- [NSObject isMemberOfClass：]方法有多有用？ [英] How useful is the -[NSObject isMemberOfClass:] method?

问题描述

这是一个我写的小测试程序：

Here's a small test program I wrote:

#import <Foundation/Foundation.h>

int main(int argc, char **argv) {   
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSArray *arr = [NSArray array];
    printf("Arr isMemberOfClass NSArray: %d\n", [arr isMemberOfClass:[NSArray class]]);
    printf("Arr isKindOfClass NSArray: %d\n", [arr isKindOfClass:[NSArray class]]); 

    [pool release];
    return 0;
}  

及其输出：

$ ./ismemberof   
Arr isMemberOfClass NSArray: 0   
Arr isKindOfClass NSArray: 1   

-isMemberOfClass：方法在任何Foundation类中有多有用？我理解这可能给我想要的类的类，我的子类，但对于Foundation类 - 我发现，对我的arr变量的结果是非直观的。这是因为NSArray不是一个具体的类，而是一个抽象类，而在下面的NSArray是真正的NSCFArray的具体实例。

How useful is the -isMemberOfClass: method in any of the Foundation classes? I understand this might give the desired results for classes which I subclass, but as for Foundation classes -- I find that a result of false for my arr variable is non-intuitive. Is the reason this happens because NSArray is not a concrete class but instead an abstract class, and underneath the hood NSArray is really a concrete instance of NSCFArray?

推荐答案

您通常需要 isKindOfClass：，而不是 isMemberOfClass：。区别是 isKindOfClass：将返回 YES 如果接收者是有问题类的子类的成员， isMemberOfClass：将在同一个案例中返回 NO 。

You generally want isKindOfClass:, not isMemberOfClass:. The difference is that isKindOfClass: will return YES if the receiver is a member of a subclass of the class in question, whereas isMemberOfClass: will return NO in the same case.

As Graham Lee指出， NSArray 是一个类集群。这意味着每个 NSArray 实例实际上是一个子类的实例 - 因此你的发现。只有 isKindOfClass：对于具有类集群的类成员测试很有用。

As Graham Lee points out, NSArray is a class cluster. That means that every NSArray instance is actually an instance of some subclass—hence your findings. Only isKindOfClass: is useful for class-membership testing with class clusters.

code> respondingToSelector：而不是类成员测试。一个例子是 objectEnumerator ，它也由 NSSet 和 NSDictionary （两者都是类集群）。一个例外是plist serialization：sets不是属性列表，所以你需要发送 allObjects 到你的集合，以获取一个数组，然后试图从它的plist数据。

That said, you generally should use respondsToSelector: rather than class-membership testing. One example would be objectEnumerator, which is also implemented by NSSet and NSDictionary (both of those also being class clusters). An exception would be plist serialization: sets aren't property lists, so you'd need to send allObjects to your set to get an array before trying to make plist data from it.

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