CODEWITHSUNDEEP
swiftnetwork-programmingerror-handlingcompletionhandlerurlsession
Fabio
Fabio

Reputation: 62

Displaying networking error message to user in Swift

The question is how can I make this code reusable especially the error checking in the network method and the condition in the completionhandler, so I don't have duplicate code?

I created a method which makes a network request with URLSession and calls a completion handler with the statuscode as argument. In the completion handling, I created a condition which shows an error message or perfom a segue based on the statuscode. All of this code works but I want to make it reusable so I don't have duplicate code.

Networking method:

func saveMessage(data: String, day: String, completion: @escaping (Int)->()) {
    let url = URL(string: "\(Constants.baseURL)/daily_mindset/today_message")
    guard let requestUrl = url else { fatalError() }
    var request = URLRequest(url: requestUrl)
    request.httpMethod = "POST"
    
    // Set HTTP Request Header
    request.setValue("application/json", forHTTPHeaderField: "Accept")
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    
    let jsonData = encodeJSON(with: data, day: day)
    request.httpBody = jsonData
    
    let task = URLSession.shared.dataTask(with: request) { (data, response, error) in
        if error != nil {
            completion(700)
            return
        }
        
        guard let response = response as? HTTPURLResponse else {
            completion(701)
            return
        }

        guard (200...299).contains(response.statusCode) else {
            completion(response.statusCode)
            return
        }
        
        guard let mime = response.mimeType, mime == "application/json" else {
            completion(702)
            return
        }
        
        guard let data = data else {
            completion(703)
            return
        }
        
        do {
            let todoItemModel = try JSONDecoder().decode(MessageData.self, from: data)
            Constants.currentMindsetId = todoItemModel._id!
            print("Response data:\n \(todoItemModel)")
        } catch let jsonErr{
            print(jsonErr)
        }
        completion(response.statusCode)
    }
    task.resume()
}

Calling networking method with completionhandler:

messageManager.saveMessage(data: textView.text, day: day, completion: {(statusCode: Int) -> Void in
                    if (200...299).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.performSegue(withIdentifier: "ToDailyMindsetScreen", sender: sender)
                        }
                    } else if (400...499).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.errorLabel.text = "Please make sure you filled in the all the required fields."
                        }
                    } else if (500...599).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.errorLabel.text = "Sorry, couldn't reach our server."
                        }
                    } else if (700...).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.errorLabel.text = "Sorry, something went wrong. Try again later."
                        }
                    }
            })

Code in the networking method I want to reuse:

if error != nil {
            completion(700)
            return
        }
        
        guard let response = response as? HTTPURLResponse else {
            completion(701)
            return
        }

        guard (200...299).contains(response.statusCode) else {
            completion(response.statusCode)
            return
        }
        
        guard let mime = response.mimeType, mime == "application/json" else {
            completion(702)
            return
        }
        
        guard let data = data else {
            completion(703)
            return
        }

Code in the completionhandler I want to reuse:

if (200...299).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.performSegue(withIdentifier: "ToDailyMindsetScreen", sender: sender)
                        }
                    } else if (400...499).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.errorLabel.text = "Please make sure you filled in the all the required fields."
                        }
                    } else if (500...599).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.errorLabel.text = "Sorry, couldn't reach our server."
                        }
                    } else if (700...).contains(statusCode) {
                        DispatchQueue.main.async {
                            self.errorLabel.text = "Sorry, something went wrong. Try again later."
                        }
                    }

Upvotes: 1

Views: 2060

Answers (1)

mgapinski
mgapinski

Reputation: 483

If the error messages are ViewController specific you can start with creating a function that returns the message based on the status code like this:

private func getErrorMessageFor(statusCode: Int) -> String? {
    if (200...299).contains(statusCode) {
        //If no error message is returned assume that the request was a success
        return nil
    } else if (400...499).contains(statusCode) {
        return "Please make sure you filled in the all the required fields."
    } else if (500...599).contains(statusCode) {
        return "Sorry, couldn't reach our server."
    } else if (700...).contains(statusCode) {
        return "Sorry, something went wrong. Try again later."
    } else {
        return "Message for other errors?"
    }
}

You can always move this code to a ViewController subclass to provide more generic error messages and override it later to provide more detailed errors for a specific View Controller.

class BaseViewController: UIViewController {
    func getErrorMessageFor(statusCode: Int) -> String? {
        //base implementation here
    }
}

class OtherViewController: BaseViewController {
    override func getErrorMessageFor(statusCode: Int) -> String? {
        //create a new error message only for statusCode 404
        if statusCode == 404 {
            return "The requested resource was not found on the server. Please contact the support team"
        } else {
            return super.getErrorMessageFor(statusCode: statusCode)
        }
    } 
}

Keep in mind that as your app grows you might want to create an APIClient that would handle networking and error handling for you. Take a look at https://bustoutsolutions.github.io/siesta/, it is very user friendly

Upvotes: 1

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