iOS copy&mutableCopy理解

Copy&mutableCopy

 

• 通过copy方法可以创建可变或不可变对象的不可变副本，通过mutableCopy可以创建可变或不可变对象的可变副本。
• 拷贝分为浅拷贝和深拷贝：
  • 浅拷贝：指针拷贝，对一个对象进行浅拷贝，相当于对指向该对象的指针进行复制，产生一个新的指向这个对象的指针。当一个对象销毁后，两个指针都应该置空。
  • 深拷贝：内容拷贝，增加一个指针并且申请一个新的内存，使这个新增的指针指向这个新的内存。使用深拷贝不会出现浅拷贝时重复释放同一块内存的错误！

 

Not to say, show the code

 

一、NSArray

• 示例：不可变数组copy之后数组的地址没有变，是浅拷贝；mutableCopy之后数组的地址不同，但是里面的对象的地址相同，是深度为1的深拷贝。
  • NSArray *array = @[[NSMutableString stringWithString:@"a"], @"b"];
    NSArray *arrCopy = [array copy];
    NSArray *arrMurableCopy = [array mutableCopy];

    NSLog(@"arr address:                   %p", array);
    NSLog(@"arrCopy address:            %p",arrCopy);
    NSLog(@"arrMurableCopy address:%p", arrMurableCopy);

    NSLog(@"arr first address:                   %p", [array objectAtIndex:0]);
    NSLog(@"arrCopy first address:            %p", [arrCopy objectAtIndex:0]);
    NSLog(@"arrMurableCopy first address:%p", [arrMurableCopy objectAtIndex:0]);

    [self myNslog:array];
    [self myNslog:arrCopy];
    [self myNslog:arrMurableCopy];

    [array[0] appendString:@"aaa"];

    NSLog(@"arr address:                   %p", array);
    NSLog(@"arrCopy address:            %p",arrCopy);
    NSLog(@"arrMurableCopy address:%p", arrMurableCopy);

    NSLog(@"arr first address:                  %p", [array objectAtIndex:0]);
    NSLog(@"arrCopy first address:           %p", [arrCopy objectAtIndex:0]);
    NSLog(@"arrMurableCopy first address:%p", [arrMurableCopy objectAtIndex:0]);

    [self myNslog:array];
    [self myNslog:arrCopy];
    [self myNslog:arrMurableCopy];

  • arr address:                              0x146e5a9f0
    arrCopy address:                      0x146e5a9f0
    arrMurableCopy address:         0x146e3aa90
    arr first address:                       0x146e5a9b0
    arrCopy first address:               0x146e5a9b0
    arrMurableCopy first address:  0x146e5a9b0
    (
        a,
        b
    )
    (
        a,
        b
    )
    (
        a,
        b
    )
    arr address:                             0x146e5a9f0
    arrCopy address:                     0x146e5a9f0
    arrMurableCopy address:        0x146e3aa90
    arr first address:                      0x146e5a9b0
    arrCopy first address:              0x146e5a9b0
    arrMurableCopy first address: 0x146e5a9b0
    (
        aaaa,
        b
    )
    (
        aaaa,
        b
    )
    (
        aaaa,
        b
    )
• 不可变数组copy之后数组的地址没有变，是浅拷贝；mutableCopy之后数组的地址不同，但是里面的对象的地址相同，是深度为1的深拷贝。
• 从打印结果可以看出，打印的数组的第一个对象的地址相同，可见里面存放的是对象的内存地址, 并没有开辟内存空间存放对象。所以当为一个数组的第一个对象附加aaa后，所有数组的第一个对象值都变为aaaa

 

二、NSMutableArray

• 示例一：从结果可见，可变数组copy 和 mutableCopy之后数组的地址都不同，然而数组的第一个对象的地址都相同，说明没有开辟新的地址存放数组里面的对象，说明进行了深度为1的深拷贝，数组里面存的是 a , b 对象组成的数组的首地址。改变一个数组的第一个值，其他数组也发生变化。
  • // 可变数组
    NSMutableArray *mutableArr = [NSMutableArray arrayWithArray:@[[NSMutableString stringWithString:@"a"], @"b"]];
    NSMutableArray *mutableArrCopy = [mutableArr copy];
    NSMutableArray *mutableArrMutableCopy = [mutableArr mutableCopy];

