Re: [Adobe-source-devel] Disabling buttons

[Ralph T. <ra...@gm...>]

can_do_element_operation is in the invariant section, meaning that it
should be true.

I think what happens is:

  * When "selection == @item_end" the invariant can_do_element
operation is not satisfied
  * "selection" caused to an invariant violation.
  * .._params are dictionaries, all of which reference "selection"
  * the buttons are bound to the .._params which contain a cell
contributing to an invariant violation and are disabled.

It seems like if a dictionary contains any cell which contributed to
an invariant violation then anything bound to the dictionary is
disabled.

Ralph

On Apr 2, 2005 4:08 PM, David Catmull <unc...@un...> wrote:
> I'm trying to understand how the list_box_emulator example works as far
> as disabling the Insert and Delete buttons.
> 
> There is a 'can_do_element_operation' in the sheet, and yet it is not
> referenced anywhere. It looks like the buttons are being disabled
> because they are bound to 'insert/delete_params' which both reference
> 'selection' which is referenced in the invariant, but I still don't
> quite follow how that works. What exactly is the connection between
> 'insert/delete_params' and 'can_do_element_operation'? Is it just the
> fact that 'selection' is in the definition of
> 'can_do_element_operation'?
> 
> --
> David Catmull
> unc...@un...
> http://www.uncommonplace.com/
> 
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