Animating "sliding" in NSOutlineView

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 strat开发者_开发技巧egy for attempting this?

Animating this:

}} Folder 1

To expand and look like this:

}} Folder 1

}}}}} Item 1

}}}}} Item 2

}}}}} Item 3

Take a look at this project: TLAnimatingOutlineview

This is actually very simple, and you don’t need third-party libraries. Instead of calling the expandItem: / collapseItem: directly on your NSOutlineView instance, you pass them to the animator proxy object.

NSOutline *outlineView = ...;
id item = ...;
[[outlineView animator] collapseItem:item];

Also note that you can expand/collapse all the cells at once by passing a nil item.

Documentation: NSAnimatablePropertyContainer Protocol Reference