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.