针对NSString的copy修饰前后，引用计数的变化

Posted 2020-07-25 拳不离手

 1         NSLog(@"NSString的对象，用NSString来接---------------------------------");
 2         NSString *string1 = [[NSString alloc]initWithFormat:@"不可变字符串"];
 3         NSLog(@"copy前，不可变字符串的引用计数 = %ld", [string1 retainCount]);
 4         
 5         NSString *copyString1 = string1.copy;
 6         NSLog(@"copy后，不可变字符串的引用计数 = %ld", [string1 retainCount]);
 7         NSLog(@"copy后，copyString的引用计数 = %ld", [copyString1 retainCount]);
 8         
 9         NSLog(@"%p", string1);
10         NSLog(@"%p", copyString1);
11         NSLog(@"NSMutableString的对象，用NSMutableString来接---------------------------------");
12         NSMutableString *string2 = [[NSMutableString alloc]initWithFormat:@"可变字符串"];
13         NSLog(@"copy前，可变字符串的引用计数 = %ld", [string2 retainCount]);
14         
15         NSMutableString *copyString2 = string2.copy;
16         NSLog(@"copy后，可变字符串的引用计数 = %ld", [string2 retainCount]);
17         NSLog(@"copy后，copyString的引用计数 = %ld", [copyString2 retainCount]);
18         
19         NSLog(@"%p", string2);
20         NSLog(@"%p", copyString2);
21         NSLog(@"NSString的对象，用NSMutableString来接---------------------------------");
22         NSString *string3 = [[NSString alloc]initWithFormat:@"不可变字符串"];
23         NSLog(@"copy前，不可变字符串的引用计数 = %ld", [string3 retainCount]);
24         
25         NSMutableString *copyString3 = string3.copy;
26         NSLog(@"copy后，不可变字符串的引用计数 = %ld", [string3 retainCount]);
27         NSLog(@"copy后，copyString的引用计数 = %ld", [copyString3 retainCount]);
28         
29         NSLog(@"%p", string3);
30         NSLog(@"%p", copyString3);
31         NSLog(@"NSMutableString的对象，用NSString来接---------------------------------");
32         NSMutableString *string4 = [[NSMutableString alloc]initWithFormat:@"可变字符串"];
33         NSLog(@"copy前，可变字符串的引用计数 = %ld", [string4 retainCount]);
34         
35         NSString *copyString4 = string4.copy;
36         NSLog(@"copy后，可变字符串的引用计数 = %ld", [string4 retainCount]);
37         NSLog(@"copy后，copyString的引用计数 = %ld", [copyString4 retainCount]);
38         
39         NSLog(@"%p", string4);
40         NSLog(@"%p", copyString4);

先来看看上面的运行结果，都打印出什么： 1 2016-06-15 11:39:06.411 OCLession9[1810:63941] NSString的对象，用NSString来接---------------------------------

 2 2016-06-15 11:39:06.411 OCLession9[1810:63941] copy前，不可变字符串的引用计数 = 1
 3 2016-06-15 11:39:06.411 OCLession9[1810:63941] copy后，不可变字符串的引用计数 = 2
 4 2016-06-15 11:39:06.411 OCLession9[1810:63941] copy后，copyString的引用计数 = 2
 5 2016-06-15 11:39:06.411 OCLession9[1810:63941] 0x100202740
 6 2016-06-15 11:39:06.411 OCLession9[1810:63941] 0x100202740
 7 2016-06-15 11:39:06.412 OCLession9[1810:63941] NSMutableString的对象，用NSMutableString来接---------------------------------
 8 2016-06-15 11:39:06.412 OCLession9[1810:63941] copy前，可变字符串的引用计数 = 1
 9 2016-06-15 11:39:06.412 OCLession9[1810:63941] copy后，可变字符串的引用计数 = 1
10 2016-06-15 11:39:06.412 OCLession9[1810:63941] copy后，copyString的引用计数 = 1
11 2016-06-15 11:39:06.412 OCLession9[1810:63941] 0x100300840
12 2016-06-15 11:39:06.412 OCLession9[1810:63941] 0x100300810
13 2016-06-15 11:39:06.412 OCLession9[1810:63941] NSString的对象，用NSMutableString来接---------------------------------
14 2016-06-15 11:39:06.412 OCLession9[1810:63941] copy前，不可变字符串的引用计数 = 1
15 2016-06-15 11:39:06.412 OCLession9[1810:63941] copy后，不可变字符串的引用计数 = 2
16 2016-06-15 11:39:06.412 OCLession9[1810:63941] copy后，copyString的引用计数 = 2
17 2016-06-15 11:39:06.412 OCLession9[1810:63941] 0x100106f90
18 2016-06-15 11:39:06.412 OCLession9[1810:63941] 0x100106f90
19 2016-06-15 11:39:06.413 OCLession9[1810:63941] NSMutableString的对象，用NSString来接---------------------------------
20 2016-06-15 11:39:06.413 OCLession9[1810:63941] copy前，可变字符串的引用计数 = 1
21 2016-06-15 11:39:06.413 OCLession9[1810:63941] copy后，可变字符串的引用计数 = 1
22 2016-06-15 11:39:06.413 OCLession9[1810:63941] copy后，copyString的引用计数 = 1
23 2016-06-15 11:39:06.413 OCLession9[1810:63941] 0x1006002f0
24 2016-06-15 11:39:06.413 OCLession9[1810:63941] 0x100600210

结论：对字符串，只有对不可变字符串的不可变拷贝才是浅拷贝，其余的都是深拷贝。