Why is my NSOutlineView datasource nil?

Question

This is a follow-on question from my previous one relating to why my managedObjectContext was returning to nil. I thought the direction of the question would get buried in the old one.

I now get my mangedObjectContext to not return nil and when performing [outlineView reloadData], nothing at all happens to my outlineView. I tried selectively removing parts of the code that are intended to update the outlineView to see if anything changes and the answer is no. I've since found out (after I wrote this question originally) that my dataSource association is disappearing at some stage.

Notes:

• the code included below is run once on awakeFromNib of the datasource class and works perfectly.
• It is on calling it at any other time that my problem arrises. I get no errors debugging but my outlineView remains unchanged.
• I narrowed this down to running on NSLog of [outlineView dataSource]. When the method is called from awakeFromNib it returns the dataSource as being my dataSourceClass correctly. Every other time it returns the dataSource as nil.
• the dataSourceClass was bound to the outlineView in InterfaceBuilder.
• All other NSLog checks I've made to object updates in arrays of my code comes back as expected with correct updates. In fact, I checked the final projectsArray and clientsArray and they contain all new objects introduced before attempting to create nodes in the outlineView.
• I'm using the standard xcode generated core data app delegate code.
• I'm not using NSTreeController and using my own NSOutlineViewDataSource. It was not possible (or not documented) on how to populate an outlineView based on the parent/child relationships of two core-data entities.
• I'll also include my NSOutlineViewDataSource code below.

Updates:

Update 1: Hmmm... just before I call [outlineView reloadData] I tried an NSLog for [outlineView dataSource] and it returned as nil. I associated the dataSource to the outlineView originally by bindings in interfaceBuilder. I'm now assuming this is my problem. Why is my datasource being released? and how do I get it back if I can't prevent it being released?

Code:

refreshOutLineView:

rootNode = [[IFParentNode alloc] initWithTitle:@"Root" children:nil];
    NSInteger clientCounter;
    clientCounter = 0;
    NSFetchRequest *clientsFetchRequest = [[NSFetchRequest alloc] init];
    NSManagedObjectContext *clientsMoc = [clientsController managedObjectContext];
    NSLog(@"clientsMoc is : %@", clientsMoc);
    if(clientsMoc == nil) {
        NSLog(@"And, yes, clientsMoc is = nil");
        clientsMoc = [(Voiced_AppDelegate *)[[NSApplication sharedApplication] delegate] managedObjectContext]; 
        NSLog(@"After managedObjectContext: %@",  clientsMoc);
    }
    NSEntityDescription *clientsEntity = [NSEntityDescription entityForName:@"Clients" inManagedObjectContext:clientsMoc];
    //NSLog(@"clientsEntity, after the 'if nil' code is now: %@", clientsEntity);
    [clientsFetchRequest setEntity:clientsEntity];
    //sort
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"clientCompany" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [clientsFetchRequest setSortDescriptors:sortDescriptors];
    NSError *clientsFetchError = nil;
    clientsArray = [clientsMoc executeFetchRequest:clientsFetchRequest error:&clientsFetchError];
    [clientsFetchRequest release];
    //NSLog(@"clientsArray, after fetching is now: %@", clientsArray);

    NSInteger projectCounter;
    projectCounter = 0;
    NSFetchRequest *projectsFetchRequest = [[NSFetchRequest alloc] init];
    NSManagedObjectContext *projectsMoc= [projectsController managedObjectContext];
    if(projectsMoc == nil) {
        NSLog(@"And, yes, projectsMoc is = nil");
        projectsMoc = [(Voiced_AppDelegate *)[[NSApplication sharedApplication] delegate] managedObjectContext]; 
        NSLog(@"After managedObjectContext: %@",  projectsMoc);
    }
    NSEntityDescription *projectsEntity = [NSEntityDescription entityForName:@"Projects" inManagedObjectContext:projectsMoc];
    [projectsFetchRequest setEntity:projectsEntity];
    NSError *projectsFetchError = nil;
    projectsArray = [projectsMoc executeFetchRequest:projectsFetchRequest error:&projectsFetchError];
    [projectsFetchRequest release];
    //NSLog(@"projectsArray, after fetching is now: %@", projectsArray);

    for (NSString *s in clientsArray) {
        NSManagedObject *clientMo = [clientsArray objectAtIndex:clientCounter];  // assuming that array is not empty
        id clientValue = [clientMo valueForKey:@"clientCompany"];
        //NSLog(@"Company is %@", parentValue);

