Can't submit on dropdown lazy loading - wicket

Question

My form has 1 dropdown use AjaxLazyLoadPanel and 1 ajax button submit.
I click button submit that works only when the dropdown is finished loading.
Index.java
form.add(new AjaxLazyLoadPanel("lazy") {
private static final long serialVersionUID = 1L;
#Override
public Component getLazyLoadComponent(String markupId) {
Fragment fr = new Fragment(markupId, "lazyContentFragment", Index.this);
fr.add(dropdown());
return fr;
}
});
form.setOutputMarkupId(true);
form.add(new AjaxButton("search") {
#Override
protected void onError(AjaxRequestTarget target) {
target.add(feedback);
}
#Override
protected void onSubmit(AjaxRequestTarget target) {
//do something...
}
});
Index.html
<form wicket:id="form">
<input wicket:id="textbox"/>
<div wicket:id="lazy"></div>
<button wicket:id="search"></button>
</form>
<wicket:fragment wicket:id="lazyContentFragment">
<select wicket:id="dropdown"></select>
</wicket:fragment>
Is there any way to submit the form without waiting for the dropdown finish loading.

Answer 1

By default wicket-ajax.js serializes the Ajax calls to the server. This is being done so that the second Ajax call is not called if its HTML element is being removed/painted by the first Ajax call.
In addition only one thread can manipulate a Page instance at a time at the server side!
To be able to make two Ajax calls at the same time you need to use different AjaxChannels for them. For example:
... = new AjaxButton("someId") {
#Override protected void updateAjaxAttributes(AjaxRequestAttributes attributes)
{
attributes.setChannel(new AjaxChannel("customName"));
}
}
This way both Ajax requests will be fired to the server, but the AjaxButton's one will be processed only after the AjaxLazyLoadingPanel's one releases the lock on the page instance at the server side. There is no way to execute two threads on the same page instance (i.e. having the same pageId).

Answer 2

If you're dropdown's choices are taking so long to load, you might want to make your AjaxLazyLoadPanel asynchronous by overriding #isContentReady():
private String token;
private List<T> choices;
protected boolean isContentReady()
{
if (token == null) {
token = startLoadingChoices();
} else {
choices = checkChoicesLoaded(token);
}
return choices != null;
}
Since Wicket manages and serializes all pages, your page must not be held as a reference in a thread or a listener in central registry. Keep a token instead and ask for the loading result; #isContentReady() will be polled repeatedly until it returns true.