Objective-C - ARC(Automatic Reference Counting)自动引用技术详解

ARC特点与判断准则

/*
 ARC的判断准则：只要没有强指针指向对象，就会释放对象

 1.ARC特点
 1> 不允许调用release、retain、retainCount
 2> 允许重写dealloc，但是不允许调用[super dealloc]
 3> @property的参数
  * strong ：成员变量是强指针（适用于OC对象类型）
  * weak ：成员变量是弱指针（适用于OC对象类型）
  * assign : 适用于非OC对象类型
 4> 以前的retain改为用strong

 指针分2种：
 1> 强指针：默认情况下，所有的指针都是强指针 __strong
 2> 弱指针：__weak

 */

int main()
{
    Dog *d = [[Dog alloc] init];

    Person *p = [[Person alloc] init];
    p.dog = d;

    d = nil;

    NSLog(@"%@", p.dog);

    return 0;
}

void test()
{
    // 错误写法（没有意义的写法）
    __weak Person *p = [[Person alloc] init];

    NSLog(@"%@", p);

    NSLog(@"------------");
}

@class Dog;

@interface Person : NSObject

@property (nonatomic, strong) Dog *dog;

@property (nonatomic, strong) NSString *name;

@property (nonatomic, assign) int age;

@end

@implementation Person

- (void)dealloc
{
    NSLog(@"Person is dealloc");

    // [super dealloc];
}

@end

@interface Dog : NSObject

@end

@implementation Dog
- (void)dealloc
{
    NSLog(@"Dog is dealloc");
}
@end

ARC循环引用问题

/**
 *   当两端循环引用的时候，解决方案：
 1> ARC
 1端用strong，另1端用weak

 2> 非ARC
 1端用retain，另1端用assign
 */
int main()
{
    Person *p = [[Person alloc] init];

    Dog *d = [[Dog alloc] init];
    p.dog = d;
    d.person = p;

    return 0;
}

@class Dog;

@interface Person : NSObject

@property (nonatomic, strong) Dog *dog;

@end

@implementation Person

- (void)dealloc
{
    NSLog(@"Person--dealloc");
}

@end

@class Person;

@interface Dog : NSObject

@property (nonatomic, weak) Person *person;

@end

@implementation Dog
- (void)dealloc
{
    NSLog(@"Dog--dealloc");
}
@end