I retrieved values from Json, i print retrieved values order changed(position changed) every time. please check my below code once:
override func viewDidLoad() {
super.viewDidLoad()
var myIds = [104016, 104010, 104014, 104018, 104000, 104038, 104015, 104011, 104015, 104010, 104010, 104010, 104003, 104003, 104011]
for arr in 0 ..< myIds.count-1 {
let url = URL(string: "http://.........\(myIds[arr])")
print("myIds[\(arr)]:\(myIds[arr])")
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil
{
print ("ERROR")
}
else
{
if let content = data
{
do
{
//Array
let myJson = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject
var i = myJson["Job_title_name"]!
var ist = ""
// print("i=\(i)")
ist = String(describing: i!)
print("myIds[\(arr)]=\(ist)")
}
catch
{
}
}
}
}
task.resume()
}
}
**output:**
myIds[0]:104016
myIds[1]:104010
myIds[2]:104014
myIds[3]:104018
myIds[4]:104000
myIds[5]:104038
myIds[6]:104015
myIds[7]:104011
myIds[8]:104015
myIds[9]:104010
myIds[10]:104010
myIds[11]:104010
myIds[12]:104003
myIds[13]:104003
myIds[0]=WebLogic Admin
myIds[3]=OracleDevloper
myIds[2]=Node Js Developer
myIds[1]=Angular Developer
myIds[6]=HTML&CSS Developer
myIds[5]=Senior Manager
myIds[7]=CRM Developer
myIds[4]=Windows Manager
myIds[8]=HTML&CSS Developer
myIds[9]=Angular Developer
myIds[11]=Angular Developer
myIds[10]=Angular Developer
myIds[12]=java developer
myIds[13]=java developer
This output is changed every time, when stop and run the app. but i'm unable to find the problem. please check my code once.
Required output:
myIds[0]:104016
myIds[1]:104010
myIds[2]:104014
myIds[3]:104018
myIds[4]:104000
myIds[5]:104038
myIds[6]:104015
myIds[7]:104011
myIds[8]:104015
myIds[9]:104010
myIds[10]:104010
myIds[11]:104010
myIds[12]:104003
myIds[13]:104003
myIds[0]=WebLogic Admin
myIds[1]=Angular Developer
myIds[2]=Node Js Developer
myIds[3]=OracleDevloper
myIds[4]=Windows Manager
myIds[5]=Senior Manager
myIds[6]=HTML&CSS Developer
myIds[7]=CRM Developer
myIds[8]=HTML&CSS Developer
myIds[9]=Angular Developer
myIds[10]=Angular Developer
myIds[11]=Angular Developer
myIds[12]=java developer
myIds[13]=java developer
i want the above output. In the above code whats my mistake.
URLSession.shared.dataTask() usually call API in parallel execution so no matter if calling request order will same as response order.
If you want to call request and get response in same order then you should create NSOperation queue and make dependency on it.
Network requests run asynchronously, so this is the expected behaviour. The requests don't finish in the same order as they were started.
If you need your requests to run sequentially, you can run them using DispatchGroups, but this will lead to slower performance due to the fact that your asynchronous requests are executed sequentially instead of in parallel. A better solution is to store the results in a data structure, where you can identify the objects based on a unique identifier other than their index. For your current problem, the best solution is to store the results in a dictionary, where the key is the id and the value is the value from the network request.
Concurrent solution using a Dictionary to store the output values:
override func viewDidLoad() {
super.viewDidLoad()
var myIds = [104016, 104010, 104014, 104018, 104000, 104038, 104015, 104011, 104015, 104010, 104010, 104010, 104003, 104003, 104011]
var jobTitles = [Int:String]()
let group = DispatchGroup()
for arr in 0 ..< myIds.count-1 {
let url = URL(string: "http://.........\(myIds[arr])")
print("myIds[\(arr)]:\(myIds[arr])")
group.enter()
let task = URLSession.shared.dataTask(with: url!) { (data, response, error) in
if error != nil{
print ("ERROR")
} else {
if let content = data{
do {
guard let myJson = try JSONSerialization.jsonObject(with: content, options: []) as? [String:Any] else {return}
guard let jobTitle = myJson["Job_title_name"] as? String else {return}
jobTitles[myIds[arr]] = jobTitle
group.leave()
} catch {
}
}
}
}
task.resume()
}
}
}
group.notify(queue: DispatchQueue.main, execute: {
print(jobTitles)
})
Some general advice: don't force unwrap values from a server response and don't use String(describing:) to create a String. Use optional binding or default values to safely unwrap the optionals and either cast your values to String if they are String values or just use String(value) for values from which Strings can be directly initialized (such as Int).