    NSLog(@"mutableArr address:                   %p", mutableArr);
    NSLog(@"mutableArrCopy address:            %p", mutableArrCopy);
    NSLog(@"mutableArrMutableCopy address:%p", mutableArrMutableCopy);

    NSLog(@"mutableArr first address:                  %p", [mutableArr objectAtIndex:0]);
    NSLog(@"mutableArrCopy first address:           %p", [mutableArrCopy objectAtIndex:0]);
    NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);

    [self myNslog:mutableArr];
    [self myNslog:mutableArrCopy];
    [self myNslog:mutableArrMutableCopy];

    // 可变数组改变第一个值
    [mutableArr[0] appendString:@"aaa"];

    NSLog(@"mutableArr first address:                   %p", [mutableArr objectAtIndex:0]);
    NSLog(@"mutableArrCopy first address:            %p", [mutableArrCopy objectAtIndex:0]);
    NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);

    [self myNslog:mutableArr];
    [self myNslog:mutableArrCopy];
    [self myNslog:mutableArrMutableCopy];

  • mutableArr address:                            0x135e2e040
    mutableArrCopy address:                    0x135e19880
    mutableArrMutableCopy address:       0x135d0f0a0
    mutableArr first address:                     0x135d49580
    mutableArrCopy first address:             0x135d49580
    mutableArrMutableCopy first address:0x135d49580
    (
        a,
        b
    )
    (
        a,
        b
    )
    (
        a,
        b
    )
    mutableArr first address:                     0x135d49580
    mutableArrCopy first address:             0x135d49580
    mutableArrMutableCopy first address:0x135d49580
    (
        aaaa,
        b
    )
    (
        aaaa,
        b
    )
    (
        aaaa,
        b
    )
• 从结果可见，可变数组copy 和 mutableCopy之后数组的地址都不同，然而数组的第一个对象的地址都相同，说明没有开辟新的地址存放数组里面的对象，说明进行了深度为1的深拷贝，数组里面存的是 a , b 对象组成的数组的首地址。改变一个数组的第一个值，其他数组也发生变化。

 

• 示例二：这里创建一个新的可变字符串对象，并赋值给 mutableArr[0]，而其他数组指针指向的对象不变，所以输出时其他数组值不变。
  • // 设置新值
    mutableArr[0] = [NSMutableString stringWithString:@"A"];

    NSLog(@"mutableArr first address:%p", [mutableArr objectAtIndex:0]);
    NSLog(@"mutableArrCopy first address:%p", [mutableArrCopy objectAtIndex:0]);
    NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);

    [self myNslog:mutableArr];
    [self myNslog:mutableArrCopy];
    [self myNslog:mutableArrMutableCopy];

  • 设置新值之后的打印；
  • mutableArr first address:                     0x12f625590
    mutableArrCopy first address:             0x135d49580
    mutableArrMutableCopy first address:0x135d49580
    (
        A,
        b
    )
    (
        A,
        b
    )
    (
        A,
        b
    )
• 这里创建一个新的可变字符串对象，并赋值给 mutableArr[0]，而其他数组指针指向的对象不变，所以输出时其他数组值不变。

 

• 示例三：这里创建了一个新的可变字符串对象，并将其内存地址保存到指针mutableArr[3]中。而其他几个数组指针的引用不受影响。
  • // 添加新值
    [mutableArr addObject:[NSMutableString stringWithString:@"c"]];

    NSLog(@"mutableArr first address:                   %p", [mutableArr objectAtIndex:0]);
    NSLog(@"mutableArrCopy first address:            %p", [mutableArrCopy objectAtIndex:0]);
    NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);

    [self myNslog:mutableArr];
    [self myNslog:mutableArrCopy];
    [self myNslog:mutableArrMutableCopy];

  • mutableArr first address:                     0x135d49580
    mutableArrCopy first address:             0x135d49580
    mutableArrMutableCopy first address:0x135d49580
    (
        a,
        b,
        c
    )
    (
        a,
        b
    )
    (
        a,
        b
    )
• 这里创建了一个新的可变字符串对象，并将其内存地址保存到指针mutableArr[3]中。而其他几个数组指针的引用不受影响

