Reading local JSON file and using it to populate UITableView - json

Question

I am writing an app that needs to look at a local JSON file, then compare it's version to one I have hosted on a website. If they don't match, download the one from the web and save it locally. If they do match, then continue on and use the local JSON file. This version info is in the JSON file itself.
Previously, my app would simply parse the online data and use that directly. It would then populate the UITableView using the JSON data. Now that I am using my local file, the UITableView isn't getting populating, and I'm not certain how to fix it. From reading the new function, I think my issue is that I'm not using JSONDecoder(), and instead using JSONSerialization(), and therefore I can't point it at the specific metadata I want.
26 Jun 18 Edit (Below is my BonusListViewController.swift file):
//
// BonusListViewController.swift
// Tour of Honor
//
// Created by Tommy Craft on 6/6/18.
// Copyright © 2018 Tommy Craft. All rights reserved.
//
import UIKit
import os.log
import Foundation
class BonusListViewController: UITableViewController {
var bonuses = [JsonFile.JsonBonuses]()
let defaults = UserDefaults.standard
override func viewDidLoad() {
super.viewDidLoad()
// MARK: Data Structures
// Settings Struct
struct Constants {
struct RiderData {
let riderNumToH = "riderNumToH"
let pillionNumToH = "pillionNumToH"
}
struct RallyData {
let emailDestinationToH = "emailDestinationToH"
}
}
//MARK: Check for updated JSON file
checkJSON()
//MARK: Trigger JSON Download
/*
downloadJSON {
print("downloadJSON Method Called")
}
*/
}
// MARK: - Table View Configuration
// MARK: Table view data source
override func numberOfSections(in tableView: UITableView) -> Int {
print("Found \(bonuses.count) sections.")
return bonuses.count
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
print("Found \(bonuses.count) rows in section.")
return bonuses.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = UITableViewCell(style: .default, reuseIdentifier: nil)
cell.textLabel?.text = bonuses[indexPath.section].name.capitalized
return cell
}
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
performSegue(withIdentifier: "showDetail", sender: self)
}
// MARK: - Table View Header
override func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
return 30
}
override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
return bonuses[section].state
}
override func tableView(_ tableView: UITableView, heightForFooterInSection section: Int) -> CGFloat {
return 3
}
// MARK: Functions
// MARK: - Download JSON from ToH webserver
func downloadJSON(completed: #escaping () -> ()) {
let url = URL(string: "http://tourofhonor.com/BonusData.json")
URLSession.shared.dataTask(with: url!) { [weak self] (data, response, error) in
if error == nil {
do {
let posts = try JSONDecoder().decode(JsonFile.self, from: data!)
DispatchQueue.main.async {
completed()
}
print("Downloading Updated JSON (Version \(posts.meta.version))")
print(posts.bonuses.map {$0.bonusCode})
print(posts.bonuses.map {$0.state})
self?.bonuses = posts.bonuses
self?.defaults.set("downloadJSON", forKey: "jsonVersion") //Set version of JSON for comparison later
DispatchQueue.main.async {
//reload table in the main queue
self?.tableView.reloadData()
}
} catch {
print("JSON Download Failed")
}
}
}.resume()
}
func checkJSON() {
//MARK: Check for updated JSON file
let defaults = UserDefaults.standard
let hostedJSONFile = "http://tourofhonor.com/BonusData.json"
let jsonURL = URL(string: hostedJSONFile)
var hostedJSONVersion = ""
let jsonData = try! Data(contentsOf: jsonURL!)
let jsonFile = try! JSONSerialization.jsonObject(with: jsonData, options: .mutableContainers) as! [String : Any]
let metaData = jsonFile["meta"] as! [String : Any]
hostedJSONVersion = metaData["version"] as! String
let localJSONVersion = defaults.string(forKey: "jsonVersion")
if localJSONVersion != hostedJSONVersion {
print("L:\(localJSONVersion!) / H:\(hostedJSONVersion)")
print("Version Mismatch: Retrieving lastest JSON from server.")
updateJSONFile()
} else {
//Retrieve the existing JSON from documents directory
print("L:\(localJSONVersion!) / H:\(hostedJSONVersion)")
print("Version Match: Using local file.")
let fileURL = defaults.url(forKey: "pathForJSON")
do {
let localJSONFileData = try Data(contentsOf: fileURL!, options: [])
let myJson = try JSONSerialization.jsonObject(with: localJSONFileData, options: .mutableContainers) as! [String : Any]
//Use my downloaded JSON file to do stuff
print(myJson)
DispatchQueue.main.async {
//reload table in the main queue
self.tableView.reloadData()
}
} catch {
print(error)
}
}
}
func updateJSONFile() {
print("updateJSONFile Method Called")
let hostedJSONFile = "http://tourofhonor.com/BonusData.json"
let jsonURL = URL(string: hostedJSONFile)
let itemName = "BonusData.json"
let defaults = UserDefaults.standard
do {
let directory = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor:nil, create:false)
let fileURL = directory.appendingPathComponent(itemName)
let jsonData = try Data(contentsOf: jsonURL!)
let jsonFile = try JSONSerialization.jsonObject(with: jsonData, options: .mutableContainers) as? [String : Any]
let metaData = jsonFile!["meta"] as! [String : Any]
let jsonVersion = metaData["version"]
print("JSON VERSION ", jsonVersion!)
try jsonData.write(to: fileURL, options: .atomic)
defaults.set(fileURL, forKey: "pathForJSON") //Save the location of your JSON file to UserDefaults
defaults.set(jsonVersion, forKey: "jsonVersion") //Save the version of your JSON file to UserDefaults
DispatchQueue.main.async {
//reload table in the main queue
self.tableView.reloadData()
}
} catch {
print(error)
}
}
// MARK: - Navigation
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let destination = segue.destination as? BonusDetailViewController {
destination.bonus = bonuses[(tableView.indexPathForSelectedRow?.row)!]
}
}
}
And here is the JsonFile.swift:
import Foundation
struct JsonFile: Codable {
struct Meta: Codable {
let fileName: String
let version: String
}
struct JsonBonuses: Codable {
let bonusCode: String
let category: String
let name: String
let value: Int
let city: String
let state: String
let flavor: String
let imageName: String
}
let meta: Meta
let bonuses: [JsonBonuses]
}
Is this related to not using JSONDecoder() in my updated version or am I going down the wrong path there? Also, how do I get this new data to work with the UITableView?

