什么是NSObject isEqual:和哈希默认函数? [英] What is the NSObject isEqual: and hash default function?

问题描述

我有一个数据库模型类，它是一个NSObject.我在NSMutableArray中有一组这些对象.我使用indexOfObject:查找匹配项.问题在于模型对象的内存地址发生了变化.因此，我重写了hash方法以返回模型的行ID.但是，这不能解决问题.我还必须重写isEqual:方法以比较hash方法的值.

I have a database model class that is a NSObject. I have a set of these objects in a NSMutableArray. I use indexOfObject: to find a match. Problem is the model object's memory address changes. So I am overriding the hash method to return the model's row ID. This however does not fix it. I also have to override the isEqual: method to compare the value of the hash method.

默认情况下，isEqual:方法用于确定相等性的是什么?

What does the isEqual: method use to determine equality by default?

我假设它使用内存地址.阅读 isEqual: 文档，我认为它使用了hash方法中的值.显然，情况并非如此，因为我尝试覆盖该值并不能解决我最初的问题.

I'm assuming it uses the memory address. After reading the isEqual: documentation I thought it used the value from the hash method. Obviously, that is not the case as my attempt to override that value did not solve my initial problem.

推荐答案

您已经正确地猜到了，NSObject的默认isEqual:行为是比较对象的内存地址.奇怪的是，目前

As you've correctly guessed, NSObject's default isEqual: behaviour is comparing the memory address of the object. Strangely, this is not presently documented in the NSObject Class Reference, but it is documented in the Introspection documentation, which states:

isEqual:的默认NSObject实现仅检查指针是否相等.

The default NSObject implementation of isEqual: simply checks for pointer equality.

当然，正如您毫无疑问地知道的那样，NSObject的子类可以覆盖isEqual:以表现不同.例如，NSString的isEqual:方法在传递另一个NSString时，将首先检查地址，然后检查字符串之间的确切文字匹配.

Of course, as you are doubtless aware, subclasses of NSObject can override isEqual: to behave differently. For example, NSString's isEqual: method, when passed another NSString, will first check the address and then check for an exact literal match between the strings.

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