Why are certain variables turning up nil? - json

Question

I'm trying to decode this json but certain variables are nil. Most of these seem to be okay it's just a few that are not working properly. I don't have much experience with swift so I'm kind of at a loss of what to try next.
mycode:
struct Attr : Decodable {
let page: String?
let perpage: String?
let totalpages: String?
let total: String?
}
struct Images : Decodable {
let text: String?
let size: String?
}
struct Artist : Decodable {
let name: String?
let mbid: String?
let url: String?
}
struct Streamable : Decodable {
let text: String?
let fulltrack: String?
}
struct Track : Decodable {
let name: String?
let duration: String?
let playcount: String?
let listeners: String?
let mbid: String?
let url: String?
let streamable: Streamable?
let artist: Artist?
let images: [Images]?
}
struct Tracks : Decodable {
let track:[Track]?
}
struct Container : Decodable {
let tracks: Tracks?
let attr: Attr?
}
json:
{
"tracks": {
"track": [
{
"name": "bad guy",
"duration": "0",
"playcount": "870682",
"listeners": "125811",
"mbid": "",
"url": "https://www.last.fm/music/Billie+Eilish/_/bad+guy",
"streamable": {
"#text": "0",
"fulltrack": "0"
},
"artist": {
"name": "Billie Eilish",
"mbid": "",
"url": "https://www.last.fm/music/Billie+Eilish"
},
"image": [
{
"#text": "https://lastfm-img2.akamaized.net/i/u/34s/88d7c302d28832b53bc9592ccb55306b.png",
"size": "small"
},
{
"#text": "https://lastfm-img2.akamaized.net/i/u/64s/88d7c302d28832b53bc9592ccb55306b.png",
"size": "medium"
},
{
"#text": "https://lastfm-img2.akamaized.net/i/u/174s/88d7c302d28832b53bc9592ccb55306b.png",
"size": "large"
},
{
"#text": "https://lastfm-img2.akamaized.net/i/u/300x300/88d7c302d28832b53bc9592ccb55306b.png",
"size": "extralarge"
}
]
},
...
images should contain an array of Images instead of nil, the majority of the other variables seem to be okay though

Answer 1

This is because when dealing with decodable the keys used in your serialized data format have to match the property names; In your case, the Image type contains text and size properties but the json contains #text and size (text =/= #text); That's also applicable for the type name Images not image.
However, citing from Encoding and Decoding Custom Types:
If the keys used in your serialized data format don't match the
property names from your data type, provide alternative keys by
specifying String as the raw-value type for the CodingKeys
enumeration.
Add CodingKeys as:
struct Images : Decodable {
let text: String?
let size: String?
enum CodingKeys: String, CodingKey {
case text = "#text"
case size
}
}
Tip: it is useful to use try/catch when facing an error while decoding your data:
do {
let result = try JSONDecoder().decode(Images.self, from: data)
} catch {
print(error.localizedDescription)
}
At this point it would print the error which might helpful to understand the issue most of the time.

Answer 2

Add CodingKey enum to map fields with # in the name
struct Images : Decodable {
let text: String?
let size: String?
enum CodingKeys: String, CodingKey {
case text = "#text"
case size
}
}
struct Streamable : Decodable {
let text: String?
let fulltrack: String?
enum CodingKeys: String, CodingKey {
case text = "#text"
case fulltrack
}
}
You also have an error in your Trackstruct, change images to image (or use CodingKey mapping there to). For more on decoding json see Apple's doc