 

• 示例四：操作的是mutableArr对对象的引用，所以不会影响到其他数组
  • // 操作数组的引用
    NSMutableString *mutableString = [NSMutableString stringWithString:mutableArr[0]];
    [mutableString appendString:@"aaa"];
    [mutableArr replaceObjectAtIndex:0 withObject:mutableString];

    NSLog(@"mutableArr first address:                  %p", [mutableArr objectAtIndex:0]);
    NSLog(@"mutableArrCopy first address:           %p", [mutableArrCopy objectAtIndex:0]);
    NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);

    [self myNslog:mutableArr];
    [self myNslog:mutableArrCopy];
    [self myNslog:mutableArrMutableCopy];

  • mutableArr first address:                     0x135d49570
    mutableArrCopy first address:             0x135d49580
    mutableArrMutableCopy first address:0x135d49580
    (
        aaaa,
        b,
        c
    )
    (
        a,
        b
    )
    (
        a,
        b
    )
  • // 操作数组的引用
    [mutableArr removeObjectAtIndex:1];

    NSLog(@"mutableArr first address:                   %p", [mutableArr objectAtIndex:0]);
    NSLog(@"mutableArrCopy first address:            %p", [mutableArrCopy objectAtIndex:0]);
    NSLog(@"mutableArrMutableCopy first address:%p", [mutableArrMutableCopy objectAtIndex:0]);

    [self myNslog:mutableArr];
    [self myNslog:mutableArrCopy];
    [self myNslog:mutableArrMutableCopy];

  • mutableArr first address:                     0x135d49580
    mutableArrCopy first address:             0x135d49580
    mutableArrMutableCopy first address:0x135d49580
    (
        a
    )
    (
        a,
        b
    )
    (
        a,
        b
    )
• 操作的是mutableArr对对象的引用，所以不会影响到其他数组

 

三、NSString

• 示例：copy 之后地址没有变，mutableCopy之后地址发生了变化，当改变了stringMutableCopy字符串之后，其他连个字符串没有发生变化，说明NSString copy 是浅拷贝，mutableCopy是深拷贝
  • NSString *string = @"abc";
    NSString *stringCopy = [string copy];
    NSMutableString *stringMutableCopy = [string mutableCopy];

    NSLog(@"string                   = %p", string);
    NSLog(@"stringCopy            = %p", stringCopy);
    NSLog(@"stringMutableCopy = %p", stringMutableCopy);

    [stringMutableCopy appendString:@"def"];

    NSLog(@"string                   = %p", string);
    NSLog(@"stringCopy            = %p", stringCopy);
    NSLog(@"stringMutableCopy = %p", stringMutableCopy);

    NSLog(@"string                   = %@", string);
    NSLog(@"stringCopy            = %@", stringCopy);
    NSLog(@"stringMutableCopy = %@", stringMutableCopy);

  • string                      = 0x1000f0310
    stringCopy              = 0x1000f0310
    stringMutableCopy = 0x14752fcf0
    string                      = 0x1000f0310
    stringCopy              = 0x1000f0310
    stringMutableCopy = 0x14752fcf0
    string                      = abc
    stringCopy              = abc
    stringMutableCopy = abcdef
• copy 之后地址没有变，mutableCopy之后地址发生了变化，当改变了stringMutableCopy字符串之后，其他连个字符串没有发生变化，说明NSString copy 是浅拷贝，mutableCopy是深拷贝

 

四、NSMutableString

• 示例：
  • NSMutableString *mutaleString = [NSMutableString stringWithString:@"a"];
    NSMutableString *mutaleStringcopy = [mutaleString copy];
    NSMutableString *mutaleStringmutableCopy = [mutaleString mutableCopy];

    NSLog(@"mutaleString                    = %p", mutaleString);
    NSLog(@"mutaleStringcopy             = %p", mutaleStringcopy);
    NSLog(@"mutaleStringmutableCopy = %p", mutaleStringmutableCopy);

    [mutaleString appendString:@"bcd"];

    NSLog(@"mutaleString                   = %p", mutaleString);
    NSLog(@"mutaleStringcopy             = %p", mutaleStringcopy);
    NSLog(@"mutaleStringmutableCopy = %p", mutaleStringmutableCopy);

