Xcode自动完成功能会提示神秘的&"songsAtIndexes&"用于NSArray吸气剂 [英] Xcode auto-complete suggests mysterious "songsAtIndexes" for NSArray getter

问题描述

我的类上有一个名为NSArray的属性，称为歌曲".我正在为此创建一个自定义吸气剂，而XCode为我提供了创建方法的选项:

I have a property of type NSArray on my class called "songs". I'm creating a custom getter for it and XCode gives me an option of creating a method:

songsAtIndexes:(NSIndexSet *)indexes

这是什么，为什么XCode提供此功能?这是特定于NSArray属性吗?为该方法创建方法/获取器的目的是什么?如果我没有手动定义它，会自动创建/合成它吗?

What is this and why is XCode offering this? Is this specific to NSArray properties? What is the purpose of creating a method/getter for this method? If I don't define it manually, will it be automatically created/synthesized?

推荐答案

这是对索引集合(可在您的类中使用)进行了很少使用的KVC优化的结果.您可以在此处上阅读.，但摘录:

This is the result of a little-used KVC optimization for indexed collections which can be used on your class. You can read about this here, but to excerpt:

索引到多对关系合规性

Indexed To-Many Relationship Compliance

对于建立索引的多对多关系，符合KVC要求您的课程:

For indexed to-many relationships, KVC compliance requires that your class:

• 实现一个名为-< key> 的方法，该方法返回一个数组.
• 或者有一个名为< key> 或 _< key> 的数组实例变量.
• 或实现方法 -countOf< Key> 和-objectInAtIndex:或-< key> AtIndexes:中的一个或两个.
• (可选)您还可以实现 -get< Key>:range:以提高性能.

• Implement a method named -<key> that returns an array.
• Or have an array instance variable named <key> or _<key>.
• Or implement the method -countOf<Key> and one or both of -objectInAtIndex: or -<key>AtIndexes:.
• Optionally, you can also implement -get<Key>:range: to improve performance.

它仅与带有KVC(有时为 NSPredicate s)的Core Data一起真正使用，但是您可以根据需要利用这些方法.

It's only really used with Core Data with KVC (and occasionally NSPredicates), but you can leverage these methods if you'd like to.

在99％的情况下，实现这一点实际上不是必需的，但是如果您愿意，也可以.

It's really not necessary in 99% of cases to implement this, but you can if you'd like.

这篇关于Xcode自动完成功能会提示神秘的&"songsAtIndexes&"用于NSArray吸气剂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！