iOS - 如何深拷贝Array内元素、自定义对象、及自定义对象

作者: 码代码的小马 | 来源:发表于2021-05-09 10:52 被阅读0次

由上篇我们知道:

copy： 对NSArray是浅拷贝，NSMutableArray是深拷贝

mutableCopy： 始终是深拷贝

无论深浅拷贝，集合对象内元素都是浅拷贝

本篇主要探索

实现NSArray内元素的拷贝

通过本文你将知道

深拷贝NSArray

深拷贝NSArray内元素Person

深拷贝NSArray内元素Person的属性nickname

本文代码较多，建议一步步耐心跟着代码排查，会有不少收货

探索过程

1. 系统Api

我们发现系统系统了方法- (instancetype)initWithArray:(NSArray<ObjectType> *)array copyItems:(BOOL)flag
其中copyItems:(BOOL)flag表示是否拷贝元素，我们先代码测试一下

    NSString *str1 = @"hello world";
    NSMutableString *str2 = [NSMutableString stringWithString:@"hello world"];
    NSArray *array1 = [NSArray arrayWithObjects: str1, str2, nil];
    NSMutableArray *array2 = [[NSMutableArray alloc] initWithArray:array1 copyItems:true];

    NSLog(@"\n array1 = %p class = %@ \n", array1, [array1 class]);
    NSLog(@"\n array2 = %p class = %@ \n", array2, [array2 class]);

    NSLog(@"\n\n======== 元素是String ======== ");
    NSLog(@"\n obj0 = %p class = %@ \n", array1[0], [array1[0] class]);
    NSLog(@"\n obj0 = %p class = %@ \n", array2[0], [array2[0] class]);

    NSLog(@"\n\n======== 元素是mutableString ========");
    NSLog(@"\n obj0 = %p class = %@ \n", array1[1], [array1[1] class]);
    NSLog(@"\n obj0 = %p class = %@ \n", array2[1], [array2[1] class]);

查看输出(为了下文对比，我对输出做了line标记)

2021-05-09 10:59:16.343163+0800 AlgorithmDemo[9904:51756] 
 array1 = 0x100607650 class = __NSArrayI  (line1)
 array2 = 0x1006074a0 class = __NSArrayM (line2)

======== 元素是String ======== 
 obj0 = 0x100008220 class = __NSCFConstantString (line3)
 obj0 = 0x100008220 class = __NSCFConstantString (line4)

======== 元素是mutableString ========
 obj0 = 0x100606330 class = __NSCFString (line5)
 obj0 = 0x100605430 class = __NSCFString (line6)

根据输出我们对得出系统initWithArray : copyItems :方法如下结论

~~该方法对NSArray对象是深拷贝~~ (严格意义来说此处不能称为拷贝，是生成新对象) （line1 line2）
当数组内元素为不可变对象时，该方法对元素执行浅拷贝(line3 line4)
当数组内元素为可变对象时，该方法对元素执行深拷贝(line4 line5)

由此我们知道，当我们想深拷贝NSArray及其内部的元素时，用系统方法- (instancetype)initWithArray:(NSArray<ObjectType> *)array copyItems:(BOOL)flag是不行的

2. 归档

如果我们对Array执行归档再解档，结果会是什么样的呢，我们代码测试一下

    NSString *str1 = @"hello world";
    NSMutableString *str2 = [NSMutableString stringWithString:@"hello world"];
    NSArray *array1 = [NSArray arrayWithObjects: str1, str2, nil];
    NSMutableArray *array2 = [[NSMutableArray alloc] initWithArray:array1 copyItems:true];
    
    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:array1];
    NSMutableArray *array3 = [NSKeyedUnarchiver unarchiveObjectWithData:data];
    
    NSLog(@"\n array1 = %p class = %@ \n", array1, [array1 class]);
    NSLog(@"\n array2 = %p class = %@ \n", array2, [array2 class]);
    NSLog(@"\n array3 = %p class = %@ \n", array3, [array3 class]);
    
