Passing values between classes in Vaadin - vaadin

Question

This might be more of a Java question, but how would you access values (say from a textfield) of a given view/class from a different class? For example if there was a TextField t1 that is in the MainView, and I wanted to get its current value for a computation in a different class. And is there a more Vaadin-specific approach here?

Answer 1

That can depend on the use case specifically. Since you mentioned a TextField value I assume the value is not yet stored in the DB, it's just on the UI yet -> I rule out singleton spring services.
A few ideas:
If the MainView and the different class are nested components and it's viable and not really complicated across a lot of classes... then probably passing it down the way when creating the sub-component. This is a naive solution - it can get pretty messy.
MainView() {
var t1 = new TextField();
var d = new Different(t1);
}
Fire and listen to Vaadin Component events. If you want really loose coupling, the most universal would be to use the UI instance as the event bus.
// listen in different class
ComponentUtil.addListener(attachEvent.getUI(), CloseMenuEvent.class, e -> closeMenu());
// fire change in MainView
ComponentUtil.fireEvent(ui, new CloseMenuEvent(ui))
A more specific version of number 2. is to pass the ValueChangeListener of the MainView's t1 to the different class.
MainView() {
var t1 = new TextField();
var d = new DifferentClass();
t1.addValueChangeListener(d::t1Changed)
add(t1, d);
}
Extract the common field to a third party, to a third class. Use a #UIScoped spring bean (#SpringComponent, #Service, ...) that will hold that field, and inject it to both MainView and the different class.
#Route
public class MainView extends VerticalLayout {
public MainView(Model m, Different d) {
add(m.t1, d);
}
}
#Scope(SCOPE_PROTOTYPE)
public class Different extends Component {
public Different(Model m) {
// something with m.t1
}
}
#UIScoped
public class Model {
public final TextField t1 = new TextField(); // TODO use getter
}
You could change the 4th approach by keeping String in Model and having a value change listener that updates it.