Happy Armistice Day, everyone.
I'm +1 on attaching so-called "preferences" to parcels (a la
PrefsForParcel).
The issue of preferences UI is interesting. I agree the current model
is frequently abused (in the email world, the extreme case is Eudora,
where the sheer number and variety of preferences panes is
overwhelming), and in most cases a direct manipulation model is
better. In defence of a preferences UI, I should say I think it can
sometimes _help_ discoverability: when I'm trying to figure out how a
new app works and what it does, I typically go through the menus, and
then the preferences. But maybe I'm just weird :).
--Grant
On Nov 11, 2005, at 12:22, Philippe Bossut wrote:
Hi,
First, I'd like to say +1 on this proposal though I'd like some
things to be clarified.
In general, a problem I always had with preferences is that it's an
amorphous aggregate of info without much semantic attached to it.
It rapidly becomes a clutter of everything no one knows exactly
where to fit. Preferences were invented to persist data between
sessions for document oriented applications that lacked a way to
persist their own data. In the context of Chandler, it's not a
problem we really have though we still need to persist things (I
won't call them preferences...) that are not user data per se (see
Jeffrey initial example in this thread).
Also, I know no one is advocating having UI for preferences (under
a "Preferences..." menu item), but, in case anyone has doubt, I
advocate against having a "Preferences..." menu item at all.
Preferences menu lead to countless discoverability issues. I'm of
the opinion that if a function foo is dependent of data "x", data
"x" should be available in the UI of function foo, not buried in
some obscure preference panel (you can tell I suffered through that
one, can you?... :) )
In general, I see 2 big types of preferences:
- state info: info that we want to persist between sessions (last
selected item, options chosen by the user in dialog x, prefered
behavior for action z...). Jeffrey's default folder for instance
falls in that category.
- style info: info that relates to how things are displayed (font
types, font size, colors, border info, etc...). Having a clear and
simple way to modify those in Chandler would indeed be a god send.
There may be other types.
User data (like account information for instance) are not
preferences but, well, user data. The criteria between preferences
and user data is that preferences can be purged or reset without
the user loosing anything or having to reconfigure anything. The
worst that could happen is that states and styles are lost. We
don't need for instance to implement schema evolution for
preferences but we do need to implement it for user data. That's
another criteria to semantically discriminate one from the other.
It's not always obvious. Consider that Mail.app for instance has
its UI to set up accounts under a Preferences... panel. Admitedly,
nixing accounts in an e-mail app is not semantically the same thing
that nixing the default e-mail font. Still, those 2 things are at
the same UI level. Bad, bad...
So I guess that my vote is +1 for having such a general mechanism,
assuming we don't call them indiscriminately "preferences" but
something else semantically meaningful (like "config" and "styles"
for instance, so that we really think about their semantic when
creating them) and that we don't take advantage of this to bury
important UI controls in hidden preferences panels... :)
Cheers,
- Philippe
Alec Flett wrote:
I think there's something to be said for exploring a somewhat
generic preferences architecture, or at the very least a set of
conventions - duck typing for preferences if you will (if it looks
like a preference, and acts like a preference, its probably a
preference)
In the mozilla project (full disclosure: I was the owner of the
preferences backend) we developed a system where all prefs are
stored in a central place, and each pref has its own name within
the a private namespace, such as "browser.cache.memory.enable".
3rd party plugins/extensions can "register" new prefs. This allows
for a particularly useful feature in mozilla, 'about:config' - go
ahead - type this into the URL bar in FireFox. What you'll get is
a UI to edit all global prefs across the system. Neat, huh?
However, I personally don't think that kind of system is quite
appropriate for a project like ours, especially given the dynamic
nature of both python and the repository.. but there are a few
things about the mozilla prefs system that were useful
specifically for preferences:
1) a global list of 'all preferences' so that they could be
reflected into the UI dynamically like about:config.
Of course, all of our repository can be reflected into the UI, but
I think there is value in distinguishing those values in the
repository that give some obvious, useful, and predictable change
in the behavior of the application.
2) the ability to register for changes to a preference, or a set
of preferences. This is useful because any one of a number of
actions could change the value of a preference, not just a
preferences dialog box.
For instance, you can register a callback for when the value of
"network.protocol-handler.external.mailto" changed, or for
"network.protocol-handler.external.*" to capture all sub-changes.
Both of these features are almost trivial given the repository.
I like philip's PrefsForMyParcel, and in fact I think we could
accomplish most of 1) and 2) by making a base Kind/class,
ParcelPrefs (or something..maybe just 'Preferences') that each
parcel could derive from, and declare new schema attributes to
store individual preferences. The KindCollection for ParcelPrefs
would then be the 'registry' of all prefs in the system.
the only trick at that point is the notification when preferences
change... but we have a number of systems for notifications, so
I'm willing to bet that would be fairly easy and we can address it
when there is actually a need.
Alec
Phillip J. Eby wrote:
At 08:57 PM 11/2/2005 -0800, Jeffrey Harris wrote:
Hi Folks,
What's our current thinking on how a developer should go about
establishing and using what I'll call a preference, essentially
a single
persistent value with a well-known name (in this case, I'm
wanting to
persist the last directories chosen for import and export)?
We've got lots of well-known collections living in
parcels/osaf/app/__init__.py, perhaps that's the appropriate
place for
preferences? It doesn't feel quite right to me...
I'm sending this question to the list instead of asking one
person or
another because
A) I think there might be different opinions, and
B) I'm hoping someone will write up a detailed example so that
knowledge
can live on in the list, not just my brain :)
The simplest thing that would work:
class PrefsForMyParcel(schema.Item):
some_pref = schema.One(sometype, defaultValue=something)
# ... other preferences
def installParcel(parcel, oldVersion=None):
PrefsForMyParcel.update(parcel, "prefs")
Accessing preferences can then be done via:
schema.ns("my.parcel", view).prefs.some_pref
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