Question

我有以下代码

NSMutableArray *mutArray = [[NSMutableArray alloc] init];
[mutArray addObject: [NSProcessInfo processInfo]];
[mutArray addObject: @"This is NSString Object"];
[mutArray addObject: [[NSMutableString alloc] initWithString: @"1st Mutable String"]];

for (id element in mutArray){
      NSLog(@" ");
      NSLog(@"Class Name: %@", [element className]);
      NSLog(@"Is Member of NSString: %@", ([element class] isMemberOfClass: [NSString class]) ? YES: NO);
      NSLog(@"Is kind of NSString: %@", ([element class] isKindOfClass: [NSString class]) ? YES: NO);
}

我得到了以下输出（并且期望指出）

Class Name: NSProcessInfo
Is Member of NSString: NO
Is Kind of NSString: NO

Class Name: NSCFString         <-- Expecting NSString
Is Member of NSString: NO      <-- Expecting YES
Is Kind of NSString: NO        <-- Expecting YES

Class Name: NSCFString         <-- Expecting NSMutableString
Is Member of NSString: NO      
Is Kind of NSString: NO        <-- Expecting YES

我在这里错过了一些可怕的简单吗？谢谢！

Answer 1

使用：

[element isMemberOfClass: [NSString class]]

不

[[element class] isMemberOfClass: [NSString class]]

NSString和NSMutableString实现为class cluster（参见iPhone version of the documentation中的“字符串对象”）。

所以isKindOfClass：应该返回true但isMemberOfClass：将返回false，因为NSString不是对象的确切类型。

Answer 2

NSString由一组类组成。它们也与CFString s（来自CoreFoundation）进行免费桥接。这很可能出现在NSString这个NSCFString的实现中（我不知道所有的事实，但我在这里的推论是这个类充当了桥梁。）

发送给对象的className和isKindOfClass消息

2 个答案: