为什么是[@“”“ class]!= NSClassFromString(NSStringFromClass([@“”class])) [英] Why is [@"" class] != NSClassFromString(NSStringFromClass([@"" class])) on OS X?
问题描述
if([@class] == NSClassFromString(NSStringFromClass([@class])))
printf(foo);
else
printf(bar);
iOS上的输出:foo
在OS X:bar
为什么这种行为在OS X上很奇怪?
有趣的问题。以下指出了注释中提到的一些事情:
类c1 = [@class];
Class c2 = NSClassFromString(NSStringFromClass([@class])));
//在iOS和OS X下的名称相同
NSLog(@c1:'%@',c2:'%@',c1,c2)
//指针在iOS下是相同的,但在OS X下是不同的
NSLog(@* c1:'%p',* c2:'%p',c1,c2)
if(c1 == c2){
NSLog(@== equal); // iOS
} else {
NSLog(@== not equal); // OS X
}
if([c1 isEqual:c2]){
NSLog(@isEqual:equal); // iOS
} else {
NSLog(@isEqual:not equal); // OS X
}
const char * n1 = class_getName(c1);
const char * n2 = class_getName(c2);
if(strcmp(n1,n2)== 0){
NSLog(@name equal); // iOS和OS X
} else {
NSLog(@name not equal);
}
在Mac(OS X 10.7.5) >
2013-05-07 12:35:45.249测试[27483:303] c1:'_ NSCFConstantString',c2:' _NSCFConstantString'
2013-05-07 12:40:06.673测试[27542:303] * c1:'0x7fff7d2bd740',* c2:'0x7fff7d28ae48'
2013-05 -07 12:35:45.250测试[27483:303] ==不等于
2013-05-07 12:35:45.251测试[27483:303] isEqual:不等于
在iOS(6.1)上,这提供了:a。在iOS(6.1)上,
2013-05-07 12:38:11.816测试[27516:11303] c1:'_ NSCFConstantString',c2: ' _NSCFConstantString'
2013-05-07 12:41:01.319测试[27557:11303] * c1:'0x1db88f8',* c2:'0x1db88f8'
2013-05-07 12:38:11.816测试[27516:11303] ==等于
2013-05-07 12:38:11.816测试[27516:11303] isEqual:等于
2013-05-07 12:38:11.816测试[27516:11303]名称相等
关键区别似乎是在iOS下,两个
Class
值是相同的对象,但在OS X下它们是两个不同的对象。
使用
==
或比较两个
Class
值似乎不安全isEqual: / code>,至少在OS X下。我找不到任何函数来比较两个类
的值,所以使用class_getName
似乎是最好的选择。if([@"" class] == NSClassFromString(NSStringFromClass([@"" class]))) printf("foo"); else printf("bar");
Output on iOS: foo
Output on OS X: bar
Why is this behaving that strange on OS X?
解决方案Interesting issue. The following points out some things mentioned in the comments:
Class c1 = [@"" class]; Class c2 = NSClassFromString(NSStringFromClass([@"" class])); // The names are the same under iOS and OS X NSLog(@"c1: '%@', c2: '%@'", c1, c2); // The pointers are the same under iOS but different under OS X NSLog(@"*c1: '%p', *c2: '%p'", c1, c2); if (c1 == c2) { NSLog(@"== equal"); // iOS } else { NSLog(@"== not equal"); // OS X } if ([c1 isEqual:c2]) { NSLog(@"isEqual: equal"); // iOS } else { NSLog(@"isEqual: not equal"); // OS X } const char *n1 = class_getName(c1); const char *n2 = class_getName(c2); if (strcmp(n1, n2) == 0) { NSLog(@"name equal"); // Both iOS and OS X } else { NSLog(@"name not equal"); }
On a Mac (OS X 10.7.5) this gives:
2013-05-07 12:35:45.249 Test[27483:303] c1: '_NSCFConstantString', c2: '_NSCFConstantString'
2013-05-07 12:40:06.673 Test[27542:303] *c1: '0x7fff7d2bd740', *c2: '0x7fff7d28ae48'
2013-05-07 12:35:45.250 Test[27483:303] == not equal
2013-05-07 12:35:45.251 Test[27483:303] isEqual: not equal
2013-05-07 12:35:45.251 Test[27483:303] name equalOn iOS (6.1) this gives:
2013-05-07 12:38:11.816 Test[27516:11303] c1: '_NSCFConstantString', c2: '_NSCFConstantString'
2013-05-07 12:41:01.319 Test[27557:11303] *c1: '0x1db88f8', *c2: '0x1db88f8'
2013-05-07 12:38:11.816 Test[27516:11303] == equal
2013-05-07 12:38:11.816 Test[27516:11303] isEqual: equal
2013-05-07 12:38:11.816 Test[27516:11303] name equalThe key difference seems to be that under iOS, the two
Class
values are the same object but under OS X they are two different objects.So it seems it is not safe to compare two
Class
values using==
orisEqual:
, at least under OS X. I couldn't find any function to compare twoClass
values so usingclass_getName
seems like the best alternative.这篇关于为什么是[@“”“ class]!= NSClassFromString(NSStringFromClass([@“”class]))的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!