Invoked to allow a delegate to determine if a subview should collapse in response to a double click.
- macOS 10.5+
The split view that sent the message.
The subview to collapse.
The index of the divider.
true if the subview should collapse,
If implemented, the delegate will receive this message once for the subview before a divider when the user double-clicks on that divider, and again for the subview after the divider, but only if the delegate returned
true when sent
split for the subview in question. When the delegate indicates that both subviews should be collapsed NSSplitView's behavior is undefined.