IOS/Swift: Parse JSON data and dictionary

Question

I am trying to parse some nested JSON retrieved through an API but am having trouble isolating specific key-value pairs. In fact, I have some confusion over the difference between the JSON data and the dictionary obtained through serialization.

To retrieve the data I am using:

let task = URLSession.shared.dataTask(with: request) { data, response, error in
            guard let data = data, error == nil else {                                                 
                return
            }

To convert the data to a JSON dictionary, I am doing

do {
                let stringDic = try JSONSerialization.jsonObject(with: data, options: []) as? [String : Any]
            } catch let error {
                print(error)
            }

When printed, this produces nested output of the form:

Optional(["document_tone": {
    "tone_categories" =     (
                {
            "category_id" = "emotion_tone";
            "category_name" = "Emotion Tone";
  and so forth

My question is how can I get a unique value such as that for the key category_name?

If I try to use

let myCat = stringDic["category_name"]

Fix-it requires let document_tone = stringDic?["document_tone"] which if printed to console just prints whole dictionary over again.

Thanks in advance for any suggestions.

use json decoder with structs

ielyamani
– ielyamani

2018-09-22 16:22:29 +00:00
Commented Sep 22, 2018 at 16:22 — ielyamani
– ielyamani, Commented Sep 22, 2018 at 16:22

vadian · Accepted Answer · 2018-09-22 16:31:43Z

4

It's pretty easy: () is array, {} is dictionary and the compiler must know the static types of all subscripted objects:

if let documentTone = stringDic?["document_tone"] as? [String:Any],
   let toneCategories = documentTone["tone_categories"] as? [[String:Any]] {
   for category in toneCategories {
       print(category["category_name"])
   }
}

answered Sep 22, 2018 at 16:31

vadian

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2 Comments

user6631314 Over a year ago

What is difference between [String:Any] and [[String:Any]]

vadian Over a year ago

Dictionary ([String:Any]) vs. Array ([[String:Any]])

Shehata Gamal · Accepted Answer · 2018-09-22 17:08:10Z

2

I think it's better to use Decodable

struct Root:Decodable {
     let documentTone : InnerItem 
} 
struct InnerItem:Decodable {
     let toneCategories: [BottomItem] 
}  
struct BottomItem:Decodable {
     let categoryId: String
     let categoryName: String 
}

do {
   let decoder = JSONDecoder()
   decoder.keyDecodingStrategy = .convertFromSnakeCase
   let result = try decoder.decode(Root.self, from: data)
   //print all names 
   result.documentTone.toneCategories.forEach {print($0.categoryName) }
} catch {
  print(error)
}

edited Sep 22, 2018 at 17:08

answered Sep 22, 2018 at 16:48

Shehata Gamal

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2 Comments

vadian Over a year ago

You can omit all CodingKeys if you add the keyDecodingStrategy = .convertFromSnakeCase

Shehata Gamal Over a year ago

@vadian i think it's a good tip here , originally old parsed keys were not like that so i used to use codingKeys which let me drop that optimized way

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