I have created a utility class in my Swift project that handles all the REST requests and responses. I have built a simple REST API so I can test my code. I have created a class method that needs to return an NSArray but because the API call is async I need to return from the method inside the async call. The problem is the async returns void.
If I were doing this in Node I would use JS promises but I can't figure out a solution that works in Swift.
import Foundation
class Bookshop {
class func getGenres() -> NSArray {
println("Hello inside getGenres")
let urlPath = "http://creative.coventry.ac.uk/~bookshop/v1.1/index.php/genre/list"
println(urlPath)
let url: NSURL = NSURL(string: urlPath)
let session = NSURLSession.sharedSession()
var resultsArray:NSArray!
let task = session.dataTaskWithURL(url, completionHandler: {data, response, error -> Void in
println("Task completed")
if(error) {
println(error.localizedDescription)
}
var err: NSError?
var options:NSJSONReadingOptions = NSJSONReadingOptions.MutableContainers
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: options, error: &err) as NSDictionary
if(err != nil) {
println("JSON Error \(err!.localizedDescription)")
}
//NSLog("jsonResults %#", jsonResult)
let results: NSArray = jsonResult["genres"] as NSArray
NSLog("jsonResults %#", results)
resultsArray = results
return resultsArray // error [anyObject] is not a subType of 'Void'
})
task.resume()
//return "Hello World!"
// I want to return the NSArray...
}
}
You can pass callback, and call callback inside async call
something like:
class func getGenres(completionHandler: (genres: NSArray) -> ()) {
...
let task = session.dataTaskWithURL(url) {
data, response, error in
...
resultsArray = results
completionHandler(genres: resultsArray)
}
...
task.resume()
}
and then call this method:
override func viewDidLoad() {
Bookshop.getGenres {
genres in
println("View Controller: \(genres)")
}
}
Introduced in Swift 5.5 (iOS 15, macOS 12), we would now use the async-await pattern:
func fetchGenres() async throws -> [Genre] {
…
let (data, _) = try await URLSession.shared.dataTask(for: request)
return try JSONDecoder().decode([Genre].self, from: data)
}
And we would call it like:
let genres = try await fetchGenres()
The async-await syntax is far more concise and natural than the traditional completion handler pattern outlined in my original answer, below.
For more information, see Meet async/await in Swift.
The historic pattern is to use completion handlers closure.
For example, we would often use Result:
func fetchGenres(completion: #escaping (Result<[Genre], Error>) -> Void) {
...
URLSession.shared.dataTask(with: request) { data, _, error in
if let error = error {
DispatchQueue.main.async {
completion(.failure(error))
}
return
}
// parse response here
let results = ...
DispatchQueue.main.async {
completion(.success(results))
}
}.resume()
}
And you’d call it like so:
fetchGenres { results in
switch results {
case .failure(let error):
print(error.localizedDescription)
case .success(let genres):
// use `genres` here, e.g. update model and UI
}
}
// but don’t try to use `genres` here, as the above runs asynchronously
Note, above I’m dispatching the completion handler back to the main queue to simplify model and UI updates. Some developers take exception to this practice and either use whatever queue URLSession used or use their own queue (requiring the caller to manually synchronize the results themselves).
But that’s not material here. The key issue is the use of completion handler to specify the block of code to be run when the asynchronous request is done.
Note, above I retired the use of NSArray (we don’t use those bridged Objective-C types any more). I assume that we had a Genre type and we presumably used JSONDecoder, rather than JSONSerialization, to decode it. But this question didn’t have enough information about the underlying JSON to get into the details here, so I omitted that to avoid clouding the core issue, the use of closures as completion handlers.
Swiftz already offers Future, which is the basic building block of a Promise. A Future is a Promise that cannot fail (all terms here are based on the Scala interpretation, where a Promise is a Monad).
https://github.com/maxpow4h/swiftz/blob/master/swiftz/Future.swift
Hopefully will expand to a full Scala-style Promise eventually (I may write it myself at some point; I'm sure other PRs would be welcome; it's not that difficult with Future already in place).
In your particular case, I would probably create a Result<[Book]> (based on Alexandros Salazar's version of Result). Then your method signature would be:
class func fetchGenres() -> Future<Result<[Book]>> {
Notes
I do not recommend prefixing functions with get in Swift. It will break certain kinds of interoperability with ObjC.
