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From Noel Grandin <noelgran...@gmail.com>
Subject Re: [RFC] Selection change events
Date Fri, 25 Jun 2010 08:25:17 GMT

I think your change is a good idea, but I don't really like using null
as an indicator of something special.
It sounds like an invitation to make mistakes about when the parameter
is or is not useful.

Why don't we just make this a special case and drop the "previous"
I can't see many callers wanting to make use of it, and they could
always keep track of it themselves if they really need to.

-- Noel

Greg Brown wrote:
> Hi all,
> I am thinking about making a change to how selection change events are fired and I would
like to hear your feedback. Currently, selection change events are fired only when an explicit
call has been made that affects the selection. 
> For example, in ListView, calling either setSelectedRanges() or clearSelection() will
fire this event. However, an operation that indirectly changes the selection state (such as
adding or removing an item from the ListView's model data) does not trigger an event. This
was originally done by design - selectedRangesChanged() includes the previous selection as
an argument, and we didn't want to have to manually re-construct that every time the selection
changed as a side effect of a model change:
>   public void selectedRangesChanged(ListView listView, Sequence<Span> previousSelectedRanges);
> However, in practice, I have found this to be a bit challenging. More than once I have
registered a selection change listener expecting to receive notification of all selection
changes, forgetting that it is not designed that way. If I am getting tripped up by this,
I'm guessing that other developers might be as well.
> So, I am proposing that components that maintain a selection state also fire selection
change events when the selection changes indirectly. In this case, a null value would be passed
for the previous selection. This will save the effort of re-constructing the previous selection
info and will give the listener additional information about the nature of the change (i.e.
null == indirect state change).
> Please let me know what you think.
> Thanks for your input,
> Greg

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