NSOutlineView, NSTreeController and itemForPersistentObject...
-
Hello,
I'm running into yet more problems with
NSTreeController... It seems that this class is only
half-finished, but maybe I am wrong. The problem is
that when you use bindings with an NSOutlineView using
NSTreeController, the delegate and datasource methods
do not have direct access to the items held by
NSTreeController, which seems like madness to me...
For instance, if you hook up a datasource to an
NSOutlineView that uses bindings (eg. the one in the
OutlineEdit Core Data example) and then try to use a
datasource method such as
outlineView:persistentObjectForItem:, you will find
that the "item" object passed in is not the actual
object, but a proxy object of class
_NSArrayControllerTreeNode.
When I was experiencing a similar problem a few days
ago, Scott Stevenson on this list very helpfully
pointed out that the only way he knew around this was
to use an undocumented method, -observedObject.
Calling this on the item passed into outline view
datasource and delegate methods does indeed retrieve
the object.
However, I am now trying to get my outline view to
save its state using the datasource methods, and
whilst I can use -observedObject to get a persistent
object in outlineView:persistentObjectForItem:, there
is no way to use this information to restore things in
outlineView:itemForPersistentObject:, because
NSTreeController will expect this to return an object
of type _NSArrayControllerTreeNode - a private API
class.
It seems insane that using Core Data and bindings with
an outline view would prevent you from using any of
the useful datasource or delegate methods that call
for direct access to the item, but I cannot find
anything to solve this.
If anybody has delved into this, I would be very
grateful for some pointers.
Many thanks in advance,
Keith
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Hmm, I'm still having no joy with this... In the hope
that someone will soon start experimenting with
NSTreeController and run into the same problems, I've
described the problem in a little more detail here:
http://www.cocoadev.com/index.pl?OutlineViewCoreDataBindings
I've also filed a bug report, as it seems to me that
NSOutlineView's delegate and datasource methods
shouldn't be rendered unusable by using
NSTreeController and bindings...
If anyone here has played with NSTreeController and
outine views and managed to get the outline view to
save its state (and use other datasource/delegate
methods that use (id)item), I would be really grateful
if you could point me in the right direction, as I'm
sure I must be missing something here. At the moment,
it looks like I'm going to have to abandon
NSTreeController...
Many thanks,
Keith
--- Keith Blount <keithblount...> wrote:> Hello,
>
> I'm running into yet more problems with
> NSTreeController... It seems that this class is only
> half-finished, but maybe I am wrong. The problem is
> that when you use bindings with an NSOutlineView
> using
> NSTreeController, the delegate and datasource
> methods
> do not have direct access to the items held by
> NSTreeController, which seems like madness to me...
>
> For instance, if you hook up a datasource to an
> NSOutlineView that uses bindings (eg. the one in the
> OutlineEdit Core Data example) and then try to use a
> datasource method such as
> outlineView:persistentObjectForItem:, you will find
> that the "item" object passed in is not the actual
> object, but a proxy object of class
> _NSArrayControllerTreeNode.
>
> When I was experiencing a similar problem a few days
> ago, Scott Stevenson on this list very helpfully
> pointed out that the only way he knew around this
> was
> to use an undocumented method, -observedObject.
> Calling this on the item passed into outline view
> datasource and delegate methods does indeed retrieve
> the object.
>
> However, I am now trying to get my outline view to
> save its state using the datasource methods, and
> whilst I can use -observedObject to get a persistent
> object in outlineView:persistentObjectForItem:,
> there
> is no way to use this information to restore things
> in
> outlineView:itemForPersistentObject:, because
> NSTreeController will expect this to return an
> object
> of type _NSArrayControllerTreeNode - a private API
> class.
>
> It seems insane that using Core Data and bindings
> with
> an outline view would prevent you from using any of
> the useful datasource or delegate methods that call
> for direct access to the item, but I cannot find
> anything to solve this.
>
> If anybody has delved into this, I would be very
> grateful for some pointers.
>
> Many thanks in advance,
> Keith
>
> __________________________________________________
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Le 8 mai 05 à 15:22, Keith Blount a écrit :>
> If anyone here has played with NSTreeController and
> outine views and managed to get the outline view to
> save its state (and use other datasource/delegate
> methods that use (id)item), I would be really grateful
> if you could point me in the right direction, as I'm
> sure I must be missing something here. At the moment,
> it looks like I'm going to have to abandon
> NSTreeController...
>
> --- Keith Blount <keithblount...> wrote:
>
>> Hello,
>>
>> For instance, if you hook up a datasource to an
>> NSOutlineView that uses bindings (eg. the one in the
>> OutlineEdit Core Data example) and then try to use a
>> datasource method such as
>> outlineView:persistentObjectForItem:, you will find
>> that the "item" object passed in is not the actual
>> object, but a proxy object of class
>> _NSArrayControllerTreeNode.