I recommend parsing all the way down to a Book object before returning your results as a Future. There are several ways this system can fail, and it's much more convenient if you check for all of those things before wrapping them up into a Future. Getting to [Book] is much better for the rest of your Swift code than handing around an NSArray.
Swift 4.0
For async Request-Response you can use completion handler. See below I have modified the solution with completion handle paradigm.
func getGenres(_ completion: #escaping (NSArray) -> ()) {
let urlPath = "http://creative.coventry.ac.uk/~bookshop/v1.1/index.php/genre/list"
print(urlPath)
guard let url = URL(string: urlPath) else { return }
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do {
if let jsonResult = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.mutableContainers) as? NSDictionary {
let results = jsonResult["genres"] as! NSArray
print(results)
completion(results)
}
} catch {
//Catch Error here...
}
}
task.resume()
}
You can call this function as below:
getGenres { (array) in
// Do operation with array
}
Swift 3 version of #Alexey Globchastyy's answer:
class func getGenres(completionHandler: #escaping (genres: NSArray) -> ()) {
...
let task = session.dataTask(with:url) {
data, response, error in
...
resultsArray = results
completionHandler(genres: resultsArray)
}
...
task.resume()
}
Swift 5.5, async/wait-based solution
The original test URL provided by the original poster is no longer functional, so I had to change things a bit. This solution is based on a jokes API I found. That API returns a single joke, but I return it as an array of String ([String]), to keep it as consistent as possible with the original post.
class Bookshop {
class func getGenres() async -> [String] {
print("Hello inside getGenres")
let urlPath = "https://geek-jokes.sameerkumar.website/api?format=json"
print(urlPath)
let url = URL(string: urlPath)!
let session = URLSession.shared
typealias Continuation = CheckedContinuation<[String], Never>
let genres = await withCheckedContinuation { (continuation: Continuation) in
let task = session.dataTask(with: url) { data, response, error in
print("Task completed")
var result: [String] = []
defer {
continuation.resume(returning: result)
}
if let error = error {
print(error.localizedDescription)
return
}
guard let data = data else {
return
}
do {
let jsonResult = try JSONSerialization.jsonObject(with: data, options: [.mutableContainers])
print("jsonResult is \(jsonResult)")
if let joke = (jsonResult as? [String: String])?["joke"] {
result = [joke]
}
} catch {
print("JSON Error \(error.localizedDescription)")
print("data was \(String(describing: String(data: data, encoding: .utf8)))")
return
}
}
task.resume()
}
return genres
}
}
async {
let final = await Bookshop.getGenres()
print("Final is \(final)")
}
The withCheckedContinuation is how you made the Swift async function actually run in a separate task/thread.
I hope you're not still stuck on this, but the short answer is that you can't do this in Swift.
An alternative approach would be to return a callback that will provide the data you need as soon as it is ready.
There are 3 ways of creating call back functions namely:
1. Completion handler
2. Notification
3. Delegates
Completion Handler
Inside set of block is executed and returned when source is available, Handler will wait until response comes so that UI can be updated after.
Notification
Bunch of information is triggered over all the app, Listner can retrieve n make use of that info. Async way of getting info through out the project.
Delegates
Set of methods will get triggered when delegate is been called, Source must be provided via methods itself
Swift 5.5:
TL;DR: Swift 5.5 is not yet released(at the time of writing). To use swift 5.5, download swift toolchain development snapshot from here and add compiler flag -Xfrontend -enable-experimental-concurrency. Read more here
This can be achieved easily with async/await feature.
To do so, you should mark your function as async then do the operation inside withUnsafeThrowingContinuation block like following.
class Bookshop {
class func getGenres() async throws -> NSArray {
print("Hello inside getGenres")
let urlPath = "http://creative.coventry.ac.uk/~bookshop/v1.1/index.php/genre/list"
print(urlPath)
let url = URL(string: urlPath)!
let session = URLSession.shared
return try await withUnsafeThrowingContinuation { continuation in
let task = session.dataTask(with: url, completionHandler: {data, response, error -> Void in
print("Task completed")
if(error != nil) {
print(error!.localizedDescription)
continuation.resume(throwing: error!)
