Framework: When I have just one field on the UI, I want to easily validate the value of the field, without having to use binder or listening to event and manually show error message

[fakeh]

Hi,
I believe this is the right place to leave V8 feedback.

Shouldn't it be possible to validate/convert values in Fields without having to bind to a bean?

I have a form with a single field. It seems weird to have to bind this one field to a bean in order to validate it.

Thanks!
Dan.

[pleku]

tldr: We could make it possible to create a Binding for a field component with validators/converters without a Binder.

This is something that was left out of 8.0, you just basically should use a ValueChangeListener and trigger your validator/converter manually, setting and clearing the error message...

            TextField tf = new TextField();
            tf.addValueChangeListener(event -> {
                if (event.getValue().isEmpty()) {
                    tf.setComponentError(new UserError("Empty value not allowed"));
                } else {
                    tf.setComponentError(null);
                    Notification.show(event.getValue());
                }
            });

You can use Binder too without a bean but it requires some boilerplate

        TextField textField = new TextField();
        Binder<String> binder = new Binder<String>();
        Binding<String, String> binding = binder.forField(textField)
                .withValidator((value, context) -> value.isEmpty()
                        ? ValidationResult.error("Empty value not allowed")
                        : ValidationResult.ok())
                .bind(string -> string, this::onValueChange);
        binder.setBean("Initial Value"); // goes to textfield directly

[fakeh]

Thanks Pleku, good ideas.

[Thibstars]

What I seem to miss in this approach is the ability to check wether a field is valid. Something like textField.isValid(); would be great. This could come in handy when you have a button you only want to enable when all fields are valid, for example.

[elmot]

@Thibstars, you can use standard Vaadin 8 validation API for that. Use Binder.Binding.validate() for that.

[Thibstars]

@elmot Thanks for the suggestion. However I do still think that produces lengthy code as well. It works for me and I do think it is better than just use valuechangelisteners.

[fgrazi]

@pleku Thank you very much, but I am unable to reproduce the snippet. In:
.bind(string -> string, this::onValueChange);
What is the value of this? The compiler complains that there is no onValueChange method. Can you please explain?

[pleku]

@fgrazi that is just an example, you should replace the this::onValueChange with whatever you want to do with the updated value from the field (after it has passed the validation).

In the example it is just something that consumes a String, which is the value type of the Binder (and TextField).

[fgrazi]

Thanks pleku, but I still don't understand. Once I have a Binder.BindingBuilder
(resulting from forField call) I shall finally bind it in order to enable
the binder. But from javadoc I only see two bind methods: the first receives
the property name (not the case), the second a getter and a setter (unusable
since I have no bean), so how can I call the bind function? Note: also tried
a DynaBean but apparently it does not work.

[pinonpierre]

Another way to do that is to have an additional method to Binder.

For instance, for now, I have to do that:

Binder binder = new Binder();
binder.forField(textField)
   .asRequired("Required")
   .withValidator(new StringLengthValidator("Length Error", 3, 5 ))
   .bind(o -> textField.getEmptyValue(), null);

But ideally a noBind() method can be added:

Binder binder = new Binder();
binder.forField(textField)
   .asRequired("Required")
   .withValidator(new StringLengthValidator("Length Error", 3, 5 ))
   .noBind();

[stale[bot]]

Hello there!

It looks like this issue hasn't progressed lately. There are so many issues that we just can't deal them all within a reasonable timeframe.

There are a couple of things you could help to get things rolling on this issue (this is an automated message, so expect that some of these are already in use):

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Thanks again for your contributions! Even though we haven't been able to get this issue fixed, we hope you to report your findings and enhancement ideas in the future too!

[TatuLund]

This feature has been implemented as add-on in Directory https://vaadin.com/directory/component/fieldbinder