Re: [lmi] switch census view to use wxDataViewCtrl

[Václav Slavík]

Hi,

On 3 Aug 2011, at 16:22, Greg Chicares wrote:
> My answer to both questions is that we needn't go against the standard
> convention--as long as some row always has "command focus", so that commands
> always operate on some row...if that is possible with wxDataViewCtrl, which
> I suspect it might not be.

It almost certainly is possible (you can set selection to something as soon as 
you detect that the selection became empty), but as Vadim noted, it may be 
better not to. It's not native behavior and it's IMHO quite surprising when 
such thing happens.

I think it should be left to behave natively, i.e. make it possible to deselect 
everything. Note that it's not really an issue in practice: as soon as you hit 
an arrow key (without modifiers), focus moves to a new item and selection is 
set to equal the focus.

> Originally, years ago, class CensusView (or its predecessor) used a single-
> selection control. We changed that only to permit deletion of multiple cells;
> and deletion is the only operation for which multiple selection matters. But
> having zero cells selected makes no sense for deletion, or for any other
> operation. For example,
>  File | New | Census
>  Census | Delete cell(s)
> produces this messagebox:
>  Confirm deletion
>  Irrevocably delete 0 of 1 cells?
>  Yes   No
> which looks like a logic error. ("Obviously that's a no-op, so why ask me to
> confirm whether or not I want to do...nothing?") In that testcase, the first
> (and only) cell has the "focus rectangle" but no "selection highlight", and
> menu commands do not apply to it: that's the regression I want to fix, and
> I'm guessing that to do so we need (at least) one row to have "selection"
> as well as "focus".

Yes. But I think the right thing would be disable all these commands if there's 
no selection, thus making the above situation impossible -- just as some 
commands are disabled in case of multiple selection now. I consider it 
preferable to doing unexpected things with the selection.

I'd also modify the Delete cell(s) operation to set selection to something 
reasonable after it's done -- that's the only (or in any case, the most common) 
case when you can end up with empty selection without doing it intentionally. 
And it does make sense to select the first row that will now occupy the place 
of deleted rows.

> It was possible (but, importantly, more difficult) to get that "delete 
> nothing?
> messagebox with a wx-2.9.0 version of lmi, by doing Ctrl-left_click on the 
> last
> selected row...so this is an old lmi anomaly that's just more likely to arise
> with the wxDataViewCtrl implementation.

That's why I think we should disable the commands instead. Playing tricks with 
the selection risks to leave some way to trigger this open.

> Also, again with an older version, if I
> make a census with two cells, select the second, and then unselect so that it
> keeps the focus rectangle...and then do "Census | Edit cell", it's the 
> (unfocused)
> first cell that's edited, not the second; shouldn't the focused cell have been
> used in the listview implementation, or do I still misunderstand how this 
> works?

The focus is really only for keyboard navigation and it's only use (in listview 
or currently; it will be useful for navigation within wxDVC columns later) is 
to select multiple non-neighbouring items via Ctrl-arrows and Space. It doesn't 
take the role of selection even in absence of "real" selection.

Regards,
Vaclav