Animating "sliding" in NSOutlineView

Question

I've done a fair amount of Googling, but still haven't find any proper solution for animating the expansion of NSOutlineView. I'm trying to mimic a "sliding" animation when expanding/collapsing rows. Anyone know a good strategy for attempting this?

Animating this:

}} Folder 1

To expand and look like this:

}} Folder 1

}}}}} Item 1

}}}}} Item 2

}}}}} Item 3

Answer 1

Take a look at this project: TLAnimatingOutlineview