>>
>> When I was experiencing a similar problem a few days
>> ago, Scott Stevenson on this list very helpfully
>> pointed out that the only way he knew around this
>> was
>> to use an undocumented method, -observedObject.
>> Calling this on the item passed into outline view
>> datasource and delegate methods does indeed retrieve
>> the object.
>>
>> However, I am now trying to get my outline view to
>> save its state using the datasource methods, and
>> whilst I can use -observedObject to get a persistent
>> object in outlineView:persistentObjectForItem:,
>> there
>> is no way to use this information to restore things
>> in
>> outlineView:itemForPersistentObject:, because
>> NSTreeController will expect this to return an
>> object
>> of type _NSArrayControllerTreeNode - a private API
>> class.
>>
Dear Keith,
I'm myself trying to use the combination NSOutlineView
+NSTreeController, but I'm not so advanced than you are, so my
comments may be of no help: I apologize in advance. (I have asked
myself a few questions recently on the list on this subject, but
didn't get any answer :-(.)
I tried using -observedObject and indeed it does work well. You can
silent the compiler warnings by putting these lines in your code:
@interface NSObject (privateAppkit)
-(id) observedObject;
@end
I have still to understand the complete connection between the
controller, when an NSTreeController is used, and the ouline view.
Anyway I use the tree controller also as a delegate, and it seems to
work perfectly. (I use a derived class implementing some of the
delegate methods). Apparently no data source is needed when using
Core Data.
For the -outlineView:itemForPersistentObject: problem, I have no good
solution. However, these methods only purpose is to save the expanded/
collapsed state of the items, right? So did you try to save this
state into the model, and use the delegate methods -
outlineViewItemDidCollapse: and similar to keep this state consistent
with the view?
Yours,
Thomas Lachand-Robert
********************** <tlr...>
<< Et le chemin est long du projet à la chose. >> Molière, Tartuffe. -
Keith,
I'm not quite sure what you're trying to accomplish here..
When using an outline view with bindings and core data, the tree
controller bound to your outline view provides the data, not the
datasource delegate. Since the default NSManagedObject
implementation does not have attributes to store the state of outline
view's nodes (if the node is expanded, if the node has children, if
it is a leaf node, etc.), this information is stored in a
NSArrayControllerTreeNode object that is wrapped around your
NSManagedObject or subclass.
If you're trying to read or restore the expanded or unexpanded state
of an outline view's nodes, you'll need to walk each node in the
outline view, get the corresponding persistent object using
observedObject, then query or set the nodes state by calling the
appropriate outline view methods with the node, such as
isItemExpanded:item, collapseItem:item, expandItem:item, etc.
Since NSOutlineView is a subclass of NSTableView, you can use
numberOfRows and itemAtRow:index methods to walk the outline view and
access it's nodes. You can either create an attribute to store this
state in your persistent object or store it externally.
Note: Each Core Data persistent object has an built-in read-only
"objectID" attribute that can be use to uniquely identify each
object. You can use this ID as a key to externally store the state of
each object node in your outline view.
- Scott
On May 7, 2005, at 1:06 PM, Keith Blount wrote:> Hello,
>
> I'm running into yet more problems with
> NSTreeController... It seems that this class is only
> half-finished, but maybe I am wrong. The problem is
> that when you use bindings with an NSOutlineView using
> NSTreeController, the delegate and datasource methods
> do not have direct access to the items held by
> NSTreeController, which seems like madness to me...
>
> For instance, if you hook up a datasource to an
> NSOutlineView that uses bindings (eg. the one in the
> OutlineEdit Core Data example) and then try to use a
> datasource method such as
> outlineView:persistentObjectForItem:, you will find
> that the "item" object passed in is not the actual
> object, but a proxy object of class
> _NSArrayControllerTreeNode.
>
> When I was experiencing a similar problem a few days
> ago, Scott Stevenson on this list very helpfully
> pointed out that the only way he knew around this was
> to use an undocumented method, -observedObject.
> Calling this on the item passed into outline view
> datasource and delegate methods does indeed retrieve
> the object.
>
> However, I am now trying to get my outline view to
> save its state using the datasource methods, and
> whilst I can use -observedObject to get a persistent
> object in outlineView:persistentObjectForItem:, there
> is no way to use this information to restore things in
> outlineView:itemForPersistentObject:, because
> NSTreeController will expect this to return an object
> of type _NSArrayControllerTreeNode - a private API
> class.
>
> It seems insane that using Core Data and bindings with
> an outline view would prevent you from using any of
> the useful datasource or delegate methods that call
> for direct access to the item, but I cannot find
> anything to solve this.
>
> If anybody has delved into this, I would be very
> grateful for some pointers.
