天天看点
返回

复制对象（一）copy和mutableCopy方法

通过copy方法可以创建可变对象或不可变对象的不可变副本，对于不可变副本，其对象的值不可以改变。

通过mutableCopy方法可以创建可变对象或不可变对象的可变副本，对于可变副本其对象是可变的。

复制分为浅复制和深复制两种：浅复制只是复制指向对象的指针，并没有复制对象的具体内容。深复制则创建了要复制对象的具体内容，并返回指向对象副本的指针。

对于复制Foundation中的对象，默认并不是深复制，例如copy NSMutableArray对象是浅复制，只是对其指针进行复制；而copy NSMutableString对象是深复制，对原来引用的对象的具体内容也进行了复制。

对于NSString *str，指针str指向对象STRING，假设str指向的内存为2000号，那么2000号内存的内容就是STRING对象的内容。对str指针进行复制时，例如NSString *str2 = [str copy]，复制后str2指向的地址也是2000号，因此复制的就是STRING对象的内存地址，实现的是浅复制。测试结果：

NSString *str = @"1";
        NSString *str2 = [str copy];
        NSLog(@"%p", str);
        NSLog(@"%p", str2);
        NSLog(@"%@", str);
        NSLog(@"%@", str2);
        str = @"new 1"; // 改变str的指向，不会影响str2的指向
        NSLog(@"--------------------");
        NSLog(@"%p", str);
        NSLog(@"%p", str2);
        NSLog(@"%@", str);
        NSLog(@"%@", str2);
           
2014-02-03 11:09:57.332 a[766:303] 0x100001050
2014-02-03 11:09:57.333 a[766:303] 0x100001050
2014-02-03 11:09:57.334 a[766:303] 1
2014-02-03 11:09:57.334 a[766:303] 1
2014-02-03 11:09:57.334 a[766:303] --------------------
2014-02-03 11:09:57.334 a[766:303] 0x1000010b0
2014-02-03 11:09:57.335 a[766:303] 0x100001050
2014-02-03 11:09:57.335 a[766:303] new 1
2014-02-03 11:09:57.335 a[766:303] 1

对于NSMutableString *mstr，mstr指向对象MSTRING，其内存地址为3000。令NSMutableString *mstr2 = [mstr copy]，复制后mstr指向的地址为3010，3010号地址保存着MSTRING的副本，这里实现的是深复制。测试结果：

NSMutableString *mstr = [NSMutableString stringWithString:@"1"];
        NSMutableString *mstr2 = [mstr mutableCopy];
        NSLog(@"%p", mstr);
        NSLog(@"%p", mstr2);
        NSLog(@"%@", mstr);
        NSLog(@"%@", mstr2);
        [mstr appendString:@" append"]; // 改变mstr指向的对象的内容，不会影响到mstr2指向的对象副本
        NSLog(@"--------------------");
        NSLog(@"%p", mstr);
        NSLog(@"%p", mstr2);
        NSLog(@"%@", mstr);
        NSLog(@"%@", mstr2);
           
2014-02-03 11:10:18.795 a[777:303] 0x100204210
2014-02-03 11:10:18.796 a[777:303] 0x100204320
2014-02-03 11:10:18.796 a[777:303] 1
2014-02-03 11:10:18.797 a[777:303] 1
2014-02-03 11:10:18.797 a[777:303] --------------------
2014-02-03 11:10:18.797 a[777:303] 0x100204210
2014-02-03 11:10:18.797 a[777:303] 0x100204320
2014-02-03 11:10:18.797 a[777:303] 1 append
2014-02-03 11:10:18.798 a[777:303] 1

对于NSMutableArray *array，假设指针array指向的内存是2000号，那么从2000号开始将连续依次地存放着数组对象的地址，例如2000号地址中保存着对象obj1的地址，2002号地址保存着对象obj2的地址，2004号地址保存着对象obj3的地址。通过内存地址可以访问对象。

对array指向的内容进行复制，例如NSMutableArray *array2 = [array copy]，将另外为array2分配一块内存空间，假设复制后的array2指向2010号，其中2010号地址保存着对象指针array[0]的副本（指向obj1），2012号地址保存着指针array[1]的副本（指向obj2）等。换言之，复制的是对象指针的集合，并没有对真正的对象obj1等进行复制，所以实现的是浅复制。