Related
I am facing an issue when trying to retrieve and decode JSON data from an API. I am able to get the data from the API and decode it successfully, but I can't access it from outside the function scope. I am using the following function to get and decode data. The API returns an array of JSON objects.
func getJSON(completed: #escaping () -> ()) {
var jsonData = [API_data] () // A struct for retrieved data
let url = "URL Here" // I have the original URL here, which I can't share
let task = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: { [self]data,response,error in
guard let data = data, error == nil else{
print("error")
return
}
do{
jsonData = try JSONDecoder().decode([API_data].self,from:data)
} catch{
print(error)
}
print(jsonData[0].id) // This prints my data
})
print(jsonData[0].id) // This won't print my data
task.resume()
}
struct API_data: Codable {
let id : String
}
As a result of this, I cannot use this data anywhere in the application. Any help will be appreciated. I have also tried making jsonData a global variable, updating it in the function and returning it and then using it, still doesn't work.
Thanks for your help.
As you already have a completion handler use it and pass the received data
func getJSON(completed: #escaping ([API_data]) -> Void) {
let url = "URL Here" // I have the original URL here, which I can't shar
let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, _ , error in
if let error = error { print(error); return }
do {
completed(try JSONDecoder().decode([API_data].self,from:data!))
} catch{
print(error)
}
}
task.resume()
}
and use it
getJSON { apiData in
print(apiData[0].id) // This prints my data
}
Or more comfortable with the Result type
func getJSON(completed: #escaping (Result<[API_data],Error>) -> Void) {
let url = "URL Here" // I have the original URL here, which I can't shar
let task = URLSession.shared.dataTask(with: URL(string: url)!) { data, _ , error in
if let error = error { completed(.failure(error)); return }
Result { try JSONDecoder().decode([API_data].self,from: data!) }
}
task.resume()
}
getJSON { result in
switch result {
case .success(let apiData): print(apiData[0].id) // This prints my data
case .failure(let error): print(error)
}
}
It is asynchronous, you might want to access it a bit later when it’s ready, e.g. by using the completion handler.
Try creating a completion handler from your API function and send the data with the completion. And try using it there.
I have a List that is updated with a Fetch class, an ObservableObject. It has an init function. This is that Fetch class.
#Published private(set) var items: [ItemsResult] = []
init() {
let url = URL(string: "[redacted]")!
URLSession.shared.dataTask(with: url) {(data, response, error) in
do {
if let itemsData = data {
let decodedData = try JSONDecoder().decode([ItemsResult].self, from: itemsData)
DispatchQueue.global(qos: .utility).async {
DispatchQueue.main.async {
print("running task")
self.items = decodedData
}
}
print(self.items)
} else {
print("No data")
}
} catch {
print("Error: \(error)")
}
}.resume()
}
When the app is build, it correctly displays the data returned by the API and it matches the database. However when I tap / click on one in order to delete it, or use the textarea I've added to add a new item it doesn't update.
struct TickrApp: View {
#EnvironmentObject var fetch: Fetch
var body: some View {
NavigationView {
Form {
Section {
VStack(alignment: .center) {
Text("Welcome to Tickr")
}
}
Section {
List(fetch.items) { item in
CheckView(checked: item.done, title: item.content.replacingOccurrences(of:"_", with: " "))
}
}
AddItemView()
}.navigationBarTitle(Text("Tickr"))
}
}
}
The database is being updated as shown when I log the decodedData they respond, however in each I just call Fetch(). Requests are made the same in all three cases.