return
}
do {
let jsonResult = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [String: Any]
let results: NSArray = jsonResult!["genres"] as! NSArray
continuation.resume(returning: results)
} catch {
continuation.resume(throwing: error)
}
})
task.resume()
}
}
}
And you can call this function like
#asyncHandler
func check() {
do {
let genres = try await Bookshop.getGenres()
print("Result: \(genres)")
} catch {
print("Error: \(error)")
}
}
Keep in mind that, when calling Bookshop.getGenres method, the caller method should be either async or marked as #asyncHandler
self.urlSession.dataTask(with: request, completionHandler: { (data, response, error) in
self.endNetworkActivity()
var responseError: Error? = error
// handle http response status
if let httpResponse = response as? HTTPURLResponse {
if httpResponse.statusCode > 299 , httpResponse.statusCode != 422 {
responseError = NSError.errorForHTTPStatus(httpResponse.statusCode)
}
}
var apiResponse: Response
if let _ = responseError {
apiResponse = Response(request, response as? HTTPURLResponse, responseError!)
self.logError(apiResponse.error!, request: request)
// Handle if access token is invalid
if let nsError: NSError = responseError as NSError? , nsError.code == 401 {
DispatchQueue.main.async {
apiResponse = Response(request, response as? HTTPURLResponse, data!)
let message = apiResponse.message()
// Unautorized access
// User logout
return
}
}
else if let nsError: NSError = responseError as NSError? , nsError.code == 503 {
DispatchQueue.main.async {
apiResponse = Response(request, response as? HTTPURLResponse, data!)
let message = apiResponse.message()
// Down time
// Server is currently down due to some maintenance
return
}
}
} else {
apiResponse = Response(request, response as? HTTPURLResponse, data!)
self.logResponse(data!, forRequest: request)
}
self.removeRequestedURL(request.url!)
DispatchQueue.main.async(execute: { () -> Void in
completionHandler(apiResponse)
})
}).resume()
There are mainly 3 ways of achieving callback in swift
Closures/Completion handler
Delegates
Notifications
Observers can also be used to get notified once the async task has been completed.
There are some very generic requirements that would like every good API Manager to satisfy:
will implement a protocol-oriented API Client.
APIClient Initial Interface
protocol APIClient {
func send(_ request: APIRequest,
completion: #escaping (APIResponse?, Error?) -> Void)
}
protocol APIRequest: Encodable {
var resourceName: String { get }
}
protocol APIResponse: Decodable {
}
Now Please check complete api structure
// ******* This is API Call Class *****
public typealias ResultCallback<Value> = (Result<Value, Error>) -> Void
/// Implementation of a generic-based API client
public class APIClient {
private let baseEndpointUrl = URL(string: "irl")!
private let session = URLSession(configuration: .default)
public init() {
}
/// Sends a request to servers, calling the completion method when finished
public func send<T: APIRequest>(_ request: T, completion: #escaping ResultCallback<DataContainer<T.Response>>) {
let endpoint = self.endpoint(for: request)
let task = session.dataTask(with: URLRequest(url: endpoint)) { data, response, error in
if let data = data {
do {
// Decode the top level response, and look up the decoded response to see
// if it's a success or a failure
let apiResponse = try JSONDecoder().decode(APIResponse<T.Response>.self, from: data)
if let dataContainer = apiResponse.data {
completion(.success(dataContainer))
} else if let message = apiResponse.message {
completion(.failure(APIError.server(message: message)))
} else {
completion(.failure(APIError.decoding))
}
} catch {
completion(.failure(error))
}
} else if let error = error {
completion(.failure(error))
}
}
task.resume()
}
/// Encodes a URL based on the given request
/// Everything needed for a public request to api servers is encoded directly in this URL
private func endpoint<T: APIRequest>(for request: T) -> URL {
guard let baseUrl = URL(string: request.resourceName, relativeTo: baseEndpointUrl) else {
fatalError("Bad resourceName: \(request.resourceName)")
}
var components = URLComponents(url: baseUrl, resolvingAgainstBaseURL: true)!
// Common query items needed for all api requests
let timestamp = "\(Date().timeIntervalSince1970)"
let hash = "\(timestamp)"
let commonQueryItems = [
URLQueryItem(name: "ts", value: timestamp),
URLQueryItem(name: "hash", value: hash),
URLQueryItem(name: "apikey", value: "")
]
// Custom query items needed for this specific request
let customQueryItems: [URLQueryItem]
do {
customQueryItems = try URLQueryItemEncoder.encode(request)
} catch {
fatalError("Wrong parameters: \(error)")
}
components.queryItems = commonQueryItems + customQueryItems
// Construct the final URL with all the previous data
return components.url!