测试结果：

（1）直接赋值，marray和marray2指向同一块内存区域，该内存区域上保持着指向对象的指针集合

NSMutableArray *marray = [NSMutableArray arrayWithObjects:@"1", @"2", @"3", nil];
        NSMutableArray *marray2 = marray; // 直接赋值
        
        marray[0] = @"new 1"; // 改变marray[0]的指向，将会影响到marray2[0]的指向
        NSLog(@"marray指向%p， 指向的内容：%@", marray, marray);
        NSLog(@"marray2指向%p，指向的内容：%@", marray2, marray2);
        
        marray = [NSMutableArray arrayWithObjects:@"4", @"5", @"6", nil]; // 改变marray的指向，将不会影响marray2指向的内容
        NSLog(@"marray指向%p， 指向的内容：%@", marray, marray);
        NSLog(@"marray2指向%p，指向的内容：%@", marray2, marray2);
           
2014-02-03 11:26:47.406 a[867:303] marray指向0x100201b70， 指向的内容：(
    "new 1",
    2,
    3
)
2014-02-03 11:26:47.408 a[867:303] marray2指向0x100201b70，指向的内容：(
    "new 1",
    2,
    3
)
2014-02-03 11:26:47.408 a[867:303] marray指向0x1002061b0， 指向的内容：(
    4,
    5,
    6
)
2014-02-03 11:26:47.408 a[867:303] marray2指向0x100201b70，指向的内容：(
    "new 1",
    2,
    3
)

（2）复制，marray和marray2指向不同的内存区域，但是两块内存地址中保存的内容都是指向对象的指针集合

NSMutableArray *marray = [NSMutableArray arrayWithObjects:
                                  [NSMutableString stringWithString:@"1"],
                                  [NSMutableString stringWithString:@"2"],
                                  [NSMutableString stringWithString:@"3"],
                                  nil];
        NSMutableArray *marray2 = [marray copy];
        
        NSMutableString *mstr = marray[0];
        [mstr appendString:@" append"]; // 改变marray[0]指向的对象的内容，将会影响到marray2[0]指向的内容
        NSLog(@"marray指向%p， 该地址上的指针指向的对象：%@", marray, marray);
        NSLog(@"marray2指向%p，该地址上的指针指向的对象：%@", marray2, marray2);
        
        marray[0] = @"new 1"; // 改变marray[0]的指向，将不会影响到marray2[0]的指向
        NSLog(@"marray指向%p， 该地址上的指针指向的对象：%@", marray, marray);
        NSLog(@"marray2指向%p，该地址上的指针指向的对象：%@", marray2, marray2);
           
2014-02-03 11:02:47.645 a[682:303] marray指向0x100201b70， 该地址上的指针指向的对象：(
    "1 append",
    2,
    3
)
2014-02-03 11:02:47.646 a[682:303] marray2指向0x1002045e0，该地址上的指针指向的对象：(
    "1 append",
    2,
    3
)
2014-02-03 11:02:47.646 a[682:303] marray指向0x100201b70， 该地址上的指针指向的对象：(
    "new 1",
    2,
    3
)
2014-02-03 11:02:47.646 a[682:303] marray2指向0x1002045e0，该地址上的指针指向的对象：(
    "1 append",
    2,
    3
)

对于NSArray对象，copy时连浅复制都没有进行，而是相当于直接赋值。例如NSArray *array, *array2, *array3，对于array2 = array和array3 = [array copy]，假设array指针指向内存2000号，那么array2和array3指向的也是2000号。可以使用%p输出指针来对比查看。

NSArray *array = @[@"1", @"2", @"3"];
        NSArray *array2 = array;
        NSArray *array3 = [array copy];
        NSLog(@"%p", array);
        NSLog(@"%p", array2);
        NSLog(@"%p", array3);
        NSLog(@"-----------");
        array = @[@"4", @"5", @"6"]; // 改变array的指向，不影响array2和array3的指向
        NSLog(@"%p", array);
        NSLog(@"%p", array2);
        NSLog(@"%p", array3);
           
