Getting an NSArray of a single attribute from an NSArray

可紊 提交于 2019-12-18 15:34:37

问题


I am facing a very regular scenario.

I have an NSArray which has object of a custom type, say Person. The Person class has the attributes: firstName, lastName and age.

How can I get an NSArray containing only one attribute from the NSArray having Person objects?

Something like:

NSArray *people;
NSArray *firstNames = [people getArrayOfAttribute:@"firstName" andType:Person.Class]

I have a solution of writing a for loop and fill in the firstNames array but I don't want to do that.


回答1:


NSArray will handle this for you using KVC

NSArray *people ...;
NSArray *firstName = [people valueForKey:@"firstName"];

This will give you an array of the firstName values from each entry in the array




回答2:


Check out the filterUsingPredicate: method in NSMutableArray, basically you create a NSPredicate object that will define how the array will be filtered.

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Predicates/Articles/pUsing.html#//apple_ref/doc/uid/TP40001794-CJBDBHCB

This guide will give you an overview, and has a section for dealing with arrays.




回答3:


You can also use block based enumeration:

NSArray *people;  // assumably has a bunch of people
NSMutableArray *firstNames = [NSMutableArray array];

[people enumerateObjectsUsingBlock: 
 ^(id obj, NSUInteger idx, BOOL*flag){
     // filter however you want...
     [firstNames addObject:[Person firstName]];
 }];

The benefit is it is fast and efficient if you have a bunch of people...



来源:https://stackoverflow.com/questions/5968702/getting-an-nsarray-of-a-single-attribute-from-an-nsarray

易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!