浅谈：深.浅拷贝与copy.strong
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：其它对象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;
測试：
#import "HSPerson.h"@interface HSPerson()@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);
能够看出copyWithZone又一次分配新的内存空间。则：
- (id)copyWithZone:(NSZone *)zone{ HSPerson *person = [[HSPerson allocWithZone:zone] init]; return person;// 有些人可能以下alloc,又一次初始化空间，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);
尽管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事实上就要被copy的那个对象，非常显然要自己赋值给新对象。所以这里能够控制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有啥差别？
事实上感觉不是必需有NSMutableCopying，由于压根就没可变的HSPerson，但假设该对象有其它行为，能够借用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@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，由于其内部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];} 如果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。假设有人用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;// 能够改变person.name的值，由于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。假设不希望被外界更改用copy。反之用strong