So I am downloading a JSON file using a URLRequest().
I parse through it in order to get a specific string and I want to set the text of a label I have in my ViewController to that specific string.
I use a CompletionHandler in order to retrieve the function that gets the JSON file from another Swift file.
Here is the code of calling the function and setting the label:
class SecondViewController: UIViewController {
tr = TransportServices()
tr.getLyftData(origin: originstring, destination: destinationstring){ json in
//Parsing JSON in order to get specific data
self.lyftlabel.text = stringexample
}
}
and here is the code of getting the JSON
func getLyftData(origin: String, destination: String, completionHandler: #escaping ([String: Any]) -> ()){
let urlrequest = URLRequest(url: URL(string: urlstring)!)
let config = URLSessionConfiguration.default
let sessions = URLSession(configuration: config)
let task = sessions.dataTask(with: urlrequest) {(data, response, error) in
guard error == nil else {
print(error!)
return
}
guard let responseData = data else {
print("error, did not receive data")
return
}
do {
if let json = try JSONSerialization.jsonObject(with: responseData, options: []) as? [String: Any]{
completionHandler(json)
}
}
catch {
print("Error with URL Request")
}
}
task.resume()
}
This does the job, but in a very slow manner. I know that there is a runtime issue because UILabel.text must be set from main thread only, but I don't know any other way to fix it. Please help.
If you want to set label text in main thread use this:
DispatchQueue.main.async {
self.lyftlabel.text = stringexample
}
Related
I have a JSON request that gets data from the Darksky API, I get the data properly and it is showing on the screen. However, When i'm trying to set the data from the array I get from the JSON call in another array, it stays empty.
This is my code:
just declaring the array:
var mForecastArray = [Weather]()
this is the function that calls the API:
func getForecast(){
Weather.forecast(withLocation: "37.8267,-122.4233") { (arr) in
DispatchQueue.main.async {
self.mForecastArray = arr
self.mTodayWeather = arr[0]
self.mCollectionView.reloadData()
}
}
}
The weird part is that it does work, and the data do shows on screen, but still, mForecastArray seems null.
This is the API call itself:
static func forecast(withLocation location: String, completion: #escaping ([Weather]) -> ()){
let url = basePath + location
let request = URLRequest(url: URL(string: url)!)
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
var forecastArray: [Weather] = []
if let data = data{
do{
if let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String:Any]{
if let dailyForecast = json["daily"] as? [String:Any]{
if let dailyData = dailyForecast["data"] as? [[String:Any]]{
for dataPoint in dailyData{
if let weatherObject = try? Weather(json: dataPoint){
forecastArray.append(weatherObject)
}
}
}
}
}
}catch{
print(error.localizedDescription)
}
completion(forecastArray)
}
}
task.resume()
}
It's a visual asynchronous illusion.
The static method forecast works asynchronously.
Most likely your code looks like
getForecast()
print(self.mForecastArray)
This cannot work because the array is populated much later.
Move the print line into the completion handler of the static method
func getForecast(){
Weather.forecast(withLocation: "37.8267,-122.4233") { (arr) in
DispatchQueue.main.async {
self.mForecastArray = arr
print(self.mForecastArray)
self.mTodayWeather = arr[0]
self.mCollectionView.reloadData()
}
}
}
I am trying to downlod multiple JSON files with a URLSession and when I run the funtion one time it works. But the moment I call the getSMAPrices function from a loop it does not work and I can not find out why.
Here is the working download function that works if i call it.
func getSMAPrices(symbol: String) {
let urlString = "https://www.alphavantage.co/query?function=SMA&symbol=\(symbol)&interval=daily&time_period=9&series_type=close&apikey=KPLI12AW8JDXM77Y"
guard let url = URL(string: urlString) else {
return
}
dataTask = defaultSession.dataTask(with: url, completionHandler: { (data, response, error) in
if error != nil {
print(error!.localizedDescription)
}
guard let data = data else {
return
}
//Implement JSON decoding and parsing
do {
//Decode retrived data with JSONDecoder and assing type of Article object
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601
let stockData = try decoder.decode(SimpelMovingAvarage.self, from: data)
//Get back to the main queue
DispatchQueue.main.async {
print(stockData)
}
} catch let jsonError {
print(jsonError)
}
})
dataTask?.resume()
}
And here is my very simple loop that replaces a part in the URL every run cycle. But nothing happens.
public func scanSymbols() {
for symbol in self.symbols {
progress += 1
progresBar.maxValue = Double(symbols.count)
progresBar.doubleValue = progress
//This does not work
getSMAPrices(symbol: symbol.key)
}
}
It's because your dataTask variable appears to be an instance property and is getting overwritten every time you call this method.
