Function c4queryobs_create 

pub unsafe extern "C" fn c4queryobs_create(
    query: *mut C4Query,
    callback: C4QueryObserverCallback,
    context: *mut c_void,
) -> *mut C4QueryObserver

Creates a new query observer, with a callback that will be invoked when the query results change, with an enumerator containing the new results. \note The callback isn’t invoked immediately after a change, and won’t be invoked after every change, to avoid performance problems. Instead, there’s a brief delay so multiple changes can be coalesced. \note The new observer needs to be enabled by calling \ref c4queryobs_setEnabled.