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Re: Implementing NSOutlineView autosaveExpandedItems with CoreData

Hi Ian,

I've got a CoreData object graph with an outline view showing instances of an NSManagedObject subclass called "Group".
The Group class has the standard to-one relation 'parent' and to- many 'children'.
The outline view is working perfectly.

I've set autosaveExpandedItems to YES and when I expand or unexpand (contract?) a group my outline view's data source gets sent the persistentObjectForItem message. 

Collapse is the word used in the docs.

I can see in the prefs plist for my app that the expanded Group itmes are being saved, and when my application launches, the outline view's data source object gets sent the itemForPersistentObject message.

Below is what I'm doing for each of these messages:

- (id)outlineView:(NSOutlineView*)outlineView persistentObjectForItem:(id)item
{
NSNumber *uid=[[item representedObject] valueForKeyPath:@"uid"];
id archivedObject=[NSKeyedArchiver archivedDataWithRootObject:uid];
return archivedObject;
}

- (id)outlineView:(NSOutlineView *)outlineView itemForPersistentObject:(id)object
{
NSNumber *uid=[NSKeyedUnarchiver unarchiveObjectWithData:object];
NSManagedObjectContext *context=[self managedObjectContext];
NSFetchRequest *request=[[NSFetchRequest alloc] init];
NSEntityDescription *groupEntityDescription=[NSEntityDescription entityForName:@"Group" inManagedObjectContext:context];
[request setEntity:groupEntityDescription];
NSPredicate *predicate=[NSPredicate predicateWithFormat:@"uid== %@",uid];
[request setPredicate:predicate];
NSError *error;
NSArray *fetchResults=[context executeFetchRequest:request error:&error];
if ([fetchResults count])
return [fetchResults objectAtIndex:0];
return nil;
} 

The request object is not being released.

The persistentObjectForItem method successfully archives and returns the 'uid' property for the item's represented object - this is a unique identifier for each of my Groups.

The itemForPersistentObject successfully reconstitutes the archived uid and correctly finds the Group with the unique 'uid' property and returns it.

Expanded items in the outline view are not being restored however.

Is itemForPersistentObject expecting me to return something else?
My guess would be that it was expecting an instance of NSTreeNode, since this is what I first got as 'item' in persistentObjectForItem.
Sadly though, I can't see a way to get an NSTreeNode from an object.
I have [item representedObject] for archival, but not [object representingItem], if you see what I mean.

Obviously I've tried returning an the 'item' archived but it doesn't respond to archiving.
Neither (obviously) does my NSManagedObject subclass... should I implement archiving in my subclass to get this to work?

Does anyone have any clue they can distribute my way? (citation: http://www.bofhcam.org/co-larters/distributing-clue/index.html)
I've seen lots in the usual places (lists.apple.com, cocoabuilder.com et al) about this but no actual solutions shout out at me. Perhaps I'm not looking hard enough. (most likely).

Many TIA
Ian

I have this working in my app and I'm doing almost exactly the same thing. I'm also using the UID as the persistent object so you don't have to return an archived version of your whole model object or the tree node.

I would check two things:

1. Are you setting the autosaveName to the outline view?

2. Maybe the outline view is trying to restore the expanded state before your tree controller has content? You said itemForPersistentObject returns the correct Group, but this actually happened to me before, so just making sure :)

Beyond those two, if you still can't figure out why it's not working, saving and restoring expanded state of an outline view is a trivial task. I use the following bit of code in an NSOutlineView subclass to do just that:

- (id)expandedState
{
NSMutableArray *state = [NSMutableArray array];
NSInteger count = [self numberOfRows];
for (NSInteger row = 0; row < count; row++) {
id item = [self itemAtRow:row];
if ([self isItemExpanded:item])
[state addObject:[[self dataSource] outlineView:self persistentObjectForItem:item]];
}
return state;
}

- (void)setExpandedState:(id)state
{
if ([state isKindOfClass:[NSArray class]] == NO) return;

// Collapse everything first
[self collapseItem:nil collapseChildren:YES];

for (id pobj in state) {
[self expandItem:[[self dataSource] outlineView:self itemForPersistentObject:pobj]];
}
}

You can use those two methods to save the expanded state to the user defaults and then restore later on exactly when you need to.

- Andy Kim

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