2014-02-03 11:11:11.708 a[790:303] 0x100204960
2014-02-03 11:11:11.709 a[790:303] 0x100204960
2014-02-03 11:11:11.709 a[790:303] 0x100204960
2014-02-03 11:11:11.709 a[790:303] -----------
2014-02-03 11:11:11.709 a[790:303] 0x100300540
2014-02-03 11:11:11.710 a[790:303] 0x100204960
2014-02-03 11:11:11.710 a[790:303] 0x100204960

再看一下复制后的各种情况：

1.NSMutableArray和NSArray

NSMutableArray *marray1 = [NSMutableArray arrayWithObjects:
                                   [NSMutableString stringWithString:@"1"],
                                   [NSMutableString stringWithString:@"2"],
                                   [NSMutableString stringWithFormat:@"3"],
                                   nil];
        NSMutableArray *marray2 = [marray1 mutableCopy];
        NSArray *array1 = [marray1 copy];
        NSArray *array2 = [marray1 mutableCopy];

（1）添加字符串到marray1[0]中：

// append string to marray1[0]
        NSMutableString *mstr = marray1[0];
        [mstr appendString:@" append"];
        NSLog(@"append string to marray1[0]");
        NSLog(@"marray1 = %@", marray1);
        NSLog(@"marray2 = %@", marray2);
        NSLog(@"array1 = %@", array1);
        NSLog(@"array2 = %@", array2);
           
2014-01-31 21:10:39.097 Array[298:303] append string to marray1[0]
2014-01-31 21:10:39.098 Array[298:303] marray1 = (
    "1 append",
    2,
    3
)
2014-01-31 21:10:39.098 Array[298:303] marray2 = (
    "1 append",
    2,
    3
)
2014-01-31 21:10:39.098 Array[298:303] array1 = (
    "1 append",
    2,
    3
)
2014-01-31 21:10:39.099 Array[298:303] array2 = (
    "1 append",
    2,
    3
)

分析：

将marray1[0]指向的对象地址赋给mstr指针，并对mstr指向的对象进行修改，将造成对象层次的修改，所以append会影响到所有数组的输出。

（2）为marray1[0]设置新的对象值：（注意（2）、（3）和（1）是相互独立的，下同）

// set new object to marray1[0]
        marray1[0] = [NSMutableString stringWithString:@"new 1"];
        NSLog(@"set new object to marray1[0]");
        NSLog(@"marray1 = %@", marray1);
        NSLog(@"marray2 = %@", marray2);
        NSLog(@"array1 = %@", array1);
        NSLog(@"array2 = %@", array2);
           
2014-01-31 20:50:52.003 Array[4151:303] set new object to marray1[0]
2014-01-31 20:50:52.004 Array[4151:303] marray1 = (
    "new 1",
    2,
    3
)
2014-01-31 20:50:52.005 Array[4151:303] marray2 = (
    1,
    2,
    3
)
2014-01-31 20:50:52.005 Array[4151:303] array1 = (
    1,
    2,
    3
)
2014-01-31 20:50:52.005 Array[4151:303] array2 = (
    1,
    2,
    3
)

分析：

这里创建了一个新的NSMutableString对象并将其内存地址赋给指针marray1[0]，而其他数组指针指向的对象不变，所以输出时其他数组不受影响。

（3）添加新的对象到marray1中：

// add new object to marray1
        [marray1 addObject:[NSMutableString stringWithString:@"4"]];
        NSLog(@"add new object to marray1");
        NSLog(@"marray1 = %@", marray1);
        NSLog(@"marray2 = %@", marray2);
        NSLog(@"array1 = %@", array1);
        NSLog(@"array2 = %@", array2);
           
2014-01-31 20:51:46.867 Array[4167:303] add new object to marray1
2014-01-31 20:51:46.869 Array[4167:303] marray1 = (
    1,
    2,
    3,
    4
)
2014-01-31 20:51:46.869 Array[4167:303] marray2 = (
    1,
    2,
    3
)
2014-01-31 20:51:46.869 Array[4167:303] array1 = (
    1,
    2,
    3
)
2014-01-31 20:51:46.869 Array[4167:303] array2 = (
    1,
    2,
    3
)

分析：

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marray1[3]中。而其他几个数组指针的引用不受影响。

