NSOutlineView ObjectValueForTableColumn extra call triggers BAD ACCESS - objective-c

Question

When testing I have found that outlineView:objectValueForTableColumn:byItem: is being called one extra time after the last visible row is populated resulting in a EXC_BAD_ACCESS error.
So if my display is showing 10 rows, after row 9 is populated objectValueForTableColumn is called again (without outlineView:child:ofItem: and outlineView:isItemExpandable: being called). The extra call always happens after the last visible row is populated.
Here is my code for the outlineView. There are 2 columns and 114 records in my test data set.
// (1)
- (NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item {
if (!item) {
NSInteger parentCount = [[Parent countParents:self.dataSetID usingManagedObjectContext:self.context] integerValue];
return parentCount;
}
Parent *thisParent = item;
NSInteger childCount = [[thisParent.child allObjects] count];
return childCount;
}
// (2)
- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item {
NSArray *parentArray = [Parent parentData:self.dataSetID usingManagedObjectContext:self.context];
Parent *thisParent = [parentArray objectAtIndex:index];
if (!item) {
return thisParent;
}
NSArray *children = [NSArray arrayWithObject:[thisParent.child allObjects]];
Child *thisChild = [children objectAtIndex:index];
return thisChild;
}
// (3)
- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item {
if ([item isKindOfClass:[Parent class]]) {
Parent *thisParent = item;
if ([[thisParent.child allObjects] count] > 0) {
return YES;
}
}
return NO;
}
// (4)
- (id)outlineView:(NSOutlineView *)outlineView objectValueForTableColumn:(NSTableColumn *)tableColumn byItem:(id)item {
if (!item) {
return nil;
}
if ([tableColumn.identifier isEqualToString:#"column1"]) {
if ([item isKindOfClass:[Parent class]]) {
Parent *thisParent = item;
return thisParent.name;
}
Child *thisChild = item;
return thisChild.name;
}
// This is column2
if ([item isKindOfClass:[Parent class]]) {
Parent *thisParent = item;
return thisParent.age;
}
Child *thisChild = item;
return thisChild.age;
}
I've noticed that the methods are called in the order: 1,2,3,4,4,2,3,4,4... to populate the two column NSOutlineView. For the last visible row the order is: 2,3,4,4,4 with the last call to method #4 (outlineView:objectValueForTableColumn:byItem:) causing the exception.
I can not tell you the values being passed to the method because it breaks on the call. Even if the first thing in the method is a log statement it doesn't get executed.
So I'm stumped. Any ideas why this is breaking? Did I goof on the implementation?

Answer 1

In - (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item
you do not appear to use item - you should be returning the child item at the specified index of a given item.
Incidentally your code is inefficient - you should be trying to make these run as fast as possible.
You probably want:-
- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item {
if (item == nil)
return [[Parent parentData:self.dataSetID usingManagedObjectContext:self.context] objectAtIndex:index];
return [[NSArray arrayWithObject:[item.child allObjects]] objectAtIndex:index];
}