Opening a modal panel depending on a server-side decision. How?

Question

Hi,
Short version: How can you conditionally open a Richfaces modal panel (or, for that matter, perform any other action) on the client, depending on the (boolean) outcome of a server-side method?
Long version: I have a form which, among others, contains an address, which needs to be checked against a geo database, in order for the coordinates (latitude/longitude) of that address to be added. Now the thing is, if there is no 100% match (e.g. due to a misspelling or if there are many names for the same town) only the zip codes are matched, and there are zip codes that cover many towns or small villages. In that case, I'd like to popup a modal panel with all the towns/villages with that zip code, so that the user can choose the one that is actually meant. If there is a single exact match (or if the address was not changed at all -- there is also other data on the form) then nothing should popup and the form data just saved as usually.
What I've tried so far is to bind the submit button to an action method that checks the address and if it's all OK saves the form data to the DB and sets a bean property to false (meaning "no popup"). If there are multiple choices for the address, then the bean does nothing but set the bean property to true (do popup) and return. Then on the client, the modal panel's rendered attribute is bound to that boolean property, so that it is rendered or not as appropriate. Finally, the submit button (which is an <a4j:commandButon>) is set to reRender the modal panel on completion of the submit request, so that the bean property is re-evaluated.
On theory, this should work. (Or am I missing something?) However, the modal panel just does not pop up, no matter what I do (the business logic itself with saving and matching and stuff works fine). Are there any other ideas about how this behavior could be achieved? Am I missing some point?
Any comments or ideas are appreciated!
Greetings,
Mike

Answer 1

you can use this:
<a4j:commandButton data="#{mybean.mybool}"
                   oncomplete=" if (data == true) {
                                   #{rich:component('mymodalpanel')}.show()
                                } else {
                                   return false;
                                }" />