"Learning the path to iOS: Objective-c" deep copy and shallow copy

The difference between shades of a copy:

Deep Copy Copy Content

Shallow copy copy Address

Note: When an object is str1 in a constant area

① copy NSString object to immutable string

        NSString *str1 = @ "Hello"; STR1--Constant Zone        NSLog (@ "%p", str1);//0x100002048        //copy        nsstring *str2 = [str1 copy];//0x100002048 str2--Constant area        NSLog (@ "%p", str2),//STR2 and str1 all point to constant area, same address, reference count is Infinity        NSLog (@ "str2 Retaincount =%lu", [str2 Retaincount]); <span style= "font-size:18px;" >//18446744073709551615</span>

② NSString objects for immutable strings Mutablecopy

        Mutablecopy, deep Copy, copy content, and copy it is a variable object        nsmutablestring *str3 = [str1 mutablecopy];        NSLog (@ "Str3 Retaincount =%lu", [Str3 Retaincount]);//1        [Str3 appendstring:@ "World"];//operations on copied objects        NSLog (@ "STR3 =%@", STR3);

Note: When the object str1 in the heap areawhen

        NSString *str1 = [NSString stringwithformat:@ "Frank"];        NSLog (@ "str1 =%p, Retaincount =%lu", str1, [str1 Retaincount]);//1

① copy NSString object to immutable string

        Copy, shallow copy, copy address, and add 1 to the reference count of the original object.        NSString *STR2 = [str1 copy];//str2 and str1 point to the same heap area space        NSLog (@ "str2 =%p, Retaincount =%lu", str2, [str2 Retaincount]); /2

② NSString objects for immutable strings mutablecopy

        Mutablecopy, deep Copy, copy content, the heap area opens up new space, and the copied object is mutable.        nsmutablestring *STR3 = [str1 mutablecopy];//str3 and str1 point to different objects        [str3 appendstring:@ "Lanou"];        NSLog (@ "STR3 =%p, Retaincount =%lu", STR3, [Str3 Retaincount]);//1

variable string (nsmutableString)
① to a mutable string nsmutablestring object copy

        The original object str1 in the heap area        nsmutablestring *str1 = [[Nsmutablestring alloc] initwithformat:@ "Frank"];        NSLog (@ "str1 =%p", str1),//0x10010b800        //copy A new space in the heap, copying the contents to a new space, but copying the immutable string object.        NSString *STR2 = [str1 copy];        NSLog (@ "str2 =%p, Retaincount =%lu", str2, [str2 Retaincount]);//1

② nsmutablestring object to a mutable string mutablecopy

        Mutablecopy A new space in the heap, copying the content to a new space, but copying a mutable string object.        nsmutablestring *STR3 = [str1 mutablecopy];        [Str3 appendstring:@ "Lanou"];        NSLog (@ "STR3 =%p, Retaincount =%lu", STR3, [Str3 Retaincount]);

Summary:

        /**         *  Summary: The copy is divided into mutable objects and immutable objects.            A shallow copy---  only copies the object address, does not copy the content, does not open up the new space.            Deep copy---  copy content, and the heap area opens up new space.            Immutable object: 1.copy is equivalent to Retin, the original object reference count plus 1, copy the address.                     2.mutableCopy Copy the new object, and the object is variable, open the content.            Mutable object: 1.copy Copies the new object, but the object is immutable and copies the contents.                     2.mutableCopy copies the new object, but the object is mutable and copies the contents.         */

③. For a custom object copy and Mutablecopy, you need to obey <nscopying, nsmutablecopying> protocol, for example:

1. Create Person.h

@interface person:nsobject <nscopying, nsmutablecopying> @property (nonatomic, copy) NSString *name; Name @property (nonatomic, copy) NSString *gender; Sex @property (nonatomic) Nsinteger age;//age @end

2.person.m File ComplianceProtocol

@implementation person-(ID) Copywithzone: (Nszone *) zone{person    *newperson = [[self class] allocwithzone:zone] INIT];    Newperson.name = [self.name copy];    Newperson.gender = [Self.gender copy];    Newperson.age = Self.age;    return Newperson;} -(ID) Mutablecopywithzone: (Nszone *) zone{person    *newperson = [[self class] allocwithzone:zone] init];    Newperson.name = [Self.name mutablecopy];    Newperson.gender = [Self.gender mutablecopy];    Newperson.age = Self.age;    return Newperson;} -(void) dealloc{    self.name = nil;    Self.gender = nil;    [Super Dealloc];} @end

implementation, analysis of deep-and-shallow copies

       Person copy with mutablecopy nsstring *name = [NSString stringwithformat:@ "Wang"];                NSString *gender = [NSString stringwithformat:@ "man"];        Person *per = [[Person alloc] init];        Per.name = name;        Per.gender = gender; NSLog (@ "per =%p", per);//0x10010b980//per name = 0x100100560, gender = 0X100104AC0 (pre-copy address)  nslo                G (@ "per name =%p, gender =%p", Per.name, Per.gender);                Person *copyperson = [per copy];                                      Copyperson = 0x100500a90, Retaincount = 1 (post-copy address)  nslog (@ "Copyperson =%p, Retaincount =%lu",        Copyperson, [Copyperson Retaincount]); (Copy the content address unchanged, copy the address in the past)//copyperson name = 0x100100560, gender = 0x100104ac0 NSLog (@ "Copyperson name =%p,            Gender =%p ",  copyperson.name, Copyperson.gender);               Person *mutacopyperson = [per Mutablecopy]; CopymutacopypErsonperson = 0X100401D50, Retaincount = 1  nslog (@ "Copymutacopypersonperson =%p, Retaincount         =%lu ", Mutacopyperson, [Mutacopyperson Retaincount]); (mutablecopy) address is different, that is, the copy is the content//mutacopyperson name = 0x100401450, gender = 0x1004014e0 NSLog (@ "Mutacopyperson         Name =%p, gender =%p ",  mutacopyperson.name, Mutacopyperson.gender);

"Learning the path to iOS: Objective-c" deep copy and shallow copy