How do I retrieve data from an API?

Question

I am running the following code and it keeps getting an error saying that found nil while unwrapping an optional. What am I doing wrong? I am using a good API.

Code Block languageclass Database_2020 {
		static let shared = Database_2020()
		var leagueNames: [String]
		var leagues: [[String]]
		let url = " https://www.someURL.com/service/"
		private func getData(from url: String) {
		
				let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, response, error in
			
				guard let data = data, error == nil else 
						print("something went wrong")
						return
				}
	
				var result: Response?
				do {
						result = try JSONDecoder().decode(Response.self, from: data)
				}
				catch {
						print("failed to convert \(error.localizedDescription)")
				}
				guard let json = result else {
						return
				}
				print(json.status)
				print(json.results.draftPosition)
				print(json.results.name)
		}
		task.resume()
		func printData() {
				getData(from: url)
		}
}

Swift
Xcode

2.4k

Posted by

japio

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Answer 1

Line 19:

Code Block 						result = try JSONDecoder().decode(Response.self, from: data)

How is Response defined ?

Posted by

Claude31

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Answer 2

an error saying that found nil while unwrapping an optional

Can you tell us on which line you get the error?

As far as I check your code, it has only one forced-unwrapping in this line.

Code Block 				let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, response, error in

Then I can find url used in the line above is defined as:

Code Block 		let url = " https://www.someURL.com/service/"

This is not a valid URL string, if the leading whitespace actually exists in your code.
Please try removing it:

Code Block 		let url = "https://www.someURL.com/service/"

Posted by

OOPer

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Answer 3

Yes, the leading whitespace had to be removed but now it is executing line 21 - 23. The error is 'The data couldn’t be read because it isn’t in the correct format.'

Thank you for your help.

Posted by

japio

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Answer 4

It looks like the API is in a dictionary? Does that matter on how I format the Struct?

Here is the actual API

Code Block languagehttps://www.fantasyfootballnerd.com/service/draft-rankings/json/fmt8fvc8xg2s/1/

Posted by

japio

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Answer 5

Line 19:

Code Block 						result = try JSONDecoder().decode(Response.self, from: data)

How is Response defined ?

Posted by

Claude31

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Answer 6

Does that matter on how I format the Struct?

I guess your Response does not match the actual response of the API.

And your code disposes some info of the error.

Change this line:

Code Block 						print("failed to convert \(error.localizedDescription)")

to:

Code Block 						print("failed to convert \(error)")

And see what's shown.

Posted by

OOPer

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Answer 7

Response is defined

Code Block languageimport Foundation
struct Response: Codable {
    let results: Player_Data
    let status: String
}
struct Player_Data: Codable {
    let playerID: String
    let position: String
    let displayName: String
    let fname: String
    let team: String
    let byeWeek: String
    let standDev: String
    let nerdRank: String
    let positionRank: String
    let overallRank: String
}

The error is

failed to convert keyNotFound(CodingKeys(stringValue: "results", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"results\", intValue: nil) (\"results\").", underlyingError: nil))

Posted by

japio

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Answer 8

The error is

failed to convert keyNotFound(CodingKeys(stringValue: "results", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "No value associated with key CodingKeys(stringValue: \"results\", intValue: nil) (\"results\").", underlyingError: nil))

The JSON text taken from the URL https://www.fantasyfootballnerd.com/service/draft-rankings/json/fmt8fvc8xg2s/1/ is outlined as:

Code Block {"PPR":1,"DraftRankings":[...]}

No "results" nor "status" in it.

The URL may be wrong or you may be using the wrong structs for the API.

A JSON-to-code service has shown this Swift code for the JSON text.

Code Block import Foundation
// MARK: - Response
struct Response: Codable {
    let ppr: Int?
    let draftRankings: [DraftRanking]?
    enum CodingKeys: String, CodingKey {
        case ppr = "PPR"
        case draftRankings = "DraftRankings"
    }
}
// MARK: - DraftRanking
struct DraftRanking: Codable {
    let playerId: String?
    let position: Position?
    let displayName, fname, lname: String?
    let team: Team?
    let byeWeek, standDev, nerdRank, positionRank: String?
    let overallRank: Int?
}
enum Position: String, Codable {
    case def = "DEF"
    case k = "K"
    case qb = "QB"
    case rb = "RB"
    case te = "TE"
    case wr = "WR"
}
enum Team: String, Codable {
    case ari = "ARI"
    case atl = "ATL"
    case bal = "BAL"
    case buf = "BUF"
    case car = "CAR"
    case chi = "CHI"
    case cin = "CIN"
    case cle = "CLE"
    case dal = "DAL"
    case den = "DEN"
    case det = "DET"
    case gb = "GB"
    case hou = "HOU"
    case ind = "IND"
    case jac = "JAC"
    case kc = "KC"
    case lac = "LAC"
    case lar = "LAR"
    case lv = "LV"
    case mia = "MIA"
    case min = "MIN"
    case ne = "NE"
    case no = "NO"
    case nyg = "NYG"
    case nyj = "NYJ"
    case phi = "PHI"
    case pit = "PIT"
    case sea = "SEA"
    case sf = "SF"
    case tb = "TB"
    case ten = "TEN"
    case was = "WAS"
}

Posted by

OOPer

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How do I retrieve data from an API?

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