Returns the specified child of an item.
- macOS 10.10+
The index of the child item in the parent.
The parent item whose child item you want to retrieve.
The child item or
nil if the item could not be found.
You can call this method on an outline view with either a static or dynamic data source. For an outline view whose contents are dynamic, this method may call out to the
outline method of the associated data source object.