关联引用

static char overviewKey;
NSArray *array = [[NSArray alloc] initWithObjects:@"One", @"Two", @"Three", nil];
// For the purposes of illustration, use initWithFormat: to ensure the string can be deallocated
NSString *overview = [[NSString alloc] initWithFormat:@"%@", @"First three numbers"];
objc_setAssociatedObject(array, &overviewKey, overview, OBJC_ASSOCIATION_RETAIN);
[overview release];
// (1) overview valid
[array release];
// (2) overview invalid

#import
#import
int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    static char overviewKey;
    NSArray *array = [[NSArray alloc] initWithObjects:@"One", @"Two", @"Three", nil];
    // For the purposes of illustration, use initWithFormat: to ensure we get a
    // deallocatable string
    NSString *overview = [[NSString alloc] initWithFormat:@"%@", @"First three numbers"];
    objc_setAssociatedObject(array, &overviewKey, overview, OBJC_ASSOCIATION_RETAIN);
    [overview release];
    NSString *associatedObject = (NSString *)objc_getAssociatedObject(array, &overviewKey);
    NLog(@"associatedObject: %@", associatedObject);
    objc_setAssociatedObject(array, &overviewKey, nil, OBJC_ASSOCIATION_ASSIGN);
    [array release];
    [pool drain];
    return 0;
}