Objective-C Associative References (continued)

Objective-C Associative References (associated References)I am reading an article on KVC today, so I want to come up with a better understanding and a more practical understanding.

CAKeyframeAnimation *animation=[CAKeyframeAnimation animationWithKeyPath:@"position"];keyPosi.path=path;keyPosi.delegate=self;[label.layer addAnimation:animation forKey:@"position"];

- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag{}

[animation setValue:view forKey:@"xx"];

Then I modify the callback method:

- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag{    if (flag) {        UIView *vie=[anim valueForKey:@"xx"];        [vie removeFromSuperview];    }}

Is this correct?

*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<NSObject 0xf65f090> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key xx.'

Invoked by setValue:forKey: when it finds no property - ()setValue:()value forUndefinedKey:(NSString *DiscussionSubclasses can   method to handle the request  some other way. The  implementation raises an NSUndefinedKeyException.

And

#import <objc/runtime.h>@interface NSObject (KVC)- (id)valueForUndefinedKey:(NSString *)key;- (void)setValue:(id)value forUndefinedKey:(NSString *)key;@end@implementation NSObject(KVC)- (id)valueForUndefinedKey:(NSString *)key{    return objc_getAssociatedObject(self, key);}- (void)setValue:(id)value forUndefinedKey:(NSString *)key{    if ([value isKindOfClass:[NSString class]]) {        objc_setAssociatedObject(self, key, value, OBJC_ASSOCIATION_COPY_NONATOMIC);    }else{        objc_setAssociatedObject(self, key, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);    }}@end

This achieves the goal.