iOS 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);