[Usability] Using checkbuttons, but needing three states...

[Vincent Untz <vuntz gnome org>]

Hi,

In pessulus (a lockdown editor I'm writing), I'm using checkbuttons to
configure some boolean settings. This sounds logical and it doesn't look
like there's a problem. But there is :-)

In GConf, there can be three states for a boolean key: true, false and
unset. Most of the times, we don't care about unset since if the key is
unset, a default value will be used. But with pessulus, that's a
different matter: it can configure a mandatory value for a key. Eg, it
can set the mandatory value of /apps/epiphany/lockdown/disable_history
to TRUE to force the disabling of history of epiphany, to FALSE to force
the use of history. And if it sets this key to unset, then the user will
be able to choose what he wants.

So the three states are useful. But how can I do this with checkbuttons
in a non-confusing way? I can set the checkbutton to the "inconsistent"
state if the key is unset, but I feel it's confusing and not really
understandable.

Another possibility would be to consider that only one of TRUE/FALSE is
useful for lockdown and that when the useless value is chosen, the key
is unset. For example, I don't think that, in the previous example, the
FALSE value is really useful... It's probably the easier, but I have the
feeling that it won't be always possible.

What do you think?

Vincent

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