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.
Chandler's repository already provides a great way to persist user data,
state between sessions and a host of other stuff in the system (e.g. the
order of items in tables), which we already use everywhere and it works
great. I think calling all of this persistent data "preferences" would
be confusing. I like Philippe's suggestion (see below) that we call user
settings (e.g. style information) preferences. Of course they get
persisted in the repository like all the other state and maybe the only
thing that makes them different is how you find them, that they are
associated with a parcel, and what kind of information is stored there.
- 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
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Open Source Applications Foundation "Dev" mailing list
http://lists.osafoundation.org/mailman/listinfo/dev
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Open Source Applications Foundation "Dev" mailing list
http://lists.osafoundation.org/mailman/listinfo/dev
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Open Source Applications Foundation "Dev" mailing list
http://lists.osafoundation.org/mailman/listinfo/dev
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Open Source Applications Foundation "Dev" mailing list
http://lists.osafoundation.org/mailman/listinfo/dev