    NSLog(@"\n\n======== 元素是String ======== ");
    NSLog(@"\n obj0 = %p class = %@ \n", array1[0], [array1[0] class]);
    NSLog(@"\n obj0 = %p class = %@ \n", array2[0], [array2[0] class]);
    NSLog(@"\n obj0 = %p class = %@ \n", array3[0], [array3[0] class]);
    
    NSLog(@"\n\n======== 元素是mutableString ========");
    NSLog(@"\n obj0 = %p class = %@ \n", array1[1], [array1[1] class]);
    NSLog(@"\n obj0 = %p class = %@ \n", array2[1], [array2[1] class]);
    NSLog(@"\n obj0 = %p class = %@ \n", array3[1], [array3[1] class]);

查看输出

2021-05-09 11:14:50.710409+0800 AlgorithmDemo[12261:67019] 
 array1 = 0x1006b9e40 class = __NSArrayI  (line1)
 array2 = 0x1006ba180 class = __NSArrayM  (line1)
 array3 = 0x1006b7410 class = __NSArrayI  (line1)

======== 元素是String ======== 
 obj0 = 0x100008220 class = __NSCFConstantString  (line1)
 obj0 = 0x100008220 class = __NSCFConstantString  (line1)
 obj0 = 0x1006b6d20 class = __NSCFString  (line1)

======== 元素是mutableString ========
 obj0 = 0x1006b9cb0 class = __NSCFString  (line1)
 obj0 = 0x1006ba0e0 class = __NSCFString  (line1)
 obj0 = 0x1006b70e0 class = __NSCFString  (line1)

根据输出，我们很明显得出如下结论

对Array归档并解档后，会生成新的Array对象
Array对象内的不可变元素进行了深拷贝
Array对象内的可变元素进行了深拷贝

由此，我们得出对如下总结

只深拷贝NSArray对象，我们用mutableCopy就可以
只深拷贝NSMutableArray对象，我们用Copy或mutableCopy都可以
深拷贝Array对象及内部元素，我们可以通过归档的方法解决

3. 重写`copyWithZone` `mutableCopyWithZone`的方式深拷贝自定义对象

我们写一个person类测试一下

//
//  Person.h
//  AlgorithmDemo
//
//  Created by Ternence on 2021/5/9.
//

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *nickname;

@end

测试代码如下

    Person *person = [[Person alloc] init];
    person.nickname = @"码代码的小马";
    
    NSMutableArray *array1 = [NSMutableArray arrayWithObjects:person, nil];
    
    NSArray *array2 = [array1 copy];
    NSMutableArray *array3 = [array1 mutableCopy];
    
    NSLog(@"\n array1 = %p class = %@", array1, [array1 class]);
    NSLog(@"\n array2 = %p class = %@", array2, [array2 class]);
    NSLog(@"\n array3 = %p class = %@", array3, [array3 class]);
    
    NSLog(@"\n\n======== 数组内元素 ======== ");
    NSLog(@"\n array1[0] = %p class = %@", array1[0], [array1[0] class]);
    NSLog(@"\n array2[0] = %p class = %@", array2[0], [array2[0] class]);
    NSLog(@"\n array3[0] = %p class = %@", array3[0], [array3[0] class]);

查看输出

2021-05-09 11:33:47.241685+0800 AlgorithmDemo[17319:89117] 
 array1 = 0x102a04450 class = __NSArrayM
 array2 = 0x102a04550 class = __NSSingleObjectArrayI
 array3 = 0x102a04570 class = __NSArrayM

======== 数组内元素 ======== 
 array1[0] = 0x102a042c0 class = Person
 array2[0] = 0x102a042c0 class = Person
 array3[0] = 0x102a042c0 class = Person

我们发现数组对象已经被深拷贝，但数组对象内的元素还是浅拷贝

是不是我们在定义Person类的时候没有重写方法呢？我们把改一下Person类的代码，并对NSMutableArray内元素进行copy

! 此处的copyWithZone mutableCopyWithZone方法里，我们应该对属性也进行copy

//
//  Person.m
//  AlgorithmDemo
//
//  Created by Ternence on 2021/5/9.
//

#import "Person.h"