One of the calls, for text input.
func toggle() {
checked = !checked
let url = URL(string: "")!
var req = URLRequest(url: url)
req.httpMethod = "POST"
let task = URLSession.shared.dataTask(with: req) { data, response, error in
guard let _ = data,
let response = response as? HTTPURLResponse,
error == nil else {
print("error", error ?? "Unknown error")
return
}
guard (200 ... 299) ~= response.statusCode else {
print("statusCode should be 2xx, but is \(response.statusCode)")
print("response = \(response)")
return
}
}
task.resume()
Fetch()
In order to update the list visually I need to completely quit the app / rerun it in order to have the new and/or deleted items show correctly. No errors show about background publishing changes or anything.
It appears that you're trying to call Fetch() to refresh your data. There are two things that are going to be a problem with this:
You're calling it outside of the dataTask completion handler. That means that it may get called before the write finishes
Calling Fetch() just creates a new instance of Fetch, when what you really want to do is update the results on your existing instance.
I'm assuming that your first code snipped is from Fetch. I'd change it to look more like this:
class Fetch: ObservableObject {
#Published private(set) var items: [ItemsResult] = []
init() {
performFetch()
}
func performFetch() {
//your existing fetch code that was in `init`
}
}
Then, in your AddItemView and CheckView, make sure you have this line:
#EnvironmentObject var fetch: Fetch
This will ensure you're using the same instance of Fetch so your list will reflect the same collection of results.
Once you're done with an operation like toggle(), call self.fetch.performFetch() to update your results. So, your last code snippet would turn into something like this:
let task = URLSession.shared.dataTask(with: req) { data, response, error in
//guard statements to check for errors
self.fetch.performFetch() //perform your refresh on the *existing* `Fetch` instance
}
A bigger refactor would involve moving your async code (like toggle) to a view model, instead of doing any of it in a View code. Also, look into using the URLSession Publishers using Combine, since you're using SwiftUI: https://developer.apple.com/documentation/foundation/urlsession/processing_url_session_data_task_results_with_combine
As a part of teaching myself Swift, I am working on a Weather App. I am currently attempting to integrate weather alerts. I use a struct called AlertData to initialize data returned from the API call to weather.gov after serializing the returned data from an API call. Or, at least that is the plan. I have modeled my classes off of other classes that request data from weather.gov, but to get an alert, I need to be able to send variable parameters in my dataTask. I use the URL extension from Apple's App Development with Swift (code below) and have the code set to issue the parameters with the users current location to get alerts where the user is currently.
My problem comes when I attempt to construct the API call to weather.gov in my AlertDataController class(code below). Xcode keeps throwing different errors and I am not sure why. I would like to use a guard statement as I have in my code below, but that throws an error of "Cannot force unwrap value of non-optional type '[[String : Any]]'" in my code where shown. It also throws the same error when I make it a simple constant assignment after unwrapping as the extension returns an optional URL.
The same code works flawlessly when I construct the URL from a string in the guard statement directly as in:
guard let url = URL(string: (baseURL + locationString + stations)) else {
What am I missing? Where my error is thrown is inside the dataTask, and regardless of how it got there, the variable url is an unwrapped URL. Thanks in advance.
Controller class:
import Foundation
import CoreLocation
struct AlertDataController {
func checkWxAlert(location: CLLocation, completion: #escaping (AlertData?) -> Void) {
let baseURL = URL(string: "https://api.weather.gov/alert")!
let locationString = "\(location.coordinate.latitude),\(location.coordinate.longitude)"
var query = [
"active": "1",
"point": locationString
]
guard let url = baseURL.withQueries(query) else {
completion(nil)
print("Unable to build URL in AlertDataController.checkWxAlert with supplied queries.")
return
}
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if let data = data,
let rawJSON = try? JSONSerialization.jsonObject(with: data),
let json = rawJSON as? [String: Any],
let featuresDict = json["features"] as? [[String: Any]],
let propertiesArray = featuresDict!["properties"] as? [String: Any] {
Error: Cannot force unwrap value of non-optional type '[[String : Any]]'
let alertData = AlertData(json: propertiesArray)
completion(alertData)
} else {
print("Either no data was returned in AlertDataController.checkWxAlert, or data was not serialized.")
completion(nil)
return
}
}
task.resume()
}
}
URL extension:
import Foundation
extension URL {
func withQueries(_ queries: [String: String]) -> URL? {
var components = URLComponents(url: self, resolvingAgainstBaseURL: true)
components?.queryItems = queries.flatMap { URLQueryItem(name: $0.0, value: $0.1) }
return components?.url
}
func withHTTPS() -> URL? {
var components = URLComponents(url: self, resolvingAgainstBaseURL: true)
components?.scheme = "https"
return components?.url
}
}
If featuresDict is really an array, you cannot use featuresDict["properties"] syntax. That subscript with string syntax is only for dictionaries. But you've apparently got an array of dictionaries.
