Allows the delegate to determine whether the user can collapse and uncollapse
- macOS 10.0+
The split view that sent the message.
The subview to collapse.
subview should collapse when the user drags a divider beyond the halfway mark between its minimum size and its edge, otherwise
subview uncollapses when the user drags the divider back beyond the halfway mark between its minimum size and its edge.
To specify the minimum size, define the methods
split. A subview can collapse only if you also define
A collapsed subview is hidden but retained by the split view object, with the same size it had before it was collapsed.
If the delegate does not implement this method the subviews can’t be collapsed.