如何在Objective-C中比较对象? [英] How do I compare objects in Objective-C?

问题描述

如何比较自定义类的两个对象?我的想法是在类中添加一个额外的方法，使我可以将当​​前对象与另一个相同类型的对象进行比较.

How do I compare two objects of a custom class? My idea was to add an additional method to the class in which I can compare the current object with another object of the same kind.

所以我可以编写自己的代码，比较类的每个字段.

So I can write my own code how each field of the class is compared.

这就是我要做的.还是有一些预定义的方法可以做到这一点?像NSString类的"isEqualTo"一样?

This is how I would do it. Or are there some predefined methods to do that? Like "isEqualTo" of the NSString class?

推荐答案

指向-isEqual:的指针是好的，但是如果实现-isEqual:，则绝对必须还要在其中实现-hash这样，如果两个对象为-isEqual:返回YES，它们也将为-hash返回相同的值.在不使用-hash的情况下实现isEqual:的情况会导致在使用诸如NSArray之类的Collection时出现一些非常令人惊讶的错误.

The pointers to -isEqual: are good, but if you implement -isEqual:, you absolutely must also implement -hash in such a way that if two objects return YES for -isEqual: they will also return the same value for -hash. Implementing isEqual: without also implementing -hash leads to some very surprising bugs when you use Collections like NSArray.

对于新开发人员，我倾向于建议不要重载-isEqual:.我建议改为使用与NSString相同的技术，并创建一个自定义-isEqualToFoo:(其中Foo是您的类)，直到您了解-isEqual:对集合的影响并特别希望这种行为.重载-isEqual:功能强大，但是您可以创建的错误非常微妙.在许多情况下，创建自己的自定义比较器会更安全，更清晰.

For new developers, I tend to recommend against overloading -isEqual:. I recommend instead using the same technique as NSString, and create a custom -isEqualToFoo: (where Foo is your class) until you understand the impact of -isEqual: on collections and specifically want this behavior. Overloading -isEqual: powerful, but the bugs you can create are subtle. Creating your own custom comparator is safer and clearer in many cases.

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