使用AJAX / XMLHttpRequest时不调用shouldStartLoadWithRequest

I am trying to send method invocations from JavaScript to Objective-C and vice versa. Everything works fine for window.location triggered urls, which are catched by shouldStartLoadWithRequest. Now if I try to use an AJAX call instead, shouldStartLoadWithRequest is not called. Is there a way to do this? Mainly I do not want to be restricted to the max URL size on data that can be passed from JavaScript to Objective-C.I am trying to send method invocations from Jav