自定义类与NSCopying协议
代码:
#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; }
输出:
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]
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