You could iterate through the featuresDict array (which I'll rename to featuresArray to avoid confusion), you could do that after you finish unwrapping it. Or, if just want an array of the values associated with the properties key for each of those dictionaries, then flatMap is probably a good choice.
For example:
let task = URLSession.shared.dataTask(with: url) { data, _, error in
guard let data = data,
error == nil,
let json = (try? JSONSerialization.jsonObject(with: data)) as? [String: Any],
let featuresArray = json["features"] as? [[String: Any]] else {
print("Either no data was returned in AlertDataController.checkWxAlert, or data was not serialized.")
completion(nil)
return
}
let propertiesArray = featuresArray.flatMap { $0["properties"] }
let alertData = AlertData(json: propertiesArray)
completion(alertData)
}
Or, if AlertData is expecting each of those properties to be, themselves, a dictionary, you might do:
let propertiesArray = featuresArray.flatMap { $0["properties"] as? [String: Any] }
Just replace that cast with whatever type your AlertData is expecting in its array, json.
Or, if you're only interested in the first property, you'd use first rather than flatMap.
The error
Cannot force unwrap value of non-optional type '[[String : Any]]'
is very clear. It occurs because in the optional binding expression featuresDict is already unwrapped when the next condition is evaluated.
Just remove the exclamation mark
... let propertiesArray = featuresDict["properties"] as? [String: Any] {
The error is not related at all to the way the URL is created.
I am making an application which makes a lot of requests from an API. So I don't want to copy and past the code over and over. I was wondering how I can reuse my code in a some more efficient way? Maybe with extensions?
This is my code know:
func apiRequest() {
let config = URLSessionConfiguration.default
let username = "****"
let password = "****"
let loginString = String(format: "%#:%#", username, password)
let userPasswordData = loginString.data(using: String.Encoding.utf8)
let base64EncodedCredential = userPasswordData?.base64EncodedString()
let authString = "Basic " + (base64EncodedCredential)!
print(authString)
config.httpAdditionalHeaders = ["Authorization" : authString]
let session = URLSession(configuration: config)
var running = false
let urlProjects = NSURL(string: "https://start.jamespro.nl/v4/api/json/projects/?limit=10")
let task = session.dataTask(with: urlProjects! as URL) {
( data, response, error) in
if let taskHeader = response as? HTTPURLResponse {
print(taskHeader.statusCode)
}
if error != nil {
print("There is an error!!!")
print(error)
} else {
if let content = data {
do {
let dictionary = try JSONSerialization.jsonObject(with: content) as! [String:Any]
print(dictionary)
if let items = dictionary["items"] as? [[String:Any]] {
for item in items {
if let description = item["Description"] as? String {
self.projectNaam.append(description)
}
if let id = item["Id"] as? String {
self.projectId.append(id)
}
if let companyId = item["CompanyId"] as? String {
self.companyId.append(companyId)
}
}
}
self.apiRequestCompani()
}
catch {
print("Error: Could not get any data")
}
}
}
running = false
}
running = true
task.resume()
while running {
print("waiting...")
sleep(1)
}
}
Yes, you can use Extensions to create a BaseViewController and extend that where you want to use your code over and over again. Then you should abstract all dynamic data over input parameters to that method.
import UIKit
class BaseViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
}
func getApiRequest (Parameters) {
//API Request
}
And then in your view controller you just extend BaseViewController
class ViewController: BaseViewController {
override func viewDidLoad() {
super.viewDidLoad()
//Call method in baseviewcontroller
getApiRequest(parameters)
//Call method in self
self.getApiRequest(parameters)
}
override func getApiRequest(Parameters) {
//IF you need to override default configuration
}
So I don't want to copy and past the code over and over.
