On 7 mai, 23:14, Ed <[email protected]> wrote:
> Hellu,
>
> I am trying to get a better understanding of the event bubbling and
> canceling an event:
> 1) Does all gwt events bubble up? even if the parent itself doesn't
> support the gwt event?
http://code.google.com/webtoolkit/doc/1.6/FAQ_UI.html#How_can_I_efficiently_handle_events_from_many_interior_Widgets?
links to PPK's excellent writeup on the subject.
See also http://www.slideshare.net/pp.koch/voices-that-matter-javascript-events
...and the answer is "no", not all DOM events bubble; and AFAICT GWT
doesn't bubble "logical" events.
> So a Panel should receive the focus event of contained textbox?
no, because the focus event doesn't bubble.
> 2) Suppose I have panel with a textbox and I am the only one that add
> a listener to the textbox. Is it safe and better to call
> event.stopPropagation() in the listener in this case?
> With safe I mean; does anybody else might need the event, like for
> example the KeyUpEvent, that I cancel? (maybe the (root) browser-
> display itself .......
Someone could always use the capture phase (NativePreviewEvent/
NativePreviewHandler) and see the events, so calling stopPropagation
isn't probably worth it.
> Any idea about the performance difference if you have "many" widgets
> in case you cancel the event?
I do believe bubbling is somehow optimized by browsers, as this is the
"normal" behavior; so I doubt stopPropagation would really make a
difference (though I have no numbers).
More importantly, I think you should only use stopPropagation on
purpose, to make your code easier to understand, thus to maintain (uh,
why did I prevent bubbling of this event 2 months ago? there must have
been a good reason, but which one?).
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