（4）操作数组的引用

如果要单独替换marray1[0]指向的对象，应该先创建一个对象，然后再替换marray1[0]的引用。这样就不会对marray2[0]等指向的对象造成影响。

NSMutableArray *marray1 = [NSMutableArray arrayWithObjects:
                                   [NSMutableString stringWithString:@"1"],
                                   [NSMutableString stringWithString:@"2"],
                                   [NSMutableString stringWithFormat:@"3"],
                                   nil];
        NSMutableArray *marray2 = [marray1 mutableCopy];
        NSArray *array1 = [marray1 copy];
        NSArray *array2 = [marray1 mutableCopy];
        NSMutableString *mstr = [NSMutableString stringWithString:marray1[0]]; // 创建新的对象
        [mstr appendString:@" append"];
        [marray1 replaceObjectAtIndex:0 withObject:mstr]; // 替换marray1[0]的引用
        
        NSLog(@"marray1 = %@", marray1);
        NSLog(@"marray2 = %@", marray2);
        NSLog(@"array1 = %@", array1);
        NSLog(@"array2 = %@", array2);

控制台输出：

2014-01-31 20:09:33.678 Dictionary[3735:303] marray1 = (
    "1 append",
    2,
    3
)
2014-01-31 20:09:33.679 Dictionary[3735:303] marray2 = (
    1,
    2,
    3
)
2014-01-31 20:09:33.680 Dictionary[3735:303] array1 = (
    1,
    2,
    3
)
2014-01-31 20:09:33.680 Dictionary[3735:303] array2 = (
    1,
    2,
    3
)

再看一个例子：

NSMutableArray *marray1 = [NSMutableArray arrayWithObjects:
                                   [NSMutableString stringWithString:@"1"],
                                   [NSMutableString stringWithString:@"2"],
                                   [NSMutableString stringWithFormat:@"3"],
                                   nil];
        NSMutableArray *marray2 = [marray1 mutableCopy];
        NSArray *array1 = [marray1 copy];
        NSArray *array2 = [marray1 mutableCopy];
        
        [marray1 removeObjectAtIndex:0];
        
        NSLog(@"marray1 = %@", marray1);
        NSLog(@"marray2 = %@", marray2);
        NSLog(@"array1 = %@", array1);
        NSLog(@"array2 = %@", array2);

控制台输出：

2014-01-31 20:10:40.716 Dictionary[3746:303] marray1 = (
    2,
    3
)
2014-01-31 20:10:40.717 Dictionary[3746:303] marray2 = (
    1,
    2,
    3
)
2014-01-31 20:10:40.717 Dictionary[3746:303] array1 = (
    1,
    2,
    3
)
2014-01-31 20:10:40.718 Dictionary[3746:303] array2 = (
    1,
    2,
    3
)

[marray1 removeObjectAtIndex:0]移除的是marray1指向的索引结合中的第一个元素，即移除的是对对象的引用，而不是移除数组中的第一个对象。所以不会影响到marray2，array1，array2。

2.NSMutableString和NSString

复制NSMutableString对象测试代码如下：

NSMutableString *mstr1 = [NSMutableString stringWithString:@"1"];
        NSMutableString *mstr2 = [mstr1 mutableCopy];
        NSString *str1 = [mstr1 copy];
        NSString *str2 = [mstr1 mutableCopy];
        
        [mstr1 appendString:@" append"];
        NSLog(@"mstr1 = %@", mstr1);
        NSLog(@"mstr2 = %@", mstr2);
        NSLog(@"str1 = %@", str1);
        NSLog(@"str2 = %@", str2);
           
2014-01-31 20:54:20.423 String[4221:303] mstr1 = 1 append
2014-01-31 20:54:20.424 String[4221:303] mstr2 = 1
2014-01-31 20:54:20.424 String[4221:303] str1 = 1
2014-01-31 20:54:20.424 String[4221:303] str2 = 1

分析：

对mstr1指向的对象STRING1进行复制，这里复制的是对象STRING1本身的内容，也就是mstr2，str1，str2将分别指向对象STRING2，STRING3，STRING4。对STRING1的修改（在后面附加字符串），将不会影响到其他几个引用指向的对象。

可见这里进行的是深复制。

注意不要改变copy后的对象的值，因为copy生成的对象是不可变的，强行修改会导致程序崩溃。

复制对象（一）copy和mutableCopy方法

控制台输出为：

2014-02-01 00:57:24.903 Array[792:303] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to mutate immutable object with appendString:'