Absolutely right, no one aiming to get duplicated code; That's the issue of massive view controller. This issue appears since the view controller layer in your application handles most of the responsibilities, such as: getting data from the network, how data should be represented, deliver the formatted data to the view layer, etc...
There are many approaches for solving such an issue (using an appropriate architectural pattern for your application), for simplicity, I would recommend to apply the MVC-N (or MVCNetworking) approach into your app, it is almost the same usual MVC, with a separated files (managers), represent a new layer for handling -for instance- the integration with the external APIs.
Applying the MVN-N should not be that complex, nevertheless it needs to be described well (which might be too abroad to be descried in the answer), I would suggest to check the above mentioned apple example, also watching this video should be useful.
I've searched for how to do this but something just isn't making sense for me and I can't do it. All I need to do is get data out of my json session (if thats what you call it). I started programming about 3 weeks ago so I need lay mans terms please. I realize this is probably going to get marked as a duplicate but most of the answers on this / related topics are for other languages and I barely understand swift so they don't help me much.
I've spent hours trying to find the answer and since I'm new I don't know if what I'm searching for is even the right thing to be searching for. I've also tried reading the iOS developer library but either I don't understand what it's telling me or I haven't found the right section because I still can't figure this out. Please try to explain this instead of sending me to read other resources.
here is my function
func parseData() {
let urlString = "http://heroesjson.com/heroes.json"
let session = NSURLSession.sharedSession()
let url = NSURL(string: urlString)!
session.dataTaskWithURL(url) { (data: NSData?, response:NSURLResponse?, error: NSError?) -> Void in
guard let responseData = data else { return }
var json: [[String: AnyObject]]!
do {
json = try NSJSONSerialization.JSONObjectWithData(responseData, options: NSJSONReadingOptions.AllowFragments) as! [[String: AnyObject]]
}
catch {
//handle error
}
var arrayToReturn = [Hero]()
for element in json {
let hero = Hero(fromDictionary: element as! [String: AnyObject])
arrayToReturn.append(hero)
}
}.resume()//Closes Session.dataTaskWithURL
} //Closes parseData()
the goal is to get the json variable in my do statement so I can parse it outside of the function or get my "arrayToReturn" so I can save it to a global variable that I use.
If I understand correctly I can't just assign the value (arrayToReturn) to my global variable (heroes) because this is an asynchronous request so it just returns nil because the command is called before the request is finished. I think I have to use a completion handler or callback function. I don't really understand the difference between them and don't understand how or where to implement them.
Also, I don't understand this code very much either, I just know it's necessary to get what I want.
session.dataTaskWithURL(url) { (data: NSData?, response:NSURLResponse?, error: NSError?) -> Void in
"(data: NSData?, response:NSURLResponse?, error: NSError?)" looks like parameters but they don't seem to be attached to a function so that doesn't make sense to me
"-> Void" Doesn't make sense to me because -> means return whatever follows, but void indicates to me that its returning nothing, so why not just leave it out all together?
"-> Void in" What what is the significance of in here? what does it mean / signal?
Go and read about Swift Closures. To use a value outside of it, you'd need to pass it to another closure.
func parseData(callback: (heroes: [Hero]) -> Void) {
let urlString = "http://heroesjson.com/heroes.json"
let session = NSURLSession.sharedSession()
let url = NSURL(string: urlString)!
session.dataTaskWithURL(url) { (data: NSData?, response:NSURLResponse?, error: NSError?) -> Void in
guard let responseData = data else { return }
var json: [[String: AnyObject]]!
do {
json = try NSJSONSerialization.JSONObjectWithData(responseData, options: NSJSONReadingOptions.AllowFragments) as! [[String: AnyObject]]
}
catch {
//handle error
}
var arrayToReturn = [Hero]()
for element in json {
let hero = Hero(fromDictionary: element as! [String: AnyObject])
arrayToReturn.append(hero)
}
callback(heroes: arrayToReturn)
}.resume()//Closes Session.dataTaskWithURL
} //Closes parseData()
And you'd call it:
parseData { heroes in
// do something with the array
}