        IFParentNode *tempNode = [[IFParentNode alloc] initWithTitle:[NSString stringWithFormat:@"%@", clientValue] children:nil];

        clientCounter = clientCounter + 1;
        [rootNode addChild:tempNode];
        [tempNode release];
    }

    for (NSString *s in projectsArray) {
        NSInteger viewNodeIndex;
        viewNodeIndex = 0;
        NSManagedObject *projectMo = [projectsArray objectAtIndex:projectCounter];  // assuming that array is not empty
        id projectValue = [projectMo valueForKey:@"projectTitle"];
        id projectParent = [[projectMo valueForKey:@"projectParent"] valueForKey: @"clientCompany"];
        // find if theres an item with the projetParent name
        id nodeTitle = [[rootNode children] valueForKey:@"title"];
        for(NSString *companies in nodeTitle) {
            if([companies compare:projectParent] == NSOrderedSame) {
                //NSLog(@"Company is %@ and parent is %@ and id is: %d", companies, projectParent, viewNodeIndex);
                // then assign that node to be the tempnode.
                IFParentNode *tempNode = [rootNode.children objectAtIndex:viewNodeIndex];
                IFChildNode *subTempNode = [[IFChildNode alloc] initWithTitle:[NSString stringWithFormat:@"%@", projectValue]];
                [tempNode addChild:subTempNode];
                [subTempNode release];
                [tempNode release];
            } else {
                // do nothing.
            }
            viewNodeIndex = viewNodeIndex + 1;
        }
        projectCounter = projectCounter + 1;
    }
    [outlineView expandItem:nil expandChildren:YES];
    [outlineView reloadData];
}

outlineViewDataSource:

- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item {
    if([item isKindOfClass:[IFChildNode class]]) {
        return nil;
    }
    return (item == nil ? [rootNode childAtIndex:index] : [(IFParentNode *)item childAtIndex:index]);
}

- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item {
    return (item == nil || [item isKindOfClass:[IFParentNode class]]);
}

- (NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item {
    if([item isKindOfClass:[IFChildNode class]]) {
        return 0;
    }

    return (item == nil ? [rootNode numberOfChildren] : [(IFParentNode *)item numberOfChildren]);
}

- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item {
    if([item isKindOfClass:[IFChildNode class]]) {
        return ((IFChildNode *)item).title;
    }

    if([item isKindOfClass:[IFParentNode class]]) {
        return ((IFParentNode *)item).title;
    }

    return nil;
}

// Unessential methods for datasource

- (BOOL)outlineView:(NSOutlineView *)outlineView isGroupItem:(id)item {
    return (item == nil || [item isKindOfClass:[IFParentNode class]]);
}

- (BOOL)outlineView:(NSOutlineView *)outlineView shouldSelectItem:(id)item {
    return ([item isKindOfClass:[IFChildNode class]]);
}

/* - - - - - - - - - - - - - - - - - - - -
IfChild
 - - - - - - - - - - - - - - - - - - - - */

@implementation IFChildNode
@synthesize title;
- (id)initWithTitle:(NSString *)theTitle {
    if(self = [super init]) {
        self.title = theTitle;
    }

    return self;
}

- (void)dealloc {
    self.title = nil;
    [super dealloc];
}
@end

/* - - - - - - - - - - - - - - - - - - - -
IfParent
 - - - - - - - - - - - - - - - - - - - - */

@implementation IFParentNode
@synthesize title, children;
- (id)initWithTitle:(NSString *)theTitle children:(NSMutableArray *)theChildren {
    if(self = [super init]) {
        self.title = theTitle;
        self.children = (theChildren == nil ? [NSMutableArray new] : theChildren);
    }

    return self;
}

- (void)addChild:(id)theChild {
    [self.children addObject:theChild];
}

- (void)insertChild:(id)theChild atIndex:(NSUInteger)theIndex {
    [self.children insertObject:theChild atIndex:theIndex];
}

- (void)removeChild:(id)theChild {
    [self.children removeObject:theChild];
}

- (NSInteger)numberOfChildren {
    return [self.children count];
}

- (id)childAtIndex:(NSUInteger)theIndex {
    return [self.children objectAtIndex:theIndex];
}

- (void)dealloc {
    self.title = nil;
    self.children = nil;
    [super dealloc];
}

Answer 1

It looks to me like you are imposing a tree structure on the data in the controller instead of in the data model. You shouldn't have to fetch two entities into two arrays and then shoehorn them together to create your tree. The idea behind bindings is that controllers simply link the data model to the control and the control displays the object graph within the data model.

So, I think you need to back up and look at your data model again. I infer you need a data model something like this:

Client{
    name:string
    //... some other attributes
    projects<-->>Project.client
}

Project:
    name:string
    // ... some other attributes
    client<<-->Client.projects
}

You want an outline that shows Clients with their related Project objects as children.

If you use NSTreeController you would bind the tree controller to the entity Client with a child path of projects

If you use an Outline Data source, you would just fetch the Client objects sorted as you wish and then return them and their projects as needed.

The important thing here is that the outline or tree structure should be innate in the data model itself. If it is not, then you probably don't want the user looking at and thinking about the data in an outline form.

Remember as well that the data model is an entire layer of the Model-View-Controller design and is not just a dumb store of bits. It can and should contain all the logic necessary to represent the active data in the app. Arguably, the data model is the core of the app with the UI, networking or persistence tacked on as needed. Don't be afraid to put logic related to the data in the data model.

Answer 2

Most of the time, this means that you have inadvertently created two instances of your class. One is in your nib and hooked up to everything, while the other is either created in code or created elsewhere in a nib without any connections. An easy way to prove that this is happening is to log self both in awakeFromNib and some method that's seeing nil — you'll see different addresses for the two objects. You'll also find that outlineView itself is nil, since the outlet isn't hooked up to anything.