main.m文件
#import <Foundation/Foundation.h>
#import "Student.h"
#import "GoodStudent.h"
// copy语法的目的：改变副本的时候，不会影响到源对象
#pragma mark 字符串的拷贝（深拷贝）
// 深拷贝：内容拷贝，会产生新的对象。新对象计数器置为1，源对象计数器不变。
void stringMutableCopy() {
// string:1
NSString *string = [[NSString alloc] initWithFormat:@"age is %i", 10];
// 产生了一个新的对象，计数器为1。源对象的计数器不变。
// str:1
// string:1
NSMutableString *str = [string mutableCopy];
//NSLog(@"str:%zi", [str retainCount]);
//NSLog(@"string:%zi", [string retainCount]);
// str和string不是相同对象
// NSLog(@"%i", str == string);
[str appendString:@" abcd"];
NSLog(@"string:%@", string);
NSLog(@"str:%@", str);
// str:0
[str release];
// string:0
[string release];
}
#pragma mark 演示字符串的拷贝（浅拷贝）
// 只有一种情况是浅拷贝：不可变对象调用copy方法时
// 浅拷贝：指针拷贝，不会产生新的对象。源对象计数器+1。
void stringCopy() {
NSString *string = [[NSString alloc] initWithFormat:@"age is %i", 10];
NSLog(@"%zi", [string retainCount]);
// copy产生的是不可变副本，由于源对象本身就不可变，所以为了性能着想，copy会直接返回源对象本身
// 源对象计数器会+1
// 在浅拷贝情况下，copy其实就相当于retain
NSString *str = [string copy];
NSLog(@"%zi", [string retainCount]);
// NSLog(@"%i", str == string);
//NSString并不受引用计数器机制管理
//tring指向常量去,系统为了保护常量区的空间,把常量区的引用计数弄很大......如果用%d打印,会溢出,打印出来-1 此处%d(有黄色警报) == %iz(无警报哦)
[str release];
[string release];
}
#pragma mark 可变字符串的copy（深拷贝）
void mutableStringCopy() {
NSMutableString *string = [NSMutableString stringWithFormat:@"age is %i", 10];
// 会产生一个新对象，str计数器为1
NSString *str = [string copy];
[str release];
}
#pragma mark 可变字符串的MutableCopy（深拷贝）
void mutableStringMutableCopy() {
NSMutableString *string = [NSMutableString stringWithFormat:@"age is %i", 10];
// 会产生一个新对象，str计数器为1
NSMutableString *str = [string mutableCopy];
[str appendString:@"1234"];
NSLog(@"str:%@", str);
NSLog(@"string:%@", string);
[str release];
}
#pragma mark Student的name的copy
void studentNameCopy() {
Student *stu = [[[Student alloc] init] autorelease];
NSMutableString *string = [NSMutableString stringWithFormat:@"age is %i", 10];
stu.name = string;
[string appendString:@"abcd"];
NSLog(@"name=%@", stu.name);
NSLog(@"string=%@", string);
}
#pragma mark Student的copy
void studentCopy() {
Student *stu1 = [Student studentWithName:@"stu1"];
Student *stu2 = [stu1 copy];
stu2.name = @"stu2";
NSLog(@"stu1:%@", stu1);
NSLog(@"stu2:%@", stu2);
[stu2 release];
}
void goodStudentCopy() {
GoodStudent *stu1 = [GoodStudent goodStudentWithAge:10 name:@"good1"];
GoodStudent *stu2 = [stu1 copy];
stu2.name = @"good2";
stu2.age = 11;
NSLog(@"stu1:%@", stu1);
NSLog(@"stu2:%@", stu2);
}
int main(int argc, const char * argv[])
{
@autoreleasepool {
goodStudentCopy();
}
return 0;
}
Student.h文件
#import <Foundation/Foundation.h>
@interface Student : NSObject <NSCopying>
// copy代表set方法会release旧对象、copy新对象
// 修改外面的变量，并不会影响到内部的成员变量
// 建议：NSString一般用copy策略，其他对象一般用retain
@property (nonatomic, copy) NSString *name;
+ (id)studentWithName:(NSString *)name;
@end
Student.m文件
#import "Student.h"
@implementation Student
+ (id)studentWithName:(NSString *)name {
// 这里最好写[self class]
Student *stu = [[[[self class] alloc] init] autorelease];
stu.name = name;
return stu;
}
- (void)dealloc {
[_name release];
[super dealloc];
}
#pragma mark description方法内部不能打印self，不然会造成死循环
- (NSString *)description {
return [NSString stringWithFormat:@"[name=%@]", _name];
}
#pragma mark copying协议的方法
// 这里创建的副本对象不要求释放
- (id)copyWithZone:(NSZone *)zone {
Student *copy = [[[self class] allocWithZone:zone] init];
// 拷贝名字给副本对象
copy.name = self.name;
return copy;
}
@end
GoodStudent.h
#import "Student.h"
@interface GoodStudent : Student
@property (nonatomic, assign) int age;
+ (id)goodStudentWithAge:(int)age name:(NSString *)name;
@end
GoodStudent.m
#import "GoodStudent.h"
@implementation GoodStudent
+ (id)goodStudentWithAge:(int)age name:(NSString *)name {
GoodStudent *good = [GoodStudent studentWithName:name];
good.age = age;
return good;
}
- (NSString *)description {
return [NSString stringWithFormat:@"[name=%@, age=%i]", self.name, _age];
}
- (id)copyWithZone:(NSZone *)zone {
// 一定要调用父类的方法
GoodStudent *copy = [super copyWithZone:zone];
copy.age = self.age;
return copy;
}
@end