20-内存管理03(copy/mutableCopy/autor

一、MRC内存管理

• assign:修饰基本数据类型，setter方法就直接赋值，不会先释放旧对象再进行赋值。
• retain:修饰OC对象，setter方法需要先释放旧对象再赋值新对象。

二、Copy、mutableCopy

拷贝的目的：产生一个副本对象，跟源对象互不影响。

• Copy:不可变拷贝，产生不可变副本。

• mutableCopy:可变拷贝，产生可变副本。

• 深拷贝：内容拷贝，产生新的对象。

• 浅拷贝：指针拷贝，不会产生新的对象。
  在MRC环境下使用copy、mutableCopy会进行retain操作，所以要进行release操作。
  mutalbeCopy:只针对系统Foundation框架下的类进行的操作，属性只要copy操作，因为属性是不确定的类，要保持通用性。

• 1.系统类的拷贝
  

  

• 2.自定义类的拷贝

  • 1.自定义的类要遵守NSCopying协议
  • *2.实现协议中的- (id)copyWithZone:(nullable NSZone )zone;方法

---------------------------------------------------MJPerson.h----------------------------------------------
#import <Foundation/Foundation.h>

@interface MJPerson : NSObject <NSCopying>
@property (assign, nonatomic) int age;
@property (assign, nonatomic) double weight;
@end
---------------------------------------------------MJPerson.m----------------------------------------------
#import "MJPerson.h"

@implementation MJPerson

- (id)copyWithZone:(NSZone *)zone
{
    MJPerson *person = [[MJPerson allocWithZone:zone] init];
    person.age = self.age;
//    person.weight = self.weight;
    return person;
}

- (NSString *)description
{
    return [NSString stringWithFormat:@"age = %d, weight = %f", self.age, self.weight];
}

@end
--------------------------------------------------main.m-----------------------------------------------
#import <Foundation/Foundation.h>
#import "MJPerson.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MJPerson *p1 = [[MJPerson alloc] init];
        p1.age = 20;
        p1.weight = 50;

        MJPerson *p2 = [p1 copy];
        p2.age = 30;

        NSLog(@"%@", p1);
        NSLog(@"%@", p2);

        [p2 release];
        [p1 release];
    }
    return 0;
}

三、引用计数的存储

objc源码分析

四、weak指针的原理

objc源码分析

五、autorelease原理

#import <Foundation/Foundation.h>
#import "MJPerson.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
//        atautoreleasepoolobj = objc_autoreleasePoolPush();
        
        for (int i = 0; i < 1000; i++) {
            MJPerson *person = [[[MJPerson alloc] init] autorelease];
        } // 8000个字节
        
//        objc_autoreleasePoolPop(atautoreleasepoolobj);
    }
    return 0;
}

/*
 
 struct __AtAutoreleasePool {
    __AtAutoreleasePool() { // 构造函数，在创建结构体的时候调用
        atautoreleasepoolobj = objc_autoreleasePoolPush();
    }
 
    ~__AtAutoreleasePool() { // 析构函数，在结构体销毁的时候调用
        objc_autoreleasePoolPop(atautoreleasepoolobj);
    }
 
    void * atautoreleasepoolobj;
 };
 
 {
    __AtAutoreleasePool __autoreleasepool;
    MJPerson *person = ((MJPerson *(*)(id, SEL))(void *)objc_msgSend)((id)((MJPerson *(*)(id, SEL))(void *)objc_msgSend)((id)((MJPerson *(*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("MJPerson"), sel_registerName("alloc")), sel_registerName("init")), sel_registerName("autorelease"));
 }
 
 
    atautoreleasepoolobj = objc_autoreleasePoolPush();
 
    MJPerson *person = [[[MJPerson alloc] init] autorelease];
 
    objc_autoreleasePoolPop(atautoreleasepoolobj);
 */

六、RunLoop与autorelease

#import "ViewController.h"
#import "MJPerson.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 这个Person什么时候调用release，是由RunLoop来控制的
    // 它可能是在某次RunLoop循环中，RunLoop休眠之前调用了release
//    MJPerson *person = [[[MJPerson alloc] init] autorelease];
    
    MJPerson *person = [[MJPerson alloc] init];
    
    NSLog(@"%s", __func__);
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    
    NSLog(@"%s", __func__);
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    
    NSLog(@"%s", __func__);
}

/*
 typedef CF_OPTIONS(CFOptionFlags, CFRunLoopActivity) {
 kCFRunLoopEntry = (1UL << 0),  1
 kCFRunLoopBeforeTimers = (1UL << 1), 2
 kCFRunLoopBeforeSources = (1UL << 2), 4
 kCFRunLoopBeforeWaiting = (1UL << 5), 32
 kCFRunLoopAfterWaiting = (1UL << 6), 64
 kCFRunLoopExit = (1UL << 7), 128
 kCFRunLoopAllActivities = 0x0FFFFFFFU
 };
 */

/*
 kCFRunLoopEntry  push
 
 <CFRunLoopObserver 0x60000013f220 [0x1031c8c80]>{valid = Yes, activities = 0x1, repeats = Yes, order = -2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x103376df2), context = <CFArray 0x60000025aa00 [0x1031c8c80]>{type = mutable-small, count = 1, values = (\n\t0 : <0x7fd0bf802048>\n)}}
 
 
 kCFRunLoopBeforeWaiting | kCFRunLoopExit
 kCFRunLoopBeforeWaiting: pop、push
 kCFRunLoopExit pop
 
 <CFRunLoopObserver 0x60000013f0e0 [0x1031c8c80]>{valid = Yes, activities = 0xa0, repeats = Yes, order = 2147483647, callout = _wrapRunLoopWithAutoreleasePoolHandler (0x103376df2), context = <CFArray 0x60000025aa00 [0x1031c8c80]>{type = mutable-small, count = 1, values = (\n\t0 : <0x7fd0bf802048>\n)}}
 */

@end

`