@interface Person ()<NSCopying, NSMutableCopying, NSCoding>

@end

@implementation Person

- (id)copyWithZone:(NSZone *)zone {
    Person *person = [Person allocWithZone:zone];
    person.nickname = [self.nickname copy];
    return person;
}

- (id)mutableCopyWithZone:(NSZone *)zone {
    Person *person = [Person allocWithZone:zone];
    person.nickname = [self.nickname mutableCopy];
    return person;
}

@end

测试代码

    Person *person = [[Person alloc] init];
    person.nickname = @"码代码的小马";
    
    NSMutableArray *array1 = [NSMutableArray arrayWithObjects:person, nil];
    
    NSArray *array2 = [array1 copy];
    NSMutableArray *array3 = [array1 mutableCopy];
    NSMutableArray *array4 = [[NSMutableArray alloc] initWithArray:array1 copyItems:true];
    NSMutableArray *array5 = [[NSMutableArray alloc] initWithObjects:[array1[0] copy], nil];
    NSMutableArray *array6 = [[NSMutableArray alloc] initWithObjects:[array1[0] mutableCopy], nil];
    
    NSLog(@"\n array1 = %p class = %@", array1, [array1 class]);
    NSLog(@"\n array2 = %p class = %@", array2, [array2 class]);
    NSLog(@"\n array3 = %p class = %@", array3, [array3 class]);
    NSLog(@"\n array4 = %p class = %@", array4, [array4 class]);
    NSLog(@"\n array5 = %p class = %@", array5, [array5 class]);
    NSLog(@"\n array6 = %p class = %@", array6, [array6 class]);
    
    NSLog(@"\n\n======== 数组内元素 ========");
    Person *orgArrayObj = (Person *)array1[0];
    Person *newArrayObj2 = (Person *)array2[0];
    Person *newArrayObj3 = (Person *)array3[0];
    Person *newArrayObj4 = (Person *)array4[0];
    Person *newArrayObj5 = (Person *)array5[0];
    Person *newArrayObj6 = (Person *)array6[0];
    NSLog(@"\n array1[0] = %p nickname = %p", orgArrayObj, orgArrayObj.nickname);
    NSLog(@"\n array2[0] = %p nickname = %p", newArrayObj2, newArrayObj2.nickname);
    NSLog(@"\n array3[0] = %p nickname = %p", newArrayObj3, newArrayObj3.nickname);
    NSLog(@"\n array4[0] = %p nickname = %p", newArrayObj4, newArrayObj4.nickname);
    NSLog(@"\n array5[0] = %p nickname = %p", newArrayObj5, newArrayObj5.nickname);
    NSLog(@"\n array6[0] = %p nickname = %p", newArrayObj6, newArrayObj6.nickname);

继续查看打印结果

2021-05-10 11:18:25.020830+0800 AlgorithmDemo[98320:429537] 
 array1 = 0x10041a790 class = __NSArrayM
 array2 = 0x100419b60 class = __NSSingleObjectArrayI
 array3 = 0x10041a880 class = __NSArrayM
 array4 = 0x10041a9f0 class = __NSArrayM
 array5 = 0x10041aa20 class = __NSArrayM
 array6 = 0x10041ac70 class = __NSArrayM

======== 数组内元素 ========
 array1[0] = 0x10041a340 nickname = 0x1000083a0 
 array2[0] = 0x10041a340 nickname = 0x1000083a0
 array3[0] = 0x10041a340 nickname = 0x1000083a0
 array4[0] = 0x100417660 nickname = 0x1000083a0 
 array5[0] = 0x100415370 nickname = 0x1000083a0
 array6[0] = 0x100412300 nickname = 0x10041ad20

