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Fatal error: Failed to decode .json data from app bundle

import Foundation

struct RGBValue: Codable {
    let blue, green: Double
    let timestamp: String
    let red: Double
}

struct RGB: Codable {
    let fps: Double
    let heartRate: Int
    let rgbValues: [RGBValue]
    
    static let rgbData: [RGB] = Bundle.main.decode(file: "hrv_data.json")
    static let sampleData: RGB = rgbData[0]
}




extension Bundle{
    
    func decode<T: Decodable>(file: String) -> T {
        guard let url = self.url(forResource: file, withExtension: nil) else {
            fatalError("Could not find (file) in the project!")
        }
        guard let data = try? Data(contentsOf: url) else {
            fatalError("Could not load (file) in the project!")
        }
        
        let decoder = JSONDecoder()
        
        guard let loadedData = try? decoder.decode(T.self, from: data) else {
            fatalError("Could not decode (file) in the project! error : (Error.self)")

        }
        return loadedData
    }
}

This is the entire code snippet which shows no error, but while run time it crashes "Thread 1: Fatal error: Could not decode hrv_data.json in the project! error : Error"
How to solve the issue and know the reason behind this error?

json sample:

{
  "fps": 0.1548667699098587,
  "heartRate": 81,
  "rgbValues": [
    {
      "blue": 0,
      "green": 0,
      "timestamp": "22-04-2024 10:33:57",
      "red": 0
    }
  ]
}
Tags:

2

Answers


  1. 0

    I really appreciate Paul Hudson’s huge effort for the Swift community, but this Bundle extension he suggests to decode a JSON file is a poor advice, I’m afraid.

    It’s highly recommended to catch always the comprehensive DecodingError, it tells you exactly what’s wrong and even where the error occurred.

    Replace

    let loadedData = try? decoder.decode(T.self, from: data) else {
        fatalError("Could not decode (file) in the project! error : (Error.self)")
}
return loadedData

    with

    do {
    return try decoder.decode(T.self, from: data) 
} catch {
    fatalError("Could not decode (file) in the project! Error: (error)")
}

    The error is clear. The root object is a dictionary (note the enclosing {}), it’s not an array

    static let sampleData: RGB = Bundle.main.decode(file: "hrv_data.json")
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  2. 0

    Try this example code using decode with do/catch returning an optional,
    plus various improvements:

    struct RGBValue: Identifiable, Codable { //<-- here
    let id = UUID()
    
    let blue, green, red: Double
    let timestamp: String
    
    enum CodingKeys: String, CodingKey {
        case blue, green, red, timestamp
    }
}

struct RGB: Codable {
    let fps: Double
    let heartRate: Int
    let rgbValues: [RGBValue]
    
    static let rgbData: [RGB] = Bundle.main.decode(file: "hrv_data.json") ?? [] //<-- here
  //  static let sampleData: RGB = rgbData[0]  // <-- not here
}

extension Bundle{
    
    func decode<T: Decodable>(file: String) -> T? { //<-- here
        guard let url = self.url(forResource: file, withExtension: nil) else {
            fatalError("Could not find (file) in the project!")
        }
        do { //<-- here
            let data = try Data(contentsOf: url)
            return try JSONDecoder().decode(T.self, from: data)
        } catch {
            print("---> error: (error)") //<-- here, important
        }
        return nil //<-- here
    }
}

struct ContentView: View {
    var body: some View {
        Text("testing")
            .onAppear {
                print("---> rgbData: (RGB.rgbData)")
            }
    }
}

    File hrv_data.json content

     [
 {
     "fps" : 0.1548667699098587,
     "heartRate" : 81,
     "rgbValues" : [
         {
             "blue" : 0,
             "green" : 0,
             "timestamp" : "22-04-2024 10:33:57",
             "red" : 0
         }
     ]
 }
 ]
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