Re: Accessibility children: all or visible
Re: Accessibility children: all or visible
- Subject: Re: Accessibility children: all or visible
- From: Mike Engber <email@hidden>
- Date: Tue, 22 Apr 2008 13:51:46 -0700
Is it important that the Children attribute returns all the
children of a view, or would it be OK to return only the currently
available children? In my app getting all the children may be
pretty slow, while there are usually just a few child elements
visible at a time. The data is divided in pages, and the display
only reads the pages that are needed for display. Could I do the
same with the accessible children, and only return the children of
my view that are contained in the visible pages? Or doesn't
accessibility care too much about the visible area?
It is expected that all children would be returned from AXChildren.
There is an AXVisibleChildren attribute, but it is defined only for
AXRow/AXTableRow/AXOutlineRow, AXMenu, AXMenuBar, AXRadioGroup, and
AXList.
You might consider some sort of caching scheme. I know it can be
complicated to keep the cache current, but even if you have a very
conservative strategy it could be a big win. If you look at the
message pattern, you'll see the you're likely to be asked for the
children many times in rapid succession.
E.g. Even for something as simple as an assistive app trying to get
the description of the focused element (and it's one of your children)
- I'd guess that the children will be requested 2, 3 or more times.
So, even if you invalidate your cache at the drop of a hat (e.g. any
user action) - it could be a big win for typical interaction with an
assitive app.
Note, if don't return all your children, one problem (apart from not
conforming) scenario would be that you return a child, and then later
get that child handed back to you (e.g. for an attribute request) when
it's no longer visible. Depending on your implementation details, this
could mean that when the child comes back it's interpreted as a
completely different element. E.g. initially it was the 3rd visible
child, now, after scrolling the 3rd visible child is some other
element - doh!
-ME
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