    NSLog(@"mutaleString                    = %@", mutaleString);
    NSLog(@"mutaleStringcopy             = %@", mutaleStringcopy);
    NSLog(@"mutaleStringmutableCopy = %@", mutaleStringmutableCopy);

  • mutaleString                       = 0x14e637470
    mutaleStringcopy               = 0xa000000000000611
    mutaleStringmutableCopy = 0x14e6374b0
    mutaleString                       = 0x14e637470
    mutaleStringcopy               = 0xa000000000000611
    mutaleStringmutableCopy = 0x14e6374b0
    mutaleString                      = abcd
    mutaleStringcopy              = a
    mutaleStringmutableCopy = a
  • mutaleString = [NSMutableStringstringWithString:@"A"];

    NSLog(@"mutaleString                    = %p", mutaleString);
    NSLog(@"mutaleStringcopy             = %p", mutaleStringcopy);
    NSLog(@"mutaleStringmutableCopy = %p", mutaleStringmutableCopy);

    NSLog(@"mutaleString                    = %@", mutaleString);
    NSLog(@"mutaleStringcopy             = %@", mutaleStringcopy);
    NSLog(@"mutaleStringmutableCopy = %@", mutaleStringmutableCopy);

  • mutaleString                       = 0x14e637470
    mutaleStringcopy               = 0xa000000000000611
    mutaleStringmutableCopy = 0x14e6374b0
    mutaleString                       =  0x13c657000
    mutaleStringcopy               = 0xa000000000000611
    mutaleStringmutableCopy = 0x14e6374b0
    mutaleString                       = A
    mutaleStringcopy               = a
    mutaleStringmutableCopy = a
  • copy 和 mutableCopy都进行了深拷贝，开辟了 新的地址空间存储 拷贝后的变量；
  • 注意：copy 后的地址 0xa000000000000611 跟其他的不一样，copy后的对象是不可变的，强行修改会导致程序崩溃。
  • -[NSTaggedPointerString appendString:]: unrecognized selector sent to instance 0xa000000000000611
    *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSTaggedPointerString appendString:]: unrecognized selector sent to instance 0xa000000000000611'

 

五、NSMutableDictionary

• 示例一：mutableDict 的索引key1, key2, key3 分别对应对象 mutableStr1， mutableStr2， mutableStr3 的内存地址，copy 后所有的字典第一个对象的地址都相同，对字典拷贝也是浅拷贝。
  • NSMutableString *mutableStr1 = [NSMutableString stringWithString:@"a"];
    NSMutableString *mutableStr2 = [NSMutableString stringWithString:@"b"];
    NSMutableString *mutableStr3 = [NSMutableString stringWithString:@"c"];
    NSMutableDictionary *mutableDict = [NSMutableDictionary dictionaryWithObjects:@[mutableStr1, mutableStr2, mutableStr3] forKeys:@[@"key1", @"key2", @"key3"]];
    NSMutableDictionary *mutableDictCopy = [mutableDict copy];
    NSMutableDictionary *mutableDictMutableCopy = [mutableDict mutableCopy];

    NSLog(@"mutableDict                   = %p", mutableDict);
    NSLog(@"mutableDictCopy            = %p", mutableDictCopy);
    NSLog(@"mutableDictMutableCopy = %p", mutableDictMutableCopy);

    NSLog(@"mutableDict first address                    = %p", mutableDict[@"key1"]);
    NSLog(@"mutableDictCopy first address             = %p", mutableDictCopy[@"key1"]);
    NSLog(@"mutableDictMutableCopy first address  = %p", mutableDictMutableCopy[@"key1"]);

    [mutableDict[@"key1"] appendString:@"aaa"];

    NSLog(@"mutableDict                    = %@", mutableDict);
    NSLog(@"mutableDictCopy             = %@", mutableDictCopy);
    NSLog(@"mutableDictMutableCopy = %@", mutableDictMutableCopy);

    NSLog(@"mutableDict first address                    = %p", mutableDict[@"key1"]);
    NSLog(@"mutableDictCopy first address             = %p", mutableDictCopy[@"key1"]);
    NSLog(@"mutableDictMutableCopy first address  = %p", mutableDictMutableCopy[@"key1"]);

