深.浅拷贝
- copy/mutableCopy NSString
NSString *string = @"汉斯哈哈哈";
// 没有产生新对象
NSString *copyString = [string copy];
// 产生新对象
NSMutableString *mutableCopyString = [string mutableCopy];
NSLog(@"string = %p copyString = %p mutableCopyString = %p", string, copyString, mutableCopyString);
- copy/mutableCopy NSMutableString
NSMutableString *string = [NSMutableString stringWithString:@"汉斯哈哈哈"];
// 产生新对象
NSString *copyString = [string copy];
// 产生新对象
NSMutableString *mutableCopyString = [string mutableCopy];
NSLog(@"string = %p copyString = %p mutableCopyString = %p", string, copyString, mutableCopyString);
结论：
注意：其他对象NSArray、NSMutableArray 、NSDictionary、NSMutableDictionary一样适用
- copy NSObject
HSPerson *p = [[HSPerson alloc] init];
p.age = 20;
p.height = 170.0;
HSPerson *copyP = [p copy]; // 这里崩溃
崩溃：
看崩溃信息HSPerson应该先实现：
- (id)copyWithZone:(NSZone *)zone;
测试：
#import "HSPerson.h"
@interface HSPerson()<NSCopying>
@end
@implementation HSPerson
- (id)copyWithZone:(NSZone *)zone
{
return @"汉斯哈哈哈";
}
@end
HSPerson *p = [[HSPerson alloc] init];
p.age = 20;
p.height = 170.0;
HSPerson *copyP = [p copy];
NSLog(@"copyP: %@", copyP);
可以看出copyWithZone重新分配新的内存空间，则：
- (id)copyWithZone:(NSZone *)zone
{
HSPerson *person = [[HSPerson allocWithZone:zone] init];
return person;
// 有些人可能下面alloc,重新初始化空间，但这方法已给你分配了zone，自己就无需再次alloc内存空间了
// HSPerson *person = [[HSPerson alloc] init];
}
HSPerson *p = [[HSPerson alloc] init];
p.age = 20;
p.height = 170.0;
HSPerson *copyP = [p copy];
NSLog(@"p = %p copyP = %p", p, copyP);
NSLog(@"age = %d height = %f", copyP.age, copyP.height);
虽然copy了份新的对象，然而age,height值并未copy，那么：
- (id)copyWithZone:(NSZone *)zone
{
HSPerson *person = [[HSPerson allocWithZone:zone] init];
person.age = self.age;
person.height = self.height;
// 这里self其实就要被copy的那个对象，很显然要自己赋值给新对象，所以这里可以控制copy的属性
return person;
}
这时你会想，有NSMutableCopying？没错，是有这货：
- (id)mutableCopyWithZone:(NSZone *)zone
{
HSPerson *person = [[HSPerson allocWithZone:zone] init];
person.age = self.age;
person.height = self.height;
return person;
}
NSCopying、NSMutableCopying有啥区别？
其实感觉没必要有NSMutableCopying，因为压根就没可变的HSPerson，但如果该对象有其他行为，可以借用NSMutableCopying实现，哈哈哈
property里的copy、strong区别
说完深浅拷贝，理解property里的copy、strong就轻松多了！
- copy
#import <Foundation/Foundation.h>
@interface HSPerson : NSObject
@property (nonatomic, copy) NSString *name;
@end
NSMutableString *string = [NSMutableString stringWithFormat:@"汉斯哈哈哈"];
HSPerson *person = [[HSPerson alloc] init];
person.name = string;
// 不能改变person.name的值，因为其内部copy新的对象
[string appendString:@" hans"];
NSLog(@"name = %@", person.name);
property copy 实际上就对name干了这个：
- (void)setName:(NSString *)name
{
_name = [name copy];
}
假设name为NSMutableString，会发生什么事？
@property (nonatomic, copy) NSMutableString *name;
这样会挨骂哦，实际上内部还是：
- (void)setName:(NSMutableString *)name
{
_name = [name copy];
}
copy出来的仍然是不可变字符！如果有人用NSMutableString的方法，就会崩溃:
- strong
@property (nonatomic, strong) NSString *name;
NSMutableString *string = [NSMutableString stringWithFormat:@"汉斯哈哈哈"];
HSPerson *person = [[HSPerson alloc] init];
person.name = string;
// 可以改变person.name的值，因为其内部没有生成新的对象
[string appendString:@" hans"];
NSLog(@"name = %@", person.name);
文章同步到微信公众号：hans_iOS 有疑问可以在公众号里直接发