}
}
// ****** API Request Encodable Protocol *****
public protocol APIRequest: Encodable {
/// Response (will be wrapped with a DataContainer)
associatedtype Response: Decodable
/// Endpoint for this request (the last part of the URL)
var resourceName: String { get }
}
// ****** This Results type Data Container Struct ******
public struct DataContainer<Results: Decodable>: Decodable {
public let offset: Int
public let limit: Int
public let total: Int
public let count: Int
public let results: Results
}
// ***** API Errro Enum ****
public enum APIError: Error {
case encoding
case decoding
case server(message: String)
}
// ****** API Response Struct ******
public struct APIResponse<Response: Decodable>: Decodable {
/// Whether it was ok or not
public let status: String?
/// Message that usually gives more information about some error
public let message: String?
/// Requested data
public let data: DataContainer<Response>?
}
// ***** URL Query Encoder OR JSON Encoder *****
enum URLQueryItemEncoder {
static func encode<T: Encodable>(_ encodable: T) throws -> [URLQueryItem] {
let parametersData = try JSONEncoder().encode(encodable)
let parameters = try JSONDecoder().decode([String: HTTPParam].self, from: parametersData)
return parameters.map { URLQueryItem(name: $0, value: $1.description) }
}
}
// ****** HTTP Pamater Conversion Enum *****
enum HTTPParam: CustomStringConvertible, Decodable {
case string(String)
case bool(Bool)
case int(Int)
case double(Double)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let string = try? container.decode(String.self) {
self = .string(string)
} else if let bool = try? container.decode(Bool.self) {
self = .bool(bool)
} else if let int = try? container.decode(Int.self) {
self = .int(int)
} else if let double = try? container.decode(Double.self) {
self = .double(double)
} else {
throw APIError.decoding
}
}
var description: String {
switch self {
case .string(let string):
return string
case .bool(let bool):
return String(describing: bool)
case .int(let int):
return String(describing: int)
case .double(let double):
return String(describing: double)
}
}
}
/// **** This is your API Request Endpoint Method in Struct *****
public struct GetCharacters: APIRequest {
public typealias Response = [MyCharacter]
public var resourceName: String {
return "characters"
}
// Parameters
public let name: String?
public let nameStartsWith: String?
public let limit: Int?
public let offset: Int?
// Note that nil parameters will not be used
public init(name: String? = nil,
nameStartsWith: String? = nil,
limit: Int? = nil,
offset: Int? = nil) {
self.name = name
self.nameStartsWith = nameStartsWith
self.limit = limit
self.offset = offset
}
}
// *** This is Model for Above Api endpoint method ****
public struct MyCharacter: Decodable {
public let id: Int
public let name: String?
public let description: String?
}
// ***** These below line you used to call any api call in your controller or view model ****
func viewDidLoad() {
let apiClient = APIClient()
// A simple request with no parameters
apiClient.send(GetCharacters()) { response in
response.map { dataContainer in
print(dataContainer.results)
}
}
}
This is a small use case that might be helpful:-
func testUrlSession(urlStr:String, completionHandler: #escaping ((String) -> Void)) {
let url = URL(string: urlStr)!