Answer 1

First of all, you are parsing JSON values incorrectly. You need to first understand your JSON format. You go to your JSON file link, and analyze it. If it starts with a "{", then it is a Dictionary, if it starts with a "[", then it is an Array. In your case, it is a Dictionary, then there come the keys which are Strings ("meta", "bonuses"). So, we know our keys are Strings. Next, we look at our values. For "meta" we have a Dictionary of String : String; for "bonuses" we have an Array of Dictionaries.
So, our JSON format is [String : Any], or it can be written Dictionary<String, Any>.
Next step, is accessing those values in the Dictionary.
func updateJSONFile() {
print("updateJSONFile Method Called")
let hostedJSONFile = "http://tourofhonor.com/BonusData.json"
let jsonURL = URL(string: hostedJSONFile)
let itemName = "BonusData.json"
let defaults = UserDefaults.standard
do {
let directory = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor:nil, create:false)
let fileURL = directory.appendingPathComponent(itemName)
let jsonData = try Data(contentsOf: jsonURL!)
let jsonFile = try JSONSerialization.jsonObject(with: jsonData, options: .mutableContainers) as? [String : Any]
let metaData = jsonFile!["meta"] as! [String : Any]
let jsonVersion = metaData["version"]
print("JSON VERSION ", jsonVersion!)
try jsonData.write(to: fileURL, options: .atomic)
defaults.set(fileURL, forKey: "pathForJSON") //Save the location of your JSON file to UserDefaults
defaults.set(jsonVersion, forKey: "jsonVersion") //Save the version of your JSON file to UserDefaults
DispatchQueue.main.async {
//reload table in the main queue
self.tableView.reloadData()
}
} catch {
print(error)
}
}
Then, when you access your locally saved file, again, you have to parse the JSON to check the versions:
func checkJSON() {
//MARK: Check for updated JSON file
let defaults = UserDefaults.standard
let hostedJSONFile = "http://tourofhonor.com/BonusData.json"
let jsonURL = URL(string: hostedJSONFile)
var hostedJSONVersion = ""
let jsonData = try! Data(contentsOf: jsonURL!)
let jsonFile = try! JSONSerialization.jsonObject(with: jsonData, options: .mutableContainers) as! [String : Any]
let metaData = jsonFile["meta"] as! [String : Any]
hostedJSONVersion = metaData["version"] as! String
let localJSONVersion = defaults.string(forKey: "jsonVersion")
if localJSONVersion != hostedJSONVersion {
print("\(localJSONVersion) : \(hostedJSONVersion)")
updateJSONFile()
} else {
//Retrieve the existing JSON from documents directory
print("\(localJSONVersion) : \(hostedJSONVersion)")
print("Local JSON is still the latest version")
let fileUrl = defaults.url(forKey: "pathForJSON")
do {
let localJSONFileData = try Data(contentsOf: fileUrl!, options: [])
let myJson = try JSONSerialization.jsonObject(with: localJSONFileData, options: .mutableContainers) as! [String : Any]
//Use my downloaded JSON file to do stuff
DispatchQueue.main.async {
//reload table in the main queue
self.tableView.reloadData()
}
} catch {
print(error)
}
}
}
Don't forget to allow arbitrary loads in your Info.plist file, because your JSON file is hosted on a website without https.