 'name field' is not empty, and that the email address is of
>    the correct style - if either of these rules are invalid, the
>    Validator would return ValidationMessage instances inside a
>    ValidationResult). If validation fails the user is shown the text
>    out of the ValidationMessage feedback, otherwise the form would
>    submit as per usual. This validation may happen at a number of times
>    (during form submission, when focus is lost, as a key is typed,
>    etc). The nice thing about this approach is that the Validator can
>    be a part of the domain model, the presentation model, or a separate
>    thing altogether.
>  * The JSR-303 approach which uses annotations to indicate the rules
>    applicable to each field. These annotations are on the domain model,
>    and therefore assumes that the form is directly tied to a domain
>    object (which may not always be correct). I think the JSR-303 API is
>    too complex for what is needed in JavaFX, but a similar
>    implementation could be developed with a simpler API that follows
>    this approach.
>  * For lack of a better reference point, the FXForm approach [3] which
>    encapsulates the validation inside a Form object that can be placed
>    in the scene. I know this isn't explicitly (in the case of FXForm)
>    about validation, but I think it is another approach to consider.
>
> So, what does JavaFX need out of a validation framework? It's really 
> five things (I think):
>
> 1. A way for developers to validate a form by providing some means of
>    specifying rules, as well as a way to specify when it runs, how it
>    is visually represented, etc.
> 2. A way for the validation to impact upon the visual state of the form
>    (using consistent CSS pseudoclass states / style classes, as well as
>    by showing custom overlays, error messages beside the component (or
>    grouped together at the top of the form)). There must be API to
>    specify all of this.
> 3. Convenient API to simplify the validation process [3] (e.g.
>    isEmpty(String), isAlphanumeric(String), etc, etc, etc).
> 4. An API that does not require it be integrated with UI controls.
>    Doing so would prevent 3rd party UI controls to be able to be
>    validated without also implementing the API, which may prove
>    burdensome. Instead, the validation API should be separate.
> 5. A means to integrate nicely with the bindings and properties API
>    present in JavaFX today.
>
> Of the three approaches above, my personal preference is to follow the 
> JGoodies approach as I think it is the most powerful and flexible. 
> However, nothing is set in stone and I want to learn what others think.
>
> Note that at present this research does not extend to considering 
> whether there should be API related to automatically generating a form 
> from a (JavaFX) bean (and making use of the validation API to ensure 
> the input is correct). However, I am not against discussing this topic 
> as well, as long as it too integrates nicely with the rules above, as 
> well as the validation API itself, obviously. This research may full 
> into requirement three above.
>
> [1] http://www.jgoodies.com/freeware/libraries/validation/
> [2] https://github.com/dooApp/FXForm2
> [3] 
> http://www.jarvana.com/jarvana/view/com/jgoodies/validation/2.0.1/validation-2.0.1-javadoc.jar!/com/jgoodies/validation/util/ValidationUtils.html
>
> Thanks,
> -- Jonathan
>