let task = URLSession.shared.dataTask(with: url){(data, response, error) in
guard let data = data else { return }
if let strContent = String(data: data, encoding: .utf8) {
completionHandler(strContent)
}
}
task.resume()
}
While calling the function:-
testUrlSession(urlStr: "YOUR-URL") { (value) in
print("Your string value ::- \(value)")
}
I have some basics in Swift, and I'm now trying to learn iOS development. I'm currently working in a small app that will ask resource on an API I've made that returns json made from :
struct A : Codable {
let name: String
let age: Int
}
struct B : Codable {
let something: String
}
Both API and app have these structs defined. As I'm always querying the same API, I thought of wrapping the part that ask the API some resources and decode this so I have an instance of the struct to use in my callback. Here's this method :
static func getContent(urlRequest: URLRequest, decodable: Decodable, completion: #escaping (Codable?, ErrorEnum?)->Void) {
let config = URLSessionConfiguration.default
let session = URLSession(configuration: config)
let task = session.dataTask(with: urlRequest) {
data, response, error in
guard let data = data else {
completion(nil, .noData) // Handling errors in an enum
return
}
let decoder = JSONDecoder()
if let full = try? decoder.decode(decodable, from: data) {
completion(full, nil)
}
}
task.resume()
}
My problem concerns the decodable param. This shows an error and prevent me from compiling the app. After finding some resources on StackOverflow, I tried to change the parameters as
static func getContent(urlRequest: URLRequest, decodable: Decodable.Type, completion: #escaping (Codable?, ErrorEnum?)->Void)
I also tried to keep the parameter like this, and instead change inside the decode params
if let full = try? decoder.decode(decodable, from: data) {
completion(full, nil)
}
but nothing seems to satisfy the compiler... And looking at decode method inside Swift source code didn't help me that much as it requires T.Type where T is Decodable
My wish is to be able to use this as follow :
static func getA() {
guard let url = URL(string: "http://localhost/a") else { return }
let urlRequest = URLRequest(url: url)
getContent(urlRequest: urlRequest, decodable: A.self) {
a, error in
guard a = a else { return }
print(a.name!)
}
}
Do you have any idea how I could achieve this ? I also don't really know how to call this type of parameters or what to search on google that can lead me to the answer (lack of vocabulary).
Thank you !
try this just add a generic .Type of Codable and use its type as a parameter to pass foo.self
static func getContent<T: Codable>(urlRequest: URLRequest, decodable: T.Type, completion: #escaping (T?, ErrorEnum?)->Void) {
let config = URLSessionConfiguration.default
let session = URLSession(configuration: config)
let task = session.dataTask(with: urlRequest) {
data, response, error in
guard let data = data else {
completion(nil, .noData) // Handling errors in an enum
return
}
let decoder = JSONDecoder()
if let full = try? decoder.decode(decodable, from: data) {
completion(full, nil)
}
}
task.resume()
}
You can use this:
func genericRequest<T: Decodable>(_ request: URLRequest, completion: #escaping APIGenericRequestCompletion<T>) {
Alamofire.request(request).responseData { (response) in
guard let data = response.data else {
completion(nil)
return
}
do {
let decodedObject = try JSONDecoder().decode(T.self, from: data)
completion(decodedObject)
} catch {
completion(nil)
}
}
}
where APIGenericRequestCompletion is:
typealias APIGenericRequestCompletion<T: Decodable> = (_ result: T?) -> Void
Then you use it as:
genericRequest(request) { (decodableObjectResponse) in
// your code here
}
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 have a function that is build to get the latest items from a API. There are several other ones, with different functionality, but they all work the same. It looks like this:
func getLatest(pageNumber: Int) -> Array<Any>{
let urlRequest = URL(string: baseUrl + latestUrl + String(pageNumber))
let requestedData = doRequest(url: urlRequest!, completion: { data -> Void in
// We have the data from doRequest stored in data, but now what?!
})
return allData
}
I also have a async method that handles the requests. That one looks like this:
func doRequest(url: URL, completion: #escaping ([[ApiItem]]) -> ()){
var allItems = [[ApiItem]]()
URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do{
let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as! [String: AnyObject]
let results = json["items"] as? [AnyObject]
for r in results!{
let item = ApiItem(json: r as! [String: Any])
allItems.append([item])
}
completion(allItems)
} catch let jsonError{
print("JSON error: \(jsonError)")
}
}.resume()
The doRequest function works absolutely fine. It gets the data, parses the JSON and send it back to getLatest --> requestedData. The problem right now is, is that getLatest() is a function that needs to return the data that is stored in the data variable of requestedData.
How can I make it so, that the getLatest() function returns the data that is stored in the data in requestedData()?
