嵌入式NSArray中第一个元素的键路径 [英] Keypath for first element in embedded NSArray

问题描述

这个例子是人为设计的，但它说明了我的观点.

This example is contrived, but it shows my point.

所以，如果我有一个如下的对象图:

So, if I have an object graph like the following:

{
sex = male;
uid = 637650940;
work = ({
    employer = {
        id = 116420715044499;
        name = "Software Engineer";
    };
    "end_date" = "0000-00";
    "start_date" = "0000-00";
}, {
    employer = {
        id = 188733137832278;
        name = "Apple";
    };
});
},
//Some more objects

(这是包含对象类型为NSArray的NSDictionary的NSArray).

(This is an NSArray containing NSDictionarys that have an object of type NSArray).

关键字段是work.我想要一个键路径，该键路径将使用work数组中的第一个对象.

The key field is work. I want a Key Path that will take the first object in the work array.

如果我这样做:

NSArray* work = [outerArrayObject objectForKey: @"work"];
id name = [work valueForKeyPath: @"employer.name"];

我得到一个包含每个名称的数组(在上述情况下，为Software Engineer&Apple).是否有一个集合运算符或某种可以返回第一个对象的东西?如果您可以开发一个关键路径来按start_date对每个作品进行排序，也可以加分:)

I get an array containing each name (In the above case, Software Engineer & Apple). Is there a collection operator or something to return the first object? Bonus points if you can develop a Key Path to sort each work by start_date also :)

推荐答案

很好地回答我自己的问题，一种解决方法是:

Well to answer my own question, one way to do it is this:

1)定义以下类别

@implementation NSArray (CustomKVOOperators)

- (id) _firstForKeyPath: (NSString*) keyPath {
    NSArray* array = [self valueForKeyPath: keyPath];
    if( [array respondsToSelector: @selector(objectAtIndex:)] &&
        [array respondsToSelector: @selector(count)]) {
        if( [array count] )
            return [array objectAtIndex: 0];
        else
            return nil;
    }
    else {
        return nil;
    }
}

@end

2)使用此KeyPath语法

2) Use this KeyPath syntax

NSArray* work = [outerArrayObject objectForKey: @"work"];
id name = [work valueForKeyPath: @"@first.employer.name"];

感谢这个聪明的人.

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