循環retain導緻記憶體洩露

問題描述

Dog.h

#import <Foundation/Foundation.h>
@class Person;
@interface Dog : NSObject
@property (nonatomic,retain) Person *owner;
@end
           

Person.h

#import <Foundation/Foundation.h>
@class Dog;
@interface Person : NSObject
@property (nonatomic,retain) Dog *dog;
@end
           

Dog的dealloc函數中有[Person dealloc]，Person的dealloc函數中有[Dog dealloc]

main.m

int main(int argc, const char * argv[]) {
    @autoreleasepool {

        Person *p = [Person new];  //1
        Dog *d = [Dog new];   //1
        NSLog(@"%lu , %lu",p.retainCount,d.retainCount);// 1 , 1
        //人有一條狗
        p.dog = d;    
        d.owner = p;  
        NSLog(@"%lu   %lu",p.retainCount,d.retainCount);// 2 , 2

        [p release];  //0
        NSLog(@"%lu   %lu",p.retainCount,d.retainCount);// 1 , 2
        [d release];  //
        NSLog(@"%lu   %lu",p.retainCount,d.retainCount);//1 , 1
    }
    return ;
}
           

p.dog = d;

d.owner = p;

這兩句執行完畢後是這樣子的：

[ p release] ;執行完畢後是這樣子的：

[d release]; 執行結束是這樣子，于是造成記憶體洩露

解決方法

讓一段使用@property的assign參數

例如在Dog.h中

@property (nonatomic,assign) Person *owner;
           

由于不是retain，在Dog的dealloc函數中不需要在寫[_owner dealloc]；

就可以解決問題。具體原因可以同上面的分析得出結論。