I have this code :
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
if error != nil {
print(error!)
return
}
do {
let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
if let parseJSON = json {
let getDetail = parseJSON["detail"] as? String
returnDetail = getDetail!.base64Decoded()
} // parse json end
} // do end
catch {
print(error)
}
} // let task end
returnDetail has been defined previously. I did anything to set returnDetail value to getDetail!.base64Decoded() but it only works inside let task = ...
How can I pass it to the outer scope?
You have several methods to tackle the issue of returning a value from inside an asynchronous function. One of them is to wrap the asynchronous network call inside a function and make it return a completionHandler.
Some general advice: don't use force unwrapping unless you are 100% sure that your optional value won't be nil. With network requests, the data can be nil even if there's no error, so never force unwrap data, use safe unwrapping with if let or guard let. Don't use .mutableContainers in Swift when parsing a JSON value, since it has no effect. The mutability of the parsed JSON object is decided by using the let or var keyword to declare the variable holding it. Also don't use NSDictionary, use its native Swift counterpart, Dictionary ([String:Any] is a shorthand for the type Dictionary<String,Any>).
func getDetail(withRequest request: URLRequest, withCompletion completion: #escaping (String?, Error?) -> Void) {
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
if error != nil {
completion(nil, error)
return
}
else if let data = data {
do {
guard let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String:Any] else {completion(nil, nil);return}
guard let details = json["detail"] as? String else {completion(nil, nil);return}
completion(details, nil)
}
catch {
completion(nil, error)
}
}
}
task.resume()
}
Then you can call this function by
getDetail(withRequest: request, withCompletion: { detail, error in
if error != nil {
//handle error
} else if detail = detail {
//You can use detail here
}
})
I would suggest to use a completion handler.
func foo(withCompletion completion: (String?, Error?) -> Void) {
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
if error != nil {
completion(nil, error)
return
}
do {
let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
if let parseJSON = json {
let details = parseJSON["detail"] as? String
completion(details, nil)
} // parse json end
} // do end
catch {
completion(nil, error)
}
} // let task end
}
I think, you use CallBack(Clourse) of Swift to return data when getDetail have data.
I've created a macOS console app in swift, but the code is never executed, =I have to use Semaphore but is there another way to do this ?
my purpose is to create a method returning a json file
class test{
func gizlo(){
let config = URLSessionConfiguration.default // Session Configuration
let session = URLSession(configuration: config) // Load configuration into Session
let url = URL(string: "https://itunes.apple.com/fr/rss/topmovies/limit=25/json")!
let task = session.dataTask(with: url, completionHandler: {
(data, response, error) in
if error != nil {
print(error!.localizedDescription)
} else {
do {
if let json = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
{
print(json)
}
} catch {
print("error in JSONSerialization")
}
}
})
task.resume()
}
}
let tr=test()
tr.gizlo()
Thanks
To avoid Semaphores you can use simple readLine() that will wait for input from the keyboard. Yes it is not obvious but it is woking because it prevent terminal app from exit.
Just add in the and of the file:
_ = readLine()
As Oleg points out, putting readLine() at the end of the top-level code will prevent the program for exiting until you hit Enter in the terminal or wherever FileHandle.standardInput is pointing. That's probably fine for just testing the code quickly in the debugger or in a Playground. An infinite loop would also work, though you'd have to actually terminate it in the debugger or with kill from the command line.
The real issue is why you don't want to use a semaphore. Since they're not difficult to use, I'm going to hazard a guess that it's just because you don't want to pollute your asynchronous data task completion handler with a semaphore when you probably only need it to wait for the data for testing purposes.
