自定义类与NSCopying协议

#import <Foundation/Foundation.h>

/****************************************
 * Person类
 ****************************************/
// 要采用某个协议，需要在类的声明中列出该协议的名称，并用尖括号括起来
// 同时采用多个协议，则在协议的名称之间用逗号分割，如：<NSCopying, NSCoding>
// 可以按任意顺序列出多个协议
@interface Person : NSObject <NSCopying>

@property (nonatomic, copy, readwrite) NSString* name;

@end

@implementation Person

// copyWithZone:方法的返回类型为id，参数类型为NSZone
- (id)copyWithZone:(NSZone*)zone {
    
    // 通过使用[self class]，allocWithZone:消息将会被发送给正在接受copy消息的对象所属的类
    // 这个类可能是copyWithZone:消息所在类的子类，通过这种方式可以正确的创建想要的对象
    // 如果不使用[self class]，而使用具体的类名，可能导致创建得到的实例无法返回给类型正确的实例指针
    // allocWithZone:方法是一个类方法，其最后一行返回新创建的实例
    // zone是NSZone类的一个实例，指向一块可供分配的内存区域
    Person* personCopy = [[[self class] allocWithZone:zone] init];
    
    // 复制实例变量或属性
    [personCopy setName:[self name]];
    
    // 返回新创建的对象
    return personCopy;
}

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

- (void)dealloc {
    [[self name] release];
    [super dealloc];
}

@end

/****************************************
 * GoodPerson类
 ****************************************/
// 父类采用了某个协议，其子类也将遵守该协议，无需用不必要的代码说明
@interface GoodPerson : Person

@property (nonatomic, assign, readwrite) NSUInteger age;

@end

@implementation GoodPerson

- (id)copyWithZone:(NSZone*)zone {
    // 由于父类已经实现了copyWithZone:方法
    // 子类只需调用该方法，并完成属于自己需要负责的那部分复制操作即可
    GoodPerson* goodPersonCopy = [super copyWithZone:zone];
    
    [goodPersonCopy setAge:[self age]];
    
    return goodPersonCopy;
}

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

@end

/****************************************
 * main函数
 ****************************************/
int main(int argc, const char * argv[]) {
    Person* p1 = [[Person alloc] init];
    [p1 setName:@"AAA"];
    
    // 当向一个实例发送copy消息时，则该copy消息会被转换为调用copyWithZone:方法
    Person* p2 = [p1 copy];
    NSLog(@"Address(p1) = %p, retainCount(p1) = %lu", p1, [p1 retainCount]);
    NSLog(@"Address(p2) = %p, retainCount(p2) = %lu", p2, [p2 retainCount]);
    
    NSLog(@"p1%@", p1);
    NSLog(@"p2%@", p2);
    
    [p1 release];
    [p2 release];
    
    GoodPerson* gp1 = [[GoodPerson alloc] init];
    [gp1 setName:@"BBB"];
    [gp1 setAge:20];
    
    GoodPerson* gp2 = [gp1 copy];
    NSLog(@"Address(gp1) = %p, retainCount(gp1) = %lu", gp1, [gp1 retainCount]);
    NSLog(@"Address(gp2) = %p, retainCount(gp2) = %lu", gp2, [gp2 retainCount]);
    
    NSLog(@"gp1%@", gp1);
    NSLog(@"gp2%@", gp2);
    
    [gp1 release];
    [gp2 release];
    
    return 0;
}

Address(p1) = 0x1002021b0, retainCount(p1) = 1
Address(p2) = 0x1002021c0, retainCount(p2) = 1
p1[name = AAA]
p2[name = AAA]
Address(gp1) = 0x100205170, retainCount(gp1) = 1
Address(gp2) = 0x1002053d0, retainCount(gp2) = 1
gp1[name = BBB, age = 20]
gp2[name = BBB, age = 20]