set_sort_func

Sets (or unsets) the function used for sorting items.

If sort_func is null, all items are considered equal.

If the sort func changes its sorting behavior, gtk_sorter_changed needs to be called.

If a previous function was set, its user_destroy will be called now.

Parameters:

this	a `GtkCustomSorter`
sort_func	function to sort items
user_data	user data to pass to match_func
user_destroy	destroy notify for user_data