OC之Copy语法

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• 概念
• 内存管理
• NSString的copy实例
• 对象的copy实例

一、概念

目的：在改变原有对象的时候，不会改变新对象的值

1. Copy：实现NSCopying协议，创建的是一个不可变副本
2. MutableCopy：实现NSMutableCopying协议，创建的是一个可变副本

二、内存管理

1. 深拷贝：产生新的对象，所以源对象计数器不变>>>对象拷贝
2. 浅拷贝：不产生新对象，所以源对象计数器加一>>>指针拷贝（因为对象本身不可以变，所有没有必要再创建一个对象）

三、NSString的copy实例

//
//  main.m
//  Copy语法
//
//  Created by apple on 14-3-28.
//  Copyright (c) 2014年 apple. All rights reserved.
//

#import <Foundation/Foundation.h>

void test1()
{
    NSString *str = [NSString stringWithFormat:@"age is %i", 10];
    NSString *str1 = [str copy];
    
    NSLog(@"%i", str == str1);
    
    NSString *str2 = [str mutableCopy];
    
    NSLog(@"%i", str2 == str);
}

void test2()
{
    NSMutableString *str = [NSMutableString stringWithFormat:@"age is %i", 11];
    
    NSString *str1 = [str copy];
    NSMutableString *str2 = [str mutableCopy];
    
    [str appendFormat:@"1"];
    
    NSLog(@"%i", str == str2);
    NSLog(@"%i", str == str1);
    NSLog(@"%@", str);
    NSLog(@"%@", str1);
}

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

    @autoreleasepool {
        
        test2();
        
    }
    return 0;
}

四、对象拷贝的实例

对象的拷贝，主要注意点

1.  必须实现NSCopying协议
2. 需要重写- (id)copyWithZone:(NSZone *)zone方法
3. 代码中 self class的引用

1⃣️GoodStudent.h

//
//  GoodStudent.h
//  Student的Copy用法
//
//  Created by apple on 14-3-28.
//  Copyright (c) 2014年 apple. All rights reserved.
//

#import "Student.h"

@interface GoodStudent : Student

@property (nonatomic, assign) int age;

+(id)goodStudentWithName:(NSString *)name withAge:(int)age;

@end

2⃣️GoodStudent.m

//
//  GoodStudent.m
//  Student的Copy用法
//
//  Created by apple on 14-3-28.
//  Copyright (c) 2014年 apple. All rights reserved.
//

#import "GoodStudent.h"

@implementation GoodStudent

+(id)goodStudentWithName:(NSString *)name withAge:(int)age
{
    GoodStudent *stu = [super studentWithName:name];
    stu.age = age;
    
    return stu;
}

-(id)copyWithZone:(NSZone *)zone
{
    GoodStudent *copy = [super copyWithZone:zone];
    copy.age = self.age;
    
    return copy;
}

-(NSString *)description
{
    return [NSString stringWithFormat:@"%@-%i", self.name, self.age];
}

@end

3⃣️Student.h

//
//  Student.h
//  Student的Copy用法
//
//  Created by apple on 14-3-28.
//  Copyright (c) 2014年 apple. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface Student : NSObject <NSCopying>

@property (nonatomic, copy) NSString *name;

+(id)studentWithName:(NSString*)name;

@end

4⃣️Student.m

//
//  Student.m
//  Student的Copy用法
//
//  Created by apple on 14-3-28.
//  Copyright (c) 2014年 apple. All rights reserved.
//

#import "Student.h"

@implementation Student
+(id)studentWithName:(NSString *)name
{
    Student *stu = [[[[self class] alloc] init] autorelease];
    stu.name = name;
    
    return stu;
}

- (id)copyWithZone:(NSZone *)zone
{
    Student *copy = [[self class] allocWithZone:zone];
    
    copy.name = self.name;
    
    return copy;
}

-(NSString *)description
{
    return [NSString stringWithFormat:@"%@", self.name];
}

-(void)dealloc
{
    [_name release];
    [super dealloc];
}
@end

main.m

//
//  main.m
//  Student的Copy用法
//
//  Created by apple on 14-3-28.
//  Copyright (c) 2014年 apple. All rights reserved.
//

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

void test1()
{
    Student *stu = [Student studentWithName:@"name1"];
    Student *stu1 = [stu copy];
    
    NSLog(@"%@", stu);
    NSLog(@"%@", stu1);
}

void test2()
{
    GoodStudent *stu1 = [GoodStudent goodStudentWithName:@"name1" withAge:10];
    
    GoodStudent *stu2 = [stu1 copy];
    
    NSLog(@"%@", stu1);
    NSLog(@"%@", stu2);
    
}

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

    @autoreleasepool {
        
        test2();
        
    }
    return 0;
}