So I've fixed it by doing this:
In the first method, the one that actually needs the data from the API, I added this:
let trendingData = restApiManager.getLatest(pageNumber: 0, completion: { data -> Void in
let item = data[indexPath.row]
let url = NSURL(string: item.still)
let data = NSData(contentsOf: url as! URL)
if data != nil {
cell.image.image = UIImage(data:data! as Data)
}
})
The getLatest() method looks like this:
func getLatest(pageNumber: Int, completion: #escaping ([ApiItem]) -> ()) {
let urlRequest = URL(string: baseUrl + trendingUrl + String(pageNumber))
let requestedData = doRequest(url: urlRequest!, completion: { data -> Void in
// We have the data from doRequest stored in data
var requestedData = data
completion(requestedData)
})
}
And finally, the doRequest() method looks like this:
func doRequest(url: URL, completion: #escaping ([ApiItem]) -> ()){
var allItems = [ApiItem]()
URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let data = data else { return }
do{
let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as! [String: AnyObject]
let results = json["items"] as? [AnyObject]
for r in results!{
let item = ApiItem(json: r as! [String: Any])
allItems.append(item)
}
completion(allItems)
} catch let jsonError{
print("JSON error: \(jsonError)")
}
}.resume()
}
What I would do is use a Singleton in which I can store the Data
class DataManager:NSObject
{
static let instance = DataManager()
override private init(){}
var items:[ApiItem] = []
}
Then in your first method I would do this:
func getLatest(pageNumber: Int){
let urlRequest = URL(string: baseUrl + latestUrl + String(pageNumber))
let requestedData = doRequest(url: urlRequest!, completion: { data -> items in
// We have the data from doRequest stored in data, but now what?!
DataManager.instance.items = items
})
}
This is how I usually go about this kind of situations. There may be better options though...
I am calling Openweather map API using Swift and from the response I need to return a particular value as string.
However when I try to return the value error comes as JSON is not convertible to string.
func callWeatherServ(name:String, completion:(Dictionary<String,AnyObject>) -> Void)
{
var baseUrl: String = "http://api.openweathermap.org/data/2.5/weather"
var url: String = "\(baseUrl)?q=\(name)"
let finalUrl: NSURL = NSURL(string: url)!
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(finalUrl, completionHandler: {data, response, error -> Void in
if error != nil
{
// If there is an error in the web request, print it to the console
println(error.localizedDescription)
}
var err: NSError?
var jsonResult = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: &err) as! NSDictionary
if err != nil
{
// If there is an error parsing JSON, print it to the console
println("JSON Error \(err!.localizedDescription)")
}
let json = JSON(jsonResult)
println("response is \(json) ")
var weathername = json["weather"][0]["main"]
if (weathername != nil)
{
return weathername
}
})
task.resume()
}
I get that since we have used closure whose return type void so we should use completion handler. But I am not aware how we can do that.
Also how we can call the function if we pass completion handler as parameter?
If you want to keep using SwiftyJSON as in your example, here's how to do it:
change the type of the completion handler from a dictionary to the JSON type used by SwiftyJSON.
then wrap the value you want to "return" in the handler.
then call your method as in my example, with a trailing closure
Swift 2
func callWeatherServ(name:String, completion:(object: JSON) -> Void) {
let baseUrl: String = "http://api.openweathermap.org/data/2.5/weather"
let url: String = "\(baseUrl)?q=\(name)"
if let finalUrl = NSURL(string: url) {
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(finalUrl, completionHandler: {data, response, error -> Void in
if let error = error {
print(error.localizedDescription)
} else {
if let data = data {
let json = JSON(data: data)
print("response is \(json) ")
completion(object: json["weather"][0]["main"])
} else {
print("No data")
}
}
})
task.resume()
}
}
Call the method:
callWeatherServ("paris") { (object) in
// here you get back your JSON object
print(object)
}
Note that you were parsing your data twice, with NSJSONSerialization and with SwiftyJSON, so I've removed the unnecessary NSJSONSerialization part.
Original Swift 1 version
func callWeatherServ(name:String, completion:(object: JSON) -> Void)
{
var baseUrl: String = "http://api.openweathermap.org/data/2.5/weather"
var url: String = "\(baseUrl)?q=\(name)"
let finalUrl: NSURL = NSURL(string: url)!
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(finalUrl, completionHandler: {data, response, error -> Void in
if error != nil
{
// If there is an error in the web request, print it to the console
println(error.localizedDescription)
}
var err: NSError?
let json = JSON(data: data, options: NSJSONReadingOptions.allZeros, error: &err)
println("response is \(json) ")
var weathername = json["weather"][0]["main"]
if (weathername != nil)
{
completion(object: weathername)
}
})
task.resume()
}
Call the method:
callWeatherServ("paris", completion: { (object) -> Void in
println(object) // "Clear"
})
Implement completion handler from where you are calling this method and use the string at that place only no need to return the string.
You can directly use it from the completion handle by implemet it in caller function