Returns the child item at the specified index of a given item.
- macOS 10.0+
The outline view that sent the message.
The index of the child item from
An item in the data source.
The child item at
nil, returns the appropriate child item of the root object.
Children of a given parent
item are accessed sequentially. In order for the collapsed state of the outline view to remain consistent when it is reloaded you must always return the same object for a specified
outline method is called very frequently, so it must be efficient.