One Quickie
Responding to a scrollview scrolling (NSScrollView->General)
If you need to react to a scrollview being scrolled by the user, first tell the contentView (the NSClipView) to post notifications when its bounds changes, and then register to receive an NSViewBoundsDidChangeNotification:
[[scrollView contentView] setPostsBoundsChangedNotifications: YES];
NSNotificationCenter *center = [NSNotificationCenter defaultCenter] ;
[center addObserver: self
selector: @selector(boundsDidChangeNotification:)
name: NSViewBoundsDidChangeNotification
object: [scrollView contentView]];
...
- (void) boundsDidChangeNotification: (NSNotification *) notification
{
[self setNeedsDisplay: YES];
// or whatever work you need to do
} // boundsDidChangeNotification