Load text file into array struct

Question

This is the struct of my array:

struct Question {
    let imgName: String
    let questionText: String
    let options: [String]
    let correctAns: Int
    var wrongAns: Int
    var isAnswered: Bool
}

var questionsArray = [Question]()

Here is how the array is populated currently:

let que1 = Question(imgName: "img1", questionText: "What is 2 x 2 ?", options: ["2", "4", "8", "6"], correctAns: 1, wrongAns: -1, isAnswered: false)
let que2 = Question(imgName: "img2", questionText: "What is 4 + 2 ?", options: ["9", "4", "3", "6"], correctAns: 3, wrongAns: -1, isAnswered: false)
questionsArray = [que1, que2]

I would like to put data in a text file and populate my questionsArray. So I created a file, data.txt and put it into bundle. Below is the content of data.txt. Each question is separated by a new line.

Question(imgName: "img1", questionText: "What is 2 x 2 ?", options: ["2", "4", "8", "6"], correctAns: 1, wrongAns: -1, isAnswered: false)
Question(imgName: "img2", questionText: "What is 4 + 2 ?", options: ["9", "4", "3", "6"], correctAns: 3, wrongAns: -1, isAnswered: false)

I tried to use this method:

var arrayOfStrings: [String]?

do {
    if let path = Bundle.main.path(forResource: "data", ofType: "txt") {
        let data = try String(contentsOfFile:path, encoding: String.Encoding.utf8)
        arrayOfStrings = data.components(separatedBy: "\n")
        questionsArray = arrayOfStrings
    }
} catch let err as NSError {
    print(err)
}

However, I received an error, Cannot assign value of type '[String]?' to type '[Question]' for the line questionsArray = arrayOfStrings.

How to solve this?

Your arrayOfStrings is not yet set to an array of Question objects. So you try to set a [String] type to a variable of type [Question]. arrayOfStrings need to be first converted back to [Question] — Mindhavok
– Mindhavok, Commented May 2, 2018 at 12:05
arrayOfString is [String] and questionsArray is [Question]. The types clearly don't match. That's what the error message says. How are the single lines organized to separate the fields? I highly recommend to save the data as JSON or Property List and decode it directly into the struct. — vadian
– vadian, Commented May 2, 2018 at 12:06
Your questionsArray is array of Question struct and you are assigning array of string directly to array of your struct questionsArray. — iVarun
– iVarun, Commented May 2, 2018 at 12:07

vadian · Accepted Answer · 2018-05-02 12:30:55Z

This is a quick tutorial for a better data management. It uses widely your code.

Create a new Blank Playground, platform macOS (important!). You can keep the playground to add more questions.

Paste this code, it creates a JSON file questions.json on the desktop

struct Question : Encodable {
    let imgName: String
    let questionText: String
    let options: [String]
    let correctAns: Int
    var wrongAns: Int
    var isAnswered: Bool
}

let que1 = Question(imgName: "img1", questionText: "What is 2 x 2 ?", options: ["2", "4", "8", "6"], correctAns: 1, wrongAns: -1, isAnswered: false)
let que2 = Question(imgName: "img2", questionText: "What is 4 + 2 ?", options: ["9", "4", "3", "6"], correctAns: 3, wrongAns: -1, isAnswered: false)
let questionsArray = [que1, que2]

do {
    let jsonData = try JSONEncoder().encode(questionsArray)
    let url = URL(fileURLWithPath: NSHomeDirectory()).appendingPathComponent("Desktop/questions.json")
    try jsonData.write(to: url)
} catch {
    print(error)
}

Drag the file from the desktop into your project navigator. Make sure that Copy if needed is checked.

Use this code in your project

struct Question : Decodable {
    let imgName: String
    let questionText: String
    let options: [String]
    let correctAns: Int
    var wrongAns: Int
    var isAnswered: Bool
}

var questionsArray = [Question]()


let url = Bundle.main.url(forResource: "questions", withExtension: "json")!
let data = try! Data(contentsOf: url)
questionsArray = try! JSONDecoder().decode([Question].self, from: data)

Mindhavok · Accepted Answer · 2018-05-02 12:27:43Z

Saving the data in a file is a good idea. But in the format of txt and especially in this format below is definitely not a good idea :

Question(imgName: "img1", questionText: "What is 2 x 2 ?", options: ["2", "4", "8", "6"], correctAns: 1, wrongAns: -1, isAnswered: false)

You should use the json format which is perfectly suitable for this case. You save the data into a file.json.

How to do it ? Add the Codable protocol to your struct Question:

struct Question: Codable {
    let imgName: String
    let questionText: String
    let options: [String]
    let correctAns: Int
    var wrongAns: Int
    var isAnswered: Bool
}

Then encode the data :

do {
    let encodedData = try JSONEncoder().encode(questionsArray)
    // Write encoded data to file
} catch let err {
    print(err)
}

And when you want retrieve back the data:

let data = Data(contentsOf: url)
do {
    let decodedData = try JSONDecoder().decode([Question].self, from: data)
} catch let err {
    // Failed to decode data
    print(err)
}

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