This NSView subclass displays two subviews either stacked vertically, or side-by-side horizontally, separated by a divider that can be used to resize the subviews within the split view.

@interface NSSplitView : NSView
// Accessor Methods
- (void)setIsPaneSplitter:(BOOL)flag;
- (BOOL)isPaneSplitter;
- (void)setDelegate:(id)anObject;
- (id)delegate;
- (void)setVertical:(BOOL)flag;
// Instance Methods
- (float)dividerThickness;
- (BOOL)isVertical;
- (void)adjustSubviews;
- (void)drawDividerInRect:(NSRect)aRect;
- (BOOL)isSubviewCollapsed:(NSView *)subview;
// Methods Implemented by the Delegate
- (BOOL)splitView:(NSSplitView *)sender canCollapseSubview:(NSView *)subview;
- (float)splitView:(NSSplitView *)sender constrainMaxCoordinate:(float)proposedCoord ofSubviewAt:(int)offset;
- (float)splitView:(NSSplitView *)sender constrainMinCoordinate:(float)proposedCoord ofSubviewAt:(int)offset;
- (void)splitView:(NSSplitView *)sender resizeSubviewsWithOldSize:(NSSize)oldSize;
- (float)splitView:(NSSplitView *)splitView constrainSplitPosition:(float)proposedPosition ofSubviewAt:(int)index;
- (void)splitViewDidResizeSubviews:(NSNotification *)notification;
- (void)splitViewWillResizeSubviews:(NSNotification *)notification;
// Notifications
NSSplitViewDidResizeSubviewsNotification;
NSSplitViewWillResizeSubviewsNotification;