  • mutableDict                                            = 0x15f62f7d0
    mutableDictCopy                                    = 0x15f62f800
    mutableDictMutableCopy                       = 0x15f62f570
    mutableDict first address                       = 0x15f62f530
    mutableDictCopy first address               = 0x15f62f530
    mutableDictMutableCopy first address  = 0x15f62f530
    mutableDict            = {
        key1 = aaaa;
        key2 = b;
        key3 = c;
    }
    mutableDictCopy        = {
        key1 = aaaa;
        key2 = b;
        key3 = c;
    }
    mutableDictMutableCopy = {
        key1 = aaaa;
        key2 = b;
        key3 = c;
    }
    mutableDict first address                       = 0x15f62f530
    mutableDictCopy first address               = 0x15f62f530
    mutableDictMutableCopy first address  = 0x15f62f530
• mutableDict 的索引key1, key2, key3 分别对应对象 mutableStr1， mutableStr2， mutableStr3 的内存地址，copy 后所有的字典第一个对象的地址都相同，对字典拷贝也是浅拷贝。
• 对key1对应的对象mutableStr1进行修改后，由于指向同一个字典，所以输出相同，第一个对象的地址也相同。

 

• 示例二：
  • [mutableDict setObject:@"A" forKey:@"key1"];

    NSLog(@"mutableDict                   = %@", mutableDict);
    NSLog(@"mutableDictCopy            = %@", mutableDictCopy);
    NSLog(@"mutableDictMutableCopy = %@", mutableDictMutableCopy);

    NSLog(@"mutableDict first address                    = %p", mutableDict[@"key1"]);
    NSLog(@"mutableDictCopy first address             = %p", mutableDictCopy[@"key1"]);
    NSLog(@"mutableDictMutableCopy first address  = %p", mutableDictMutableCopy[@"key1"]);

  • mutableDict            = {
        key1 = A;
        key2 = b;
        key3 = c;
    }
    mutableDictCopy        = {
        key1 = a;
        key2 = b;
        key3 = c;
    }
    mutableDictMutableCopy = {
        key1 = a;
        key2 = b;
        key3 = c;
    }
    mutableDict first address                       = 0x1000fc390
    mutableDictCopy first address               = 0x15f62f530
    mutableDictMutableCopy first address  = 0x15f62f530

 

• mutableDict中key1存放的是第一个对象的内存地址，[mutableDict setObject:@"A" forKey:@"key1”]; 将key1中的内存地址修改为 @"A"的内存地址，不会影响到其他引用所指向的对象。

 

• 示例三：为 mutableDict 添加先得键值对，没有影响到其他字典指针，所以只有mutableDict发生变化。
  • [mutableDict setObject:@"d" forKey:@"key4"];

    NSLog(@"mutableDict                   = %@", mutableDict);
    NSLog(@"mutableDictCopy            = %@", mutableDictCopy);
    NSLog(@"mutableDictMutableCopy = %@", mutableDictMutableCopy);

    NSLog(@"mutableDict first address                    = %p", mutableDict[@"key1"]);
    NSLog(@"mutableDictCopy first address             = %p", mutableDictCopy[@"key1"]);
    NSLog(@"mutableDictMutableCopy first address  = %p", mutableDictMutableCopy[@"key1"]);

  • mutableDict            = {
        key1 = A;
        key2 = b;
        key3 = c;
        key4 = d;
    }
    mutableDictCopy        = {
        key1 = a;
        key2 = b;
        key3 = c;
    }
    mutableDictMutableCopy = {
        key1 = a;
        key2 = b;
        key3 = c;
    }
    mutableDict first address                       = 0x15f62f530
    mutableDictCopy first address               = 0x15f62f530
    mutableDictMutableCopy first address  = 0x15f62f530
• 为 mutableDict 添加先得键值对，没有影响到其他字典指针，所以只有mutableDict发生变化。

 

总结：NSMutableArray和NSMutableDictionary的复制是浅复制，NSMutableString的复制是深复制。由于数组或字典中对象数目或大小可能非常大，所以对对象的复制可能引起大量开销，因此这里只复制引用可以节省开销。