weak associate

NSObject+ZDWeakAssociate

@implementation NSObject (ZDWeakAssociate)

- (void)zd_setWeakAssociateValue:(id)value forKey:(void *)key {
    __weak id weakValue = value;
    objc_setAssociatedObject(self, key, ^{
        return weakValue;
    }, OBJC_ASSOCIATION_COPY);
}

- (id)zd_getWeakAssociateValueForKey:(void *)key {
    id(^tempBlock)() = objc_getAssociatedObject(self, key);
    if (tempBlock) {
        return tempBlock();
    }
    return nil;
}

@end