在数组为空时如何避免从API提取数据时应用崩溃

Question

I was checking my app, I tried to login and it login my account smoothly then suddenly it crashed and it shows an Fatal error: Index out of range appeared in this part of the code

completion(demographicsArray[0], nil)

Upon checking, the dumping process of the data in the back end is still on process that why the array on my end is empty, no data was pulled. How can I prevent the crashing of the app and how can I include alert message that will notify the user that their record is still on process? Please help me out been solving this for a week but still I can't solve it. Codes are below for your references. Thank you.

APIService.swift

 static func getPatientInformation(informationType: PatientInformationType, tokenType: String, token: String, hospitalNumber: String, completion: @escaping getPatientInformationTaskCompletion<Any>) {

        var patientInformationURL: URL!

        switch informationType {
            case .allergies:
                patientInformationURL = URL(string: "\(Endpoint.Patient.allergies)?hn=\(hospitalNumber)")
            case .demographics:
                patientInformationURL = URL(string: "\(Endpoint.Patient.demographics)?hn=\(hospitalNumber)")
            case .diagnosis:
                patientInformationURL = URL(string: "\(Endpoint.Patient.diagnosis)?hn=\(hospitalNumber)")
            case .medications:
                patientInformationURL = URL(string: "\(Endpoint.Patient.medications)?hn=\(hospitalNumber)")
        }

        guard patientInformationURL != nil else {
            completion(nil, .invalidURL)
            return
        }

        let header: HTTPHeaders = [
            "Authorization": "\(tokenType) \(token)",
            "Accept": "application/json"
        ]

        Alamofire.request(patientInformationURL, headers: header).responseJSON(completionHandler: { (response) in
            guard HelperMethods.reachability(responseResult: response.result) else {
                completion(nil, .noNetwork)
                return
            }

            guard let statusCode = response.response?.statusCode else {
                completion(nil, .noStatusCode)
                return
            }

            switch(statusCode) {
            case 200:
                guard let jsonData = response.data else {
                    completion(nil, .invalidJSON)

                    return
                }

                let decoder = JSONDecoder()

                switch (informationType) {
                case .allergies:
                    do {
                        let allergyArray = try decoder.decode([Allergies].self, from: jsonData)
                        completion(allergyArray, nil)
                    }catch {
                        completion(nil, .invalidJSON)
                    }
                case .demographics:
                    do {
                        let demographicsArray = try decoder.decode([Demographics].self, from: jsonData)
                            completion(demographicsArray.first, nil)
                        }catch {
                            completion(nil, .invalidJSON)
                    }

                case .diagnosis:
                    do {
                        let diagnosisArray = try decoder.decode([Diagnosis].self, from: jsonData)
                        completion(diagnosisArray, nil)
                    }catch {
                        completion(nil, .invalidJSON)
                    }
                case .medications:
                    do {
                        let medicationArray = try decoder.decode([Medication].self, from: jsonData)
                        completion(medicationArray, nil)
                    }catch {
                        completion(nil, .invalidJSON)
                    }
                }
            case 401:
                completion(nil, .unauthorizedToken)
            default:
                print("UNCAPTURED STATUS CODE FROM getPatientInformation\nSTATUS CODE: \(statusCode)")
                completion(nil, .uncapturedStatusCode)
            }
        })
    }

PatientProfileViewController.swift

func getPatientInfo() {
    guard let username = KeychainManager.getUsername(),
        let tokenType = KeychainManager.getTokenType(),
        let token = KeychainManager.getToken() else { return }

    SVProgressHUD.setDefaultMaskType(.black)
    SVProgressHUD.show(withStatus: "Retrieving Patient Information")

    APIService.Patients.getPatientInformation(informationType: .demographics,
                                              tokenType: tokenType, token: token,
                                              hospitalNumber: username) { (demographics, error) in

        guard let patientInformation = demographics as? Demographics, error == nil else {
            if let networkError = error {
                switch networkError {
                    case .noNetwork:
                        let popupDialog = PopupDialog(title: "No Network", message: "\(networkError.rawValue)")
                        popupDialog.addButton(DefaultButton(title: "OK", action: nil))
                        self.present(popupDialog, animated: true, completion: nil)
                    default:
                        let popupDialog = PopupDialog(title: "Error", message: "There is something went wrong. Please try again")
                        popupDialog.addButton(DefaultButton(title: "OK", action: nil))
                        self.present(popupDialog, animated: true, completion: nil)
                }
            }

            SVProgressHUD.dismiss()
            return
        }



        self.patientDemographics = patientInformation

        self.welcomeLabel.text = self.patientDemographics.displayName ?? "Welcome"

        self.patientInformationTableView.reloadData()
        SVProgressHUD.dismiss()
    }
}

Answer 1

You can always check if the array has enough elements before accessing it.

if demographicsArray.count > 0 {
    completion(demographicsArray[0], nil)
} else {
    // handle empty array completion
}

Note: Why is your database returning data before processing it?

Answer 2

I prefer use "guard" instead of "if"

guard demographicsArray.count > 0 else {
  completion(nil, .noDemographicsAtPosition)
}

completion(resonseToSend, nil)

I think this way is more readable.

Advise: getPatientInformation has a lot of responsibilities, it would be great if you divide it into others functions like:

func getPatientInformationURL() -> String
func processResponse(completion: @escaping getPatientInformationTaskCompletion<Any>)

probably it became your code more readable, hope it helps you.