How to access to each attribute of an object array using a loop?

Question

I have a Person object:

class Person{
    var name: String
    var city: String
    var country: String

    init(name: String, city: String, country: String){
        self.name = name
        self.city = city
        self.country = country
    }
}

and two arrays. One array of Person objects and one with the names of each of the attributes of the array.

var values = [Person]()
var attributes = ["name","city","country"]

and for example if I add two new Person objects to the array:

values.append(Person(name: "Peter" as! String, city: "Paris" as! String, country: "France" as! String))
values.append(Person(name: "Andrew" as! String, city: "Madrid" as! String, country: "Spain" as! String))

I would like to retrieve each of the attributes of each object of the array.

If I want to retrieve all the attributes of the first element I can do:

values[0].name
values[0].city
values[0].country

but I would like to do it in the way:

let totalAttributes = attributes.count - 1
for i in 0...totalAttributes{
   var attribute = attributes[i]
   values[0].attribute
}

but this, as I supposed, did not work.

In this case I can do it manually because there are only three attributes but I will not like to do the same when I will have more than 20 attributes inside the object.

Is there a way to do it within a loop?

Thanks in advance!

You could try making a dictionary out of all the properties and then iterating over the keys of that dictionary in your loop, but this is a bit unsatisfying. Are you looking for a more generic and elegant answer to the question than that? — Marcus, Oct 11 '16 at 15:59
Also, have you seen this discussion: http://stackoverflow.com/questions/25463146/iterate-over-object-class-attributes-in-swift — Marcus, Oct 11 '16 at 16:02
Instead of making `attributes` as an array, making it a Dictionary would be much more easier. — Santosh, Oct 11 '16 at 16:28

Carien van Zyl · Answer 1 · 2016-10-11T16:42:10.337

2

You can make use of reflection and MirrorType

let firstObj = values[0]
let personMirror = Mirror(reflecting: firstObj)
for child in personMirror.children {
    let (propertyName, propertyValue) = child
    print(propertyName)
    print(propertyValue)
}

You can access a specific property by the property name.

Example: Get the value of property named name

personMirror.descendant("name")

edited Oct 11 '16 at 16:42

answered Oct 11 '16 at 16:18

Carien van Zyl

2,853
22
30

This could be the better answer if you show how to get a property's value given only the property name. – rmaddy Oct 11 '16 at 16:26
I edited my answer to include retrieving a property by it's name – Carien van Zyl Oct 11 '16 at 16:42

score 2 · Answer 2 · answered Oct 11 '16 at 16:22

2

Let your class inherit from NSObject, then you can get/set its properties by the provided methods:

class Person: NSObject {
    var name: String
    var city: String
    var country: String

    init(name: String, city: String, country: String){
        self.name = name
        self.city = city
        self.country = country
    }
}

Now you can use:

var person = Person(...)
...
person.setValue("Peter", forKey: "name")
...
let name = person.value(forKey: "name")

answered Oct 11 '16 at 16:22

zisoft

22,770
10
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73

So if I retrieve the data from database and I want to store it on values array, and I have 30 attributes for each Person object. Have I to write 30 lines, one for set each attribute inside the loop? – Francisco Romero Oct 13 '16 at 06:57
If you retrieve 30 pairs (`attributename` and `value`) you just need 1 line of code in your loop: `person.setValue(value, forKey: attributename)` – zisoft Oct 13 '16 at 07:02

Benjamin Lowry · Answer 3 · 2016-10-12T02:34:10.937

If you add a function that returns the attributes of your Person class, then you should be able to do what you want. How you would process these values is another story. Below is an example of how you would change your Person class:

class Person{
    var name: String
    var city: String
    var country: String

    init(name: String, city: String, country: String){
        self.name = name
        self.city = city
        self.country = country
    }

    func returnAttributes() -> [AnyObject]{
        return [name, city, country]
    }
}

With your current scenario, you could also have the return type be [String], but it sounds like you are looking for a solution that allows for flexibility in terms of what types of objects its returning, so perhaps [AnyObject] is best.

So then you could do something like this:

let totalAttributes = attributes.count - 1
for i in 0...totalAttributes{
    values[0].returnAttributes //returns (for example): ["Peter", "Paris", "France"]
}

I am using Swift 3 and it does not recognize Object. Should it be NSObject? — Francisco Romero, Oct 11 '16 at 16:17
Thanks for pointing that out, I guess my playground didn't catch that. I would use AnyObject in this case. — Benjamin Lowry, Oct 12 '16 at 02:33

How to access to each attribute of an object array using a loop?

3 Answers3