>
> Many thanks in advance,
> Keith
>
>
>
> Yahoo! Mail
> Stay connected, organized, and protected. Take the tour:
> http://tour.mail.yahoo.com/mailtour.html
>
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Many thanks to you both for your replies. Surely this
is a lot of extra coding which could be avoided if the
datasource and delegate methods worked "correctly"? To
step through all of this just to save the state of an
outline view when you could just use a couple of lines
of code using the datasource methods seems to defeat
the "less code" philosophy of bindings... And even
going this route, you have to use -observedObject,
which is a hack because it is a private method.
Just because you use bindings, you should surely still
be able to use the datasource and delegate methods?
When using bindings with NSTableView through
NSArrayController, you can still use datasource and
delegate methods to provide drag'n'drop and persistent
state-saving functionality, so why should this be so
difficult with NSOutlineView? I still feel that there
should be a simpler solution, but it looks as though I
will have to go the route you suggest...
I think I need to play with this a bit more - maybe it
is just the Core Data part that is throwing me as I am
so new to it having only last week got my hands on
Tiger.
Many thanks again,
Keith
--- Scott Ahten <pixel...> wrote:> Keith,http://lists.apple.com/mailman/options/cocoa-dev/pixel%
>
> I'm not quite sure what you're trying to accomplish
> here..
>
> When using an outline view with bindings and core
> data, the tree
> controller bound to your outline view provides the
> data, not the
> datasource delegate. Since the default
> NSManagedObject
> implementation does not have attributes to store the
> state of outline
> view's nodes (if the node is expanded, if the node
> has children, if
> it is a leaf node, etc.), this information is stored
> in a
> NSArrayControllerTreeNode object that is wrapped
> around your
> NSManagedObject or subclass.
>
> If you're trying to read or restore the expanded or
> unexpanded state
> of an outline view's nodes, you'll need to walk each
> node in the
> outline view, get the corresponding persistent
> object using
> observedObject, then query or set the nodes state by
> calling the
> appropriate outline view methods with the node, such
> as
> isItemExpanded:item, collapseItem:item,
> expandItem:item, etc.
>
> Since NSOutlineView is a subclass of NSTableView,
> you can use
> numberOfRows and itemAtRow:index methods to walk the
> outline view and
> access it's nodes. You can either create an
> attribute to store this
> state in your persistent object or store it
> externally.
>
> Note: Each Core Data persistent object has an
> built-in read-only
> "objectID" attribute that can be use to uniquely
> identify each
> object. You can use this ID as a key to externally
> store the state of
> each object node in your outline view.
>
> - Scott
>
> On May 7, 2005, at 1:06 PM, Keith Blount wrote:
>
>> Hello,
>>
>> I'm running into yet more problems with
>> NSTreeController... It seems that this class is
> only
>> half-finished, but maybe I am wrong. The problem
> is
>> that when you use bindings with an NSOutlineView
> using
>> NSTreeController, the delegate and datasource
> methods
>> do not have direct access to the items held by
>> NSTreeController, which seems like madness to
> me...
>>
>> For instance, if you hook up a datasource to an
>> NSOutlineView that uses bindings (eg. the one in
> the
>> OutlineEdit Core Data example) and then try to use
> a
>> datasource method such as
>> outlineView:persistentObjectForItem:, you will
> find
>> that the "item" object passed in is not the actual
>> object, but a proxy object of class
>> _NSArrayControllerTreeNode.
>>
>> When I was experiencing a similar problem a few
> days
>> ago, Scott Stevenson on this list very helpfully
>> pointed out that the only way he knew around this
> was
>> to use an undocumented method, -observedObject.
>> Calling this on the item passed into outline view
>> datasource and delegate methods does indeed
> retrieve
>> the object.
>>
>> However, I am now trying to get my outline view to
>> save its state using the datasource methods, and
>> whilst I can use -observedObject to get a
> persistent
>> object in outlineView:persistentObjectForItem:,
> there
>> is no way to use this information to restore
> things in
>> outlineView:itemForPersistentObject:, because
>> NSTreeController will expect this to return an
> object
>> of type _NSArrayControllerTreeNode - a private API
>> class.
>>
>> It seems insane that using Core Data and bindings
> with
>> an outline view would prevent you from using any
> of
>> the useful datasource or delegate methods that
> call
>> for direct access to the item, but I cannot find
>> anything to solve this.
>>
>> If anybody has delved into this, I would be very
>> grateful for some pointers.
>>
>> Many thanks in advance,
>> Keith
>>
>>
>>
>> Yahoo! Mail
>> Stay connected, organized, and protected. Take the
> tour:
>> http://tour.mail.yahoo.com/mailtour.html
>>
>> _______________________________________________
>> Do not post admin requests to the list. They will
> be ignored.
>> Cocoa-dev mailing list
> (<Cocoa-dev...>)
>> Help/Unsubscribe/Update your Subscription:
>>
>>
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