With NSTreeController, do I have to manually reload an NSOutlineView when changing the model array?

I have a tree-like model I'd like to show in an NSOutlineView using an NSTreeController. I was able to set up the bindings and everything works fine as long as I use the NSTreeController's insert and remove functions to change my model tree. If I try to insert or remove from the model tree directly, in some cases the NSOutlineView isn't updating. If I insert an object into an expanded group of objects, it works: But if I try to add the first object to a node, that had no children before, nothing happens. The disclosure triangle isn't appearing, so I can't expand it to see the new node. If I hover over that node with a new object, it is expanded and I can add the second child with no problems. But the triangle is still invisible: Finally if I close the parent of all these nodes and open them again (triggering a reload) the triangle suddenly appears: That's why I was wondering if I had to manually reload the NSOutlineView's rows to make the triangle visible, or if I'm messing up something? Thanks!! UPDATE: In my Node class I add a new child like this: ``` - (void)addChild:(MyNode *)child { [self willChangeValueForKey:@"childNodes"]; [children addObject:child]; [self didChangeValueForKey:@"childNodes"]; } ``` And I implemented these too (which I set in IB for my NSTreeController): ``` - (NSArray *)childNodes { return [NSArray arrayWithArray:children]; } - (NSInteger)countOfChildNodes { return [children count]; } - (BOOL)nodeIsLeaf { return [children count] < 1; } ``` I know that this (especially `childNodes`) aren't very optimized, but I'm only experimenting at the moment as in the final version my children will be stored in a C array. UPDATE 2: I also tried sending KVO notifications for the other 2 properties too, but that didn't help either. ``` - (void)addChild:(MyNode *)child { NSLog(@"%@", NSStringFromSelector(_cmd)); [self willChangeValueForKey:@"nodeIsLeaf"]; [self willChangeValueForKey:@"countOfChildNodes"]; [self willChangeValueForKey:@"childNodes"]; [children addObject:child]; [self didChangeValueForKey:@"childNodes"]; [self didChangeValueForKey:@"countOfChildNodes"]; [self didChangeValueForKey:@"nodeIsLeaf"]; } ```