private void SetupLeadingSplitViewItem() { NSSplitViewItem splitViewItem = NSSplitViewItem.CreateContentList(LeadingContentListViewController); splitViewItem.CanCollapse = true; splitViewItem.MaximumThickness = 400; AddSplitViewItem(splitViewItem); Disposables.Add(splitViewItem.AddObserver(KeyPath.NSSplitViewItem.Collapsed.String(), New, change => { NSDictionary userInfo = new NSDictionary ( ToggleCollapsed.UserInfoKey.IsCollapsed.String(), change.NewValue, ToggleCollapsed.UserInfoKey.SegmentIndex.String(), 0 ); NotificationCenter.PostNotificationName(ToggleCollapsed.Name, null, userInfo); })); }