iOS底层学习-day-26

前言-OC-内存管理篇

我是一名iOS开发者， iOS底层 菜鸟的进阶之路30天。

UITextField中的placeholder都是不可变的

@property(nullable, nonatomic,copy)   NSString               *placeholder; 

//都是分可变和不可变的
NSArray, NSMutableArray;
NSDictionary, NSMutableDictionary;
NSString, NSMutableString;
NSData, NSMutableData;
NSSet, NSMutableSet;

类进行copy

• 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

• 使用

MJPerson *p1 = [[MJPerson alloc] init];
p1.age = 20;
p1.weight = 50;

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

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

ARC

    // ARC是LLVM编译器和Runtime系统相互协作的一个结果
    
    __strong MJPerson *person1;
    __weak MJPerson *person2;//指向的值会自动清空
    __unsafe_unretained MJPerson *person3;//指向的值不会自动清空
    
    
    NSLog(@"111");
    
    {
        MJPerson *person = [[MJPerson alloc] init];
        
        person3 = person;
    }
    
    NSLog(@"222 - %@", person3);

autorelease

• oc 的 autorelease 在c++中的结果

 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);