Is there a way to add a something like a value change listener on specific field in binder?

Question

I need to add a reaction in my interface on changes in TextField and ComboBox.

Binder is a convinient way for handling data binding in Vaadin.

I can't use on textField.addValueChangeListener(...) as it is called before new value is set in binded model.

Is there a way to add a something like a value change listener on specific field in binder?

I can use binder.addValueChangeListener() but it is fired on every bound field changes and I can't easily tell them apart.

Ideally, it would be something like that:

binder.forField(specificTextField)
    .withConverter(...)
    .withValidator(...)
    .bind(Person::getName, Person::setName)
    .addValueChangeListener(...); // nonexistent functional

Answer 1

The answer to the question whether there is a way to add a value change listener to a single Binding itself is no there is not. I agree this could be a cool and useful addition to the Flow API. Please go ahead and write an issue in their github

However, as you noticed yourself, there is the method Binder::addValueChangeListener, and there is a way to tell them apart. The accepted eventListener has a way to get the HasValue (a.k.a. bound input field) that fired the change event. it also has access to both the old and the new value.

TextField tf = new TextField();
ComboBox cb = new ComboBox();
// todo: binding of fields

binder.addValueChangeListener(valueChangeListener -> {
    if(valueChangeListener.getHasValue().equals(tf)){
        // tf value changed
    } else if(valueChangeListener.getHasValue().equals(cb)) {
        // cb value changed
    }
}