Convert JSON to Array Xcode

Question

I am trying to implement two side by side UIPickerViews, one for Type and the other for Subtype. Each is an array of strings

var typePickerData: [String] = [String]()
var subtypePickerData: [String] = [String]()

Each is a pretty simple array of names:

typePickerData = ["Monitor","Keyboard","Mouse"]

When the viewDidLoad fires or when a new Type is selected, the app makes a remote db call and I get a response containing JSON of subtype names which I want to use to populate and reload the subtype picker.

I am stuck on converting the response into subtypePickerData

let decoder = JSONDecoder()
    
if let jsonResponse = try? decoder.decode([String].self, from: data) {
        
    print("parse subtype response \(jsonResponse)")
        
    subtypePickerData = jsonResponse
    DispatchQueue.main.async {
        self.subtypePicker.reloadAllComponents()
    }
}

What am I doing wrong here converting the JSON response to subtypePickerData?

this is what I am getting from the remote call

result Optional(<__NSArrayM 0x281370e70>( { name = Monitor; },{ name = "AV Accessories"; },{ name = Computer; },{ name = "Monitor Stands"; },{ name = "Bracket/Mount"; },{ name = Screen; }

Here is my updated code after solving issue

    let decoder = JSONDecoder()

    if let jsonResponse = try? decoder.decode(Subtypes.self, from: data) {
        SubtypeList = jsonResponse.result
        self.subtypePickerData = SubtypeList.map{$0.Name}
        DispatchQueue.main.async {
            self.subtypePicker.reloadAllComponents()
        }
    }

What's wrong exactly? Is jsonResponse nil? Why try? and not a proper do/try/catch to see if there is an error? And what's the JSON looking like? — Larme
– Larme, Commented Jun 14, 2022 at 16:21
result Optional(<__NSArrayM 0x281370e70>( { name = Monitor; },{ name = "AV Accessories"; },{ name = Computer; },{ name = "Monitor Stands"; },{ name = "Bracket/Mount"; },{ name = Screen; } — Mike Volmar
– Mike Volmar, Commented Jun 14, 2022 at 17:03
What's that print? Where does it come from? What's your API call? And your JSON isn't a [String], just replace try? with try! you'll see... — Larme
– Larme, Commented Jun 14, 2022 at 17:26

burnsi · Accepted Answer · 2022-06-14 17:13:28Z

Yor response seems to be not type of [String] but an array of custom objects. You first need to create a struct to decode your response data to.

struct NameContainer{
    var name: String
}

then do:

//change decoding to String array to decoding array of custom object NameContainer
if let jsonResponse = try? decoder.decode([NameContainer].self, from: data) {
        
    print("parse subtype response \(jsonResponse)")
        
    subtypePickerData = jsonResponse.map{$0.name} // Map your objects to strings and assign them
    DispatchQueue.main.async {
        self.subtypePicker.reloadAllComponents()
    }
}

Remarks:

Never use try? this will obfuscate all errors. Use a proper do/catch block, handle the error or mark your function throws and handle the error up the chain.

pkamb · Accepted Answer · 2022-06-14 17:32:42Z

1

DispatchQueue.main.async {
    self.subtypePicker.reloadAllComponents()

Bracket/Mount"; },{ name = Screen; } –

edited Jun 14, 2022 at 17:32

pkamb

35.5k27 gold badges174 silver badges207 bronze badges

answered Jun 14, 2022 at 17:30

Hmo Bika

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2 Comments

burnsi Over a year ago

How does this answer adress the question?

General Grievance Over a year ago

Why the random partial string literal? Was this copied from somewhere?

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