Wicket Dependency Injection

Question

I've got a page with a form in Wicket where the form requires a collaborator to get its job done. The collaborator is injected (for which I'm using Guice) and looks something like:

public class RegistrationPage extends WebPage {
    @Inject
    public RegistrationPage(RegistrationService service) {
        this.service = service;
        add(new RegistrationForm());            
    }

    private class RegistrationForm extends Form {
        public RegistrationForm() {
            // setup
        }

        protected void onSubmit() {
           service.doSomething();
        }
    }
}

I don't like the idea that the RegistrationService is injected into the RegistrationPage when it's just the RegistrationForm that needs it. I could change the RegistrationForm to receive the RegistrationService:

public RegistrationForm(RegistrationService service) {
    this.service = service;
}

and remove the field from the RegistrationPage, but the RegistrationPage is still being used to do the pass-through.

I guess what I'm asking is what the best-practise is for doing this? Is this ok to do, or would it perhaps be better to inject the RegistrationForm itself into the Page:

   public class RegistrationPage extends WebPage {
        @Inject
        public RegistrationPage(RegistrationForm form) {
            add(form);
        }
   }

   ---

   private class RegistrationForm extends Form {
        private RegistrationService service;

        @Inject
        public RegistrationForm(RegistrationService service) {
            this.service = service;
        }

        protected void onSubmit() {
           service.doSomething();
        }
    }

I'd prefer this as I'd like to have the RegistrationForm in a separate class/file. I'm quite new to Wicket so unsure of what the norm is - can someone show me the guiding light? :)

Answer 1

the basic paradigm with wicket+ioc is: most dependencies should be injected via setter injection. constructor injection is impossible for WebPages.

components/panels/forms/pages should only be on the recieving end.

so, inject the dependency to RegistrationService happily into the RegistrationForm , then create it in the RegistrationPage with add(new RegistrationForm());

wicket has IComponentInstantiationListener - one of them is guice. they get notified during the constructor of each component/webpage. so your RegistrationForm will have its dependencies injected before any part of your code can execute.

the way i would do it: (of course RegistrationForm can be in another file)

public class RegistrationPage extends WebPage {

@Inject
public RegistrationPage() {
    add(new RegistrationForm());            
}

---
private static class RegistrationForm extends Form {
   RegistrationService service;

      @Inject
     public void setRegistrationService (RegistrationService  service){
     this.service = service;
        }
    public RegistrationForm() {
        // setup
    }

    protected void onSubmit() {
       service.doSomething();
    }
}
}

if you decide to put the RegistrationForm inside the Page as inner class, remember to declare it static! you will most likely not need any references to the enclosing class.