我们再根据打印归纳总结一下
对于重写copyWithZone:、mutableCopyWithZone:的自定义对象

[array copy]、[array mutableCopy] 只深拷贝了array对象，元素是浅拷贝
initWithArray:array1 copyItems:生成了新的array，且array内元素person是深拷贝，但person的属性仍然是浅拷贝（注:此处属性浅拷贝是因为：person是NSString对象, copyItems 调用的是copyWithZone, [NSString copy]是浅拷贝）
通过遍历array,对person分别copy, 会调用person的copyWithZone，此时NSArray是深拷贝，NSArray内元素person是深拷贝, person的属性参数是否深拷贝，取决于属性参数的类型(NSString浅拷贝， NSMutableString深拷贝)
通过遍历array,对person分别mutable copy,会调用person的mutableCopyWithZone,此时NSArray 是深拷贝，NSArray内元素是深拷贝，元素的属性参数也是深拷贝

此时我们知道了，要对自定义对象进行深拷贝，解决方案是重写copyWithZone、mutableCopyWithZone,调用对应的方法即可

4. 用归档的方式深拷贝自定义对象

先改一下person类

//
//  Person.m
//  AlgorithmDemo
//
//  Created by Ternence on 2021/5/9.
//

#import "Person.h"

@interface Person ()<NSCopying, NSMutableCopying, NSCoding>

@end

@implementation Person

- (instancetype)initWithCoder:(NSCoder *)coder {
    self.nickname = [coder decodeObjectForKey:@"nickname"];
    return  self;
}

- (void)encodeWithCoder:(NSCoder *)coder {
    [coder encodeObject:self.nickname forKey:@"nickname"];
}

@end

再改写测试代码

    Person *person = [[Person alloc] init];
    person.nickname = @"码代码的小马";
    NSMutableArray *array1 = [NSMutableArray arrayWithObjects:person, nil];
    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:array1];
    NSMutableArray *array2 = [NSKeyedUnarchiver unarchiveObjectWithData:data];
    
    NSLog(@"\n array1 = %p class = %@", array1, [array1 class]);
    NSLog(@"\n array2 = %p class = %@", array2, [array2 class]);
    
    NSLog(@"\n\n======== 数组内元素 ========");
    Person *orgArrayObj = (Person *)array1[0];
    Person *newArrayObj2 = (Person *)array2[0];
    NSLog(@"\n array1[0] = %p nickname = %p", orgArrayObj, orgArrayObj.nickname);
    NSLog(@"\n array2[0] = %p nickname = %p", newArrayObj2, newArrayObj2.nickname);

再耐心查看一下打印

2021-05-10 11:41:52.420699+0800 AlgorithmDemo[2252:455650] 
 array1 = 0x103b04e50 class = __NSArrayM
 array2 = 0x103b06f30 class = __NSArrayM

======== 数组内元素 ========
 array1[0] = 0x10061dcc0 nickname = 0x1000083a0
 array2[0] = 0x103b05860 nickname = 0x103b06120

很明显，array对象深拷贝了，array内的自定义对象person深拷贝了，自定义对象person的nickname也深拷贝了

我们来对Array的拷贝做个年终总结:

copy：对NSArray对象是浅拷贝，可NSMutableArray对象是深拷贝
mutableCopy：始终是深拷贝
[Array copy]、[Array mutableCopy]因为只对Array对象本身做拷贝操作，对Array内的元素是浅拷贝
要实现Array内元素的深拷贝，本质是元素全都进行深拷贝操作
initWithArray:array1 copyItems:生成了新的array，copyItems:true只是调用了Array的copyWithZone方法,Array内元素是浅拷贝
通过归解档的方式，可以实现对array、array 内元素person、person属性nickname深拷贝

iOS - 如何深拷贝Array内元素、自定义对象、及自定义对象

探索过程

1. 系统Api

2. 归档

3. 重写`copyWithZone` `mutableCopyWithZone`的方式深拷贝自定义对象

4. 用归档的方式深拷贝自定义对象

我们来对Array的拷贝做个年终总结:

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热点阅读

iOS - 如何深拷贝Array内元素、自定义对象、及自定义对象

探索过程

1. 系统Api

2. 归档

3. 重写copyWithZone mutableCopyWithZone的方式深拷贝自定义对象

4. 用归档的方式深拷贝自定义对象

我们来对Array的拷贝做个年终总结:

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读

3. 重写`copyWithZone` `mutableCopyWithZone`的方式深拷贝自定义对象