UNTESTED but I already know this is still not quite right. See http://www.mikeash.com/pyblog/key-value-observing-done-right.html for what could go wrong. Should use MAKVONotificationCenter to do the KVO. In any case, this code is just to give a general id

gistfile1.m

// MyViewTickler.h

#import <Cocoa/Cocoa.h>

@interface MyViewTickler : NSObject
{
}

+ (id)sharedInstance;

/*! Call this in your view's init methods (init with and without coder). */
- (void)startObservingView:(NSView *)aView;

/*! Call this in your view's dealloc method. */
- (void)stopObservingView:(NSView *)aView;

@end



@interface NSView (ViewTickler)

/*!
 * Returns key paths that should trigger setNeedsDisplay:YES. Default returns
 * empty array, so you can safely call super in any NSView class.
 */
+ (NSArray *)keyPathsRequiringRedisplay;

@end

//----------------------------------------------

// MyViewTickler.m

#import "MyViewTickler.h"

@implementation MyViewTickler

+ (id)sharedInstance
{
    static MyViewTickler *s_sharedInstance = nil;
    
    if (s_sharedInstance == nil)
    {
        s_sharedInstance = [[self alloc] init];
    }
    
    return s_sharedInstance;
}

- (void)startObservingView:(NSView *)aView
{
    for (NSString *keyPath in [[aView class] keyPathsRequiringRedisplay])
    {
        [aView addObserver:self
                forKeyPath:keyPath
                   options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
                   context:NULL];
    }
}

- (void)stopObservingView:(NSView *)aView
{
    for (NSString *keyPath in [[aView class] keyPathsRequiringRedisplay])
    {
        [aView removeObserver:self forKeyPath:keyPath];
    }
}

- (void)observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context
{
    if ([object isKindOfClass:[NSView class]]
        && [[[object class] keyPathsRequiringRedisplay] containsObject:keyPath])
    {
        [(NSView *)object setNeedsDisplay:YES];
    }
    else
    {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

@end



@implementation NSView (ViewTickler)

+ (NSArray *)keyPathsRequiringRedisplay
{
    return [NSArray array];
}

@end