问Objective-C - retainCount返回错误的值

EN

@class Person; 
@protocol PersonDelegate <NSObject> 
- (void)sendLetterForPerson:(Person *)p; 
@end 

@interface Person : NSObject 
@property (nonatomic, weak) id <PersonDelegate> delegate; 

- (void)writeLetterComplete; 
@end

@interface TestController ()<PersonDelegate> 
    @property (nonatomic, strong) Person *per; 
@end

_per = [[Person alloc] init];
_per.delegate = self;

NSLog(@"%lu",(unsigned long)_per.retainCount);
NSLog(@"%lu",(unsigned long)_per.delegate.retainCount);