Webkit GTK: Using the DOM Tree Walker

Question

So, I'm experimenting with Webkit GTK DOM functions. It's pretty straightforward, except for one thing: there's a useful part of the API called the WebKitDOMTreeWalker which, I assume, lets you walk over each node in the DOM, just like the TreeWalker object in Javascript.

Now, in Javascript a TreeWalker is created by calling:

document.createTreeWalker(root, nodesToShow, filter, entityExpandBol)

So, in WebKit GTK, there is an obvious counterpart in the API - a function called webkit_dom_document_create_tree_walker. The function signature is:

WebKitDOMTreeWalker* webkit_dom_document_create_tree_walker(WebKitDOMDocument* self, WebKitDOMNode* root, gulong what_to_show, WebKitDOMNodeFilter* filter, gboolean expand_entity_references, GError **error);

So creating a TreeWalker with WebKit GTK seems pretty straightforward - except for one big problem: the fourth argument in the webkit_dom_document_create_tree_walker expects a filter object, that is, it wants an instance of WebKitDOMNodeFilter. Well, the Javascript function also takes a filter, but you can pass null if you don't want to use a filter. With the Webkit API, passing NULL doesn't work. If you call:

WebKitDOMTreeWalker* walker = webkit_dom_document_create_tree_walker(doc, root, SHOW_ALL, NULL, false, err)

You get the error message:

** (webkit:3367): CRITICAL : WebKitDOMTreeWalker* webkit_dom_document_create_tree_walker(WebKitDOMDocument*, WebKitDOMNode*, gulong, WebKitDOMNodeFilter*, gboolean, GError): assertion `filter' failed

So, the WebKit API won't accept a NULL pointer for the filter argument. Evidently you need to pass an instance of a WebKitDOMNodeFilter. Okay, again - this wouldn't be a problem either, except I've searched far and wide through the WebKit API, as well as Google, and I can't find anyway to create a WebKitDOMNodeFilter object! The header file for WebKitDOMNodeFilter.h doesn't expose any constructor for WebKitDOMNodeFilter. It seems like the API doesn't ever expose anyway to actually construct a WebKitDOMNodeFilter object at all.

Yet... the API exposes many functions (like webkit_dom_document_create_tree_walker, and webkit_dom_document_create_node_iterator) which require a WebKitDOMNodeFilter. So... is the API just incomplete right now? Or, is there some way to create a Filter object which I'm just not seeing?

Answer 1

Can you try casting your null to the WebKitDOMNodeFilter type by calling WEBKIT_DOM_NODE_FILTER(null)?