RenderHead is not called

Question

I have a CloakDecorator class that implements IAjaxCallDecorator and IHeaderContributor :

 public class CloakDecorator implements IAjaxCallDecorator, IHeaderContributor { @SuppressWarnings("unused") private static final ResourceReference INDICATOR = new ResourceReference(CloakDecorator.class, "indicator.gif"); private static final ResourceReference JS = new JavascriptResourceReference(CloakDecorator.class, "CloakDecorator.js"); private static final ResourceReference CSS = new ResourceReference(CloakDecorator.class, "CloakDecorator.css"); public CloakDecorator() { System.out.println("Constructor"); } public void renderHead(final IHeaderResponse response) { System.out.println("renderHead"); response.renderCSSReference(CSS); response.renderJavascriptReference(JS); } @Override public CharSequence decorateScript(CharSequence script) { return script; } @Override public CharSequence decorateOnSuccessScript(CharSequence script) { return script; } @Override public CharSequence decorateOnFailureScript(CharSequence script) { return script; } } 

Now from AjaxLink I create an instance of CloakDecorator :

 AjaxLink link=new AjaxLink("") { @Override public void onClick(AjaxRequestTarget target) { } @Override protected IAjaxCallDecorator getAjaxCallDecorator() { return new CloakDecorator(); } }; 

The problem is that the CloakDecorator constructor is being CloakDecorator , but the renderHead method renderHead not being called. What am I doing wrong? I put some System.out.println in the constructor and in the renderHead method, the System.out.println constructor works, but the second doesn't.

Answer 1

Unfortunately, just implementing the IHeaderContributor does not guarantee that you are really contributing to the page / component header. This only works for instances of Component and IBehavior elements that are added to the page and to the page. Specifically from javadoc IHeaderContributor :

 An interface to be implemented by components or behaviors that wish to contribute to the header section of the page. 

The specific code that causes this is in Component#renderHead(HtmlHeaderContainer) . It checks to see if IHeaderContributor implements itself and any of its behavior, and then adds these contributions.

To solve your problem, you can:

• You have an AjaxLink IHeaderContributor
• Add IBehavior to your AjaxLink that implements IHeaderContributor

Depending on how often you use this, option # 1 may be the best. Create a "CloakedAjaxLink" that will do everything you need.

Answer 2

Since Wicket 1.5 IAjaxCallDecorators can also contribute to the header if they implement IComponentAwareHeaderContributor.

Answer 3

I think you need to add the IHeaderContributor component to the component so that it actually “contributes” to the document. The way you use it, you use only half of the required implementation. I suggest you split your implementation or write CloakLink, including this code that can contribute to the page where it is added.