Assuming my guess is correct, the real issue isn't actually using a semaphore, it's where you think you need to put them. As David Wheeler once said, "Any problem can be solved by adding a layer of indirection."
You don't want the semaphore explicitly in the completion handler you pass to dataTask. So one solution would be to make gizlo accept a completion handler of its own, and then create a method that calls gizlo with a closure that handles the semaphore. That way you can decouple the two and even add some flexibility for other uses. I've modified your code to do that:
import Foundation
import Dispatch // <-- Added - using DispatchSemaphore
class test{
func gizlo(_ completion: ((Result<[String: Any]?, Error>) -> Void)? = nil) { // <-- Added externally provided completion handler
let config = URLSessionConfiguration.default // Session Configuration
let session = URLSession(configuration: config) // Load configuration into Session
let url = URL(string: "https://itunes.apple.com/fr/rss/topmovies/limit=25/json")!
let task = session.dataTask(with: url, completionHandler: {
(data, response, error) in
let result: Result<[String: Any]?, Error>
if let responseError = error { // <-- Changed to optional binding
print(responseError.localizedDescription)
result = .failure(responseError) // <-- Added this
} else {
do {
if let json = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
{
print(json)
result = .success(json) // <-- Added this
}
else { // <-- Added this else block
result = .success(nil)
}
} catch {
print("error in JSONSerialization")
result = .failure(error) // <-- Added this
}
}
completion?(result) // <-- Added this call
})
task.resume()
}
func blockingGizlo() throws -> [String: Any]? // <-- Added this method
{
let sem = DispatchSemaphore(value: 1)
sem.wait()
var result: Result<[String: Any]?, Error>? = nil
gizlo {
result = $0
sem.signal()
}
sem.wait() // This wait will block until the closure calls signal
sem.signal() // Release the second wait.
switch result
{
case .success(let json) : return json
case .failure(let error) : throw error
case .none: fatalError("Unreachable")
}
}
}
let tr=test()
do {
let json = try tr.blockingGizlo()
print("\(json?.description ?? "nil")")
}
catch { print("Error: \(error.localizedDescription)") }
I have access the "dictionary" moviedb for
example : https://www.themoviedb.org/search/remote/multi?query=exterminador%20do%20futuro&language=en
How can i catch only the film's name and poster from this page to my project in Swift ?
It's answer :)
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
reload()
}
private func reload() {
let requestUrl = "https://www.themoviedb.org/search/remote/multi?query=exterminador%20do%20futuro&language=en"
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config)
let request = NSURLRequest(URL: NSURL(string: requestUrl)!)
let task = session.dataTaskWithRequest(request, completionHandler: { (data, response, error) -> Void in
if let error = error {
println("###### error ######")
}
else {
if let JSON = NSJSONSerialization.JSONObjectWithData(data,
options: .AllowFragments,
error: nil) as? [NSDictionary] {
for movie in JSON {
let name = movie["name"] as! String
let posterPath = movie["poster_path"] as! String
println(name) // "Terminator Genisys"
println(posterPath) // "/5JU9ytZJyR3zmClGmVm9q4Geqbd.jpg"
}
}
}
})
task.resume()
}
}
You need to include your api key along with the request. I'd just try something like this to see if it works or not. If it does, then you can go about using the api key in a different way to make it more secure. I wouldn't bother as it's not an api with much sensitive functionality.
let query = "Terminator+second"
let url = NSURL(string: "http://api.themoviedb.org/3/search/keyword?api_key=YOURAPIKEY&query=\(query)&language=en")!
let request = NSMutableURLRequest(URL: url)
request.addValue("application/json", forHTTPHeaderField: "Accept")
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request) { data, response, error in
if let response = response, data = data {
print(response)
//DO THIS
print(String(data: data, encoding: NSUTF8StringEncoding))
//OR THIS
if let o = NSJSONSerialization.JSONObjectWithData(data, options: nil, error:nil) as? NSDictionary {
println(dict)
} else {
println("Could not read JSON dictionary")
}
} else {
print(error)
}
}
task.resume()
The response you'll get will have the full list of properties. You need the poster_path and title (or original_title) property of the returned item.