Issue encountered with a universal utility function designed to extract JSON data from a specified URL

Question

Issue encountered with a universal utility function designed to extract JSON data from a specified URL

For a project I'm working on, I need to fetch JSON data from multiple URLs in different Views and populate various structs. To achieve this, I've created a compact yet versatile helper function.

This function can be utilized as follows:

View 1:

let call1 = Bundle.main.decode(iobrokerSection.self, from: "http://192.168.1.205:8087/get/javascript.0.Fahrzeiten.Dauer")

View 2:

let call2 = Bundle.main.decodeURL(iobrokerweather.self, from: "http://192.168.1.205:8087/get/javascript.0.Fahrzeiten.Weather")

and so forth.

The struct iobrokerSection for the first example looks like this:

struct iobrokerNumberDataPoint: Codable {
    var val: Int
    var ack: Bool
    var ts: Int
    var q: Int
    var from: String
    var user: String
    var lc: Int
    var _id: String
    var type: String
}

Below is my handy helper function:

extension Bundle {
    func decodeURL<T: Decodable>(_ type: T.Type, from urlString: String) -> T {
        guard let url = URL(string: urlString) else {
            fatalError("Placeholder for a good error message")
        }
        
        let request = URLRequest(url: url)
        
        URLSession.shared.dataTask(with: request) { data, response, error in
            guard let loaded = try? JSONDecoder().decode(T.self, from: data!) else {
                fatalError("Placeholder for a good error message")
            }
        }.resume()

        return loaded
    }
}

I am encountering a compiler message that says "Cannot convert return expression of type Bool to return Type T" at the line "return loaded" and I'm unsure how to resolve it. Any suggestions would be greatly appreciated!

json swift

Answer 1

Answer №1

In Swift, it is recommended to start the names of your structures, classes, and protocols with an uppercase letter. Additionally, you should not wait for asynchronous methods to finish in order to return a value. Instead, you can utilize a completion handler within your method. If your goal is simply to retrieve data without performing any additional actions, there is no need to use URLRequest; you can directly pass a URL to your method. It's important not to force-unwrap the returned data as it could potentially be nil. Always safely unwrap optional data and handle errors by passing them to the completion handler. Your decode method may look something like this:

extension Bundle {
    func decode<T: Decodable>(_ type: T.Type, from url: URL, completion: @escaping (T?, Error?) -> Void) {
        URLSession.shared.dataTask(with: url) { data, response, error in
            guard let data = data else {
                completion(nil, error)
                return
            }
            do {
               try completion(JSONDecoder().decode(T.self, from: data), nil)
            } catch {
                completion(nil, error)
            }
        }.resume()
    }
}

When using this method, remember to handle the asynchronous result inside the closure:

struct IOBrokerNumberDataPoint: Codable {
    var val: Int
    var ack: Bool
    var ts: Int
    var q: Int
    var from: String
    var user: String
    var lc: Int
    var id: String
    var type: String
    enum CodingKeys: String, CodingKey {
        case val, ack, ts, q, from, user, lc, id = "_id", type
    }
}

let url = URL(string: "http://192.168.1.205:8087/get/javascript.0.Fahrzeiten.Dauer")!
Bundle.main.decode(IOBrokerNumberDataPoint.self, from: url) { brokerNumberDataPoint, error in
    guard let brokerNumberDataPoint = brokerNumberDataPoint else {
        print("error", error ?? "")
        return
    }
    print("brokerNumberDataPoint", brokerNumberDataPoint)
    // Utilize brokerNumberDataPoint here
}

An alternative approach is to leverage Swift 5 Result generic enumeration.

extension Bundle {
    func decode<T: Decodable>(from url: URL, completion: @escaping (Result<T, Error>) -> Void) {
        URLSession.shared.dataTask(with: url) { data, response, error in
            guard let data = data, error == nil else {
                if let error = error { completion(.failure(error)) }
                return
            }
            do {
                try completion(.success(JSONDecoder().decode(T.self, from: data)))
            } catch {
                completion(.failure(error))
            }

        }.resume()
    }
}

Usage:

let url = URL(string: "http://192.168.1.205:8087/get/javascript.0.Fahrzeiten.Dauer")!

Bundle.main.decode(from: url) { (result: Result<IOBrokerNumberDataPoint, Error>) in
    switch result {
    case let .success(brokerNumberDataPoint):
        print("brokerNumberDataPoint", brokerNumberDataPoint)
        // Use brokerNumberDataPoint here
    case let .failure(error):
        print("error:", error)
    }
    
    
}

Answer 2

In Swift, it is recommended to start the names of your structures, classes, and protocols with an uppercase letter. Additionally, you should not wait for asynchronous methods to finish in order to return a value. Instead, you can utilize a completion handler within your method. If your goal is simply to retrieve data without performing any additional actions, there is no need to use URLRequest; you can directly pass a URL to your method. It's important not to force-unwrap the returned data as it could potentially be nil. Always safely unwrap optional data and handle errors by passing them to the completion handler. Your decode method may look something like this:

extension Bundle {
    func decode<T: Decodable>(_ type: T.Type, from url: URL, completion: @escaping (T?, Error?) -> Void) {
        URLSession.shared.dataTask(with: url) { data, response, error in
            guard let data = data else {
                completion(nil, error)
                return
            }
            do {
               try completion(JSONDecoder().decode(T.self, from: data), nil)
            } catch {
                completion(nil, error)
            }
        }.resume()
    }
}

When using this method, remember to handle the asynchronous result inside the closure:

struct IOBrokerNumberDataPoint: Codable {
    var val: Int
    var ack: Bool
    var ts: Int
    var q: Int
    var from: String
    var user: String
    var lc: Int
    var id: String
    var type: String
    enum CodingKeys: String, CodingKey {
        case val, ack, ts, q, from, user, lc, id = "_id", type
    }
}

let url = URL(string: "http://192.168.1.205:8087/get/javascript.0.Fahrzeiten.Dauer")!
Bundle.main.decode(IOBrokerNumberDataPoint.self, from: url) { brokerNumberDataPoint, error in
    guard let brokerNumberDataPoint = brokerNumberDataPoint else {
        print("error", error ?? "")
        return
    }
    print("brokerNumberDataPoint", brokerNumberDataPoint)
    // Utilize brokerNumberDataPoint here
}

An alternative approach is to leverage Swift 5 Result generic enumeration.

extension Bundle {
    func decode<T: Decodable>(from url: URL, completion: @escaping (Result<T, Error>) -> Void) {
        URLSession.shared.dataTask(with: url) { data, response, error in
            guard let data = data, error == nil else {
                if let error = error { completion(.failure(error)) }
                return
            }
            do {
                try completion(.success(JSONDecoder().decode(T.self, from: data)))
            } catch {
                completion(.failure(error))
            }

        }.resume()
    }
}

Usage:

let url = URL(string: "http://192.168.1.205:8087/get/javascript.0.Fahrzeiten.Dauer")!

Bundle.main.decode(from: url) { (result: Result<IOBrokerNumberDataPoint, Error>) in
    switch result {
    case let .success(brokerNumberDataPoint):
        print("brokerNumberDataPoint", brokerNumberDataPoint)
        // Use brokerNumberDataPoint here
    case let .failure(error):
        print("error:", error)
    }
    
    
}

Issue encountered with a universal utility function designed to extract JSON data from a specified URL

Answer №1

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