3.NSMutableDictionary和NSDictionary

首先创建1个字典（字典中对应3个对象）和4个字典指针：

NSMutableString *obj1 = [NSMutableString stringWithString:@"obj1"];
        NSMutableString *obj2 = [NSMutableString stringWithString:@"obj2"];
        NSMutableString *obj3 = [NSMutableString stringWithString:@"obj3"];
        NSMutableDictionary *mdic1 = [NSMutableDictionary dictionaryWithObjects:@[obj1, obj2, obj3]
                                                                        forKeys:@[@"key1", @"key2", @"key3"]];
        NSMutableDictionary *mdic2 = [mdic1 mutableCopy];
        NSDictionary *dic1 = [mdic1 copy];
        NSDictionary *dic2 = [mdic1 copy];

对字典进行复制也是浅复制。可以将字典的索引看做数组中的下标索引，所以其原理和数组的复制是一样的。

（1）添加字符串到mdic1的key1对应的可变字符串对象后：

// append string to mdic1[@"key1"]
        NSMutableString *mstr = mdic1[@"key1"];
        [mstr appendString:@" append"];
        NSLog(@"append string to midc1[@\"key1\"]");
        NSLog(@"mdic1 = %@", mdic1);
        NSLog(@"mdic2 = %@", mdic2);
        NSLog(@"dic1 = %@", dic1);
        NSLog(@"dic2 = %@", dic2);
           
2014-01-31 22:07:29.241 Dictionary[431:303] append string to midc1[@"key1"]
2014-01-31 22:07:29.242 Dictionary[431:303] mdic1 = {
    key1 = "obj1 append";
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:07:29.243 Dictionary[431:303] mdic2 = {
    key1 = "obj1 append";
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:07:29.243 Dictionary[431:303] dic1 = {
    key1 = "obj1 append";
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:07:29.243 Dictionary[431:303] dic2 = {
    key1 = "obj1 append";
    key2 = obj2;
    key3 = obj3;
}

（2）设置新的对象给key1：

// set new object for  key1
        NSMutableString *nobj1 = [NSMutableString stringWithString:@"new obj1"];
        [mdic1 setObject:nobj1 forKey:@"key1"];
        NSLog(@"set new object for key");
        NSLog(@"mdic1 = %@", mdic1);
        NSLog(@"mdic2 = %@", mdic2);
        NSLog(@"dic1 = %@", dic1);
        NSLog(@"dic2 = %@", dic2);
           
2014-01-31 22:08:01.617 Dictionary[448:303] set new object for key
2014-01-31 22:08:01.618 Dictionary[448:303] mdic1 = {
    key1 = "new obj1";
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:08:01.619 Dictionary[448:303] mdic2 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:08:01.619 Dictionary[448:303] dic1 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:08:01.619 Dictionary[448:303] dic2 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
}

（3）在字典中添加新的key-value对：

// add new key-value
        NSMutableString *obj4 = [NSMutableString stringWithString:@"obj4"];
        [mdic1 setObject:obj4 forKey:@"key4"];
        NSLog(@"add new key-value");
        NSLog(@"mdic1 = %@", mdic1);
        NSLog(@"mdic2 = %@", mdic2);
        NSLog(@"dic1 = %@", dic1);
        NSLog(@"dic2 = %@", dic2);
           
2014-01-31 22:12:14.678 Dictionary[466:303] add new key-value
2014-01-31 22:12:14.679 Dictionary[466:303] mdic1 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
    key4 = obj4;
}
2014-01-31 22:12:14.679 Dictionary[466:303] mdic2 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:12:14.679 Dictionary[466:303] dic1 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
}
2014-01-31 22:12:14.680 Dictionary[466:303] dic2 = {
    key1 = obj1;
    key2 = obj2;
    key3 = obj3;
}

小结：

1.浅复制复制的是指向对象的指针，对指针的修改并不会影响到指向的对象，更不会影响到其他指针。深复制复制的是对象的内容，对对象的操作修改将影响到所有指向该对象的指针。

2.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，因此这里只复制指针可以节省开销。

oc 深复制和浅复制 copy mutableCopy
上一篇: 爬虫实战爬取58同城房源信息
下一篇: 由58同城爬虫浅谈量子力学人性的多重分身

继续阅读