iOS--copy深浅拷贝and strong
2015-09-09 13:23 doudo 阅读(282) 评论(0) 编辑 收藏 举报多谢作者(汉斯哈哈哈),出自:http://www.jianshu.com/p/e6a7cdcc705d
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
copy.strong
说完深浅拷贝,理解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);
总结:用copy与strong取决于需求,如果不希望被外界更改用copy,反之用strong