Hi Jake,
Unfortunately the DOM structure is bound more to the JavaScript way of doing
things than Widgets. In
JavaScript you can't have more than one event listener (of a given event type)
per element, while
Widgets may have any number.
So to work around this: GWT Widgets are the only listeners on their nested
Element object (notice
they implement the com.google.gwt.user.client.EventListener interface). SO when
they receive an
event from the browser, they decode it into a DOMEvent and dispatch it to all
the Handlers
registered for that Widget.
Unfortunately there is no simple way to deal with this on the DOM nodes
themselves, and in
particular there is no simple way to deal with IFrame loading events. If you
take a look at how
FormPanel receives loading events from it's hidden IFrame there are two
different implementations
(one for IE6, and the generic implementation).
For normal browsers(com.google.gwt.user.client.ui.impl.FormPanelImplIE6), the
event is hooked using:
iframe.onload = function() {
IE6 (com.google.gwt.user.client.ui.impl.FormPanelImplIE6) looks like:
iframe.onreadystatechange = function() {
if (iframe.readyState == 'complete') {
Both implementations also ensure that they "unhook" the events, by assigning
the listener function
to null (see FormPanel.onAttach / onDetach). I would consider extending the
Frame Widget rather than
using the DOM api directly. Widgets provide loads of useful safety nets that
you otherwise need to
write yourself (including attaching multiple Handlers to the element).
Hope this Helps.
//J
Jake wrote:
> Hi all,
>
> I just have a quick question: I know that GWT presents a fairly low-
> level DOM API that wraps native DOM objects. What I'd like to do is
> create a new iframe element, and then set a DOM onLoad listener on it
> so that I can then manipulate the iframe's internal document (its
> contentDocument). It's very easy for me to imagine how to implement
> this, except for the fact that I cannot find a way to set any kind of
> a listener on any of the DOM objects exposed by GWT. I found some blog
> posts that mentioned that GWT's method of event handling had changed
> in 1.6 [0][1], but I'm not sure if that applies only to classes that
> extend Widget, or to the wrapped DOM objects as well. Hopefully I'm
> just missing them.
>
> I'd greatly appreciate any guidance anyone can offer. Thanks,
>
> Jake
>
> [0]
> http://lemnik.wordpress.com/2009/03/04/gwts-new-event-model-handlers-in-gwt-16/
> [1] http://lemnik.wordpress.com/2009/03/12/using-event-handlers-in-gwt-16/
> >
>
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