How to make a wicket component that's re-rendered on every AJAX request to a page?

Is there a way to make a Wicket component re-render itself on every AJAX request to a page? (Essentially to do what ajaxRendered="true" does in RichFaces.)

My application basically consists of the following:

• An editable datagrid records changes the user is doing
• These changes are stored in the session
• There are buttons to save the changes or to undo them.

The save and undo buttons should be enabled or disabled dep开发者_JAVA百科ending on if there are any recorded changes or not. Since there's several ways to input changes (editing, importing a CSV, etc.), I want to avoid having to intercept every action that might change the saved state.

Also, the buttons are only shown on some pages, so I don't want to have to sniff them in the page in a custom WebRequestCycle.

Is there a hook that Wicket calls when an AJAX request is about to be processed, that's called for every component on the page? I know there's Component#onBeforeRender() and Component#onConfigure(), but the documentation for them doesn't state when they're called for AJAX requests.

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In Wicket 1.5 there is an event bus. For each Ajax request an event is sent to each component and the component can use AjaxRequestTarget to add itself for re-render.

E.g.:

class MyComponent ... {

 public void onEvent(Object payload) {

   if (payload instanceod AjaxRequestTarget) {
     ((AjaxRequestTarget) payload).add(this);
   }
 } 

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I was having a similar problem and thought of two possible solutions from which I used the second one.

1. Call a method on your page in the Ajax-Handler, which in turn invokes a visitor to find all childs that need to be rerendered, adding them to the target.

2. A variation of the observer-pattern... I had my components register themselves as wantToUpdate at the page and triggered a function, adding them all to the Requesttarget in my Ajax-Handler. I couldn't use the observer pattern out of the box since my components don't know each other and I didn't want to introduce this kind of coupling.