I have a method for GET request in my code:
func makeHTTPGetRequest(path: String, parameters: [String: AnyObject], completionHandler: (NSData?, NSURLResponse?, NSError?) -> Void) -> NSURLSessionTask {
let parameterString = parameters.stringFromHttpParameters()
let requestURL = NSURL(string:"\(path)?\(parameterString)")!
let request = NSMutableURLRequest(URL: requestURL)
request.HTTPMethod = "GET"
request.setValue("Bearer " + userInfoDefaults.stringForKey("accessToken")!, forHTTPHeaderField: "Authorization")
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request, completionHandler:completionHandler)
task.resume()
return task
}
That is called by an another method that populates a picker view on a specific scene:
func getAffiliateds() -> [String]? {
var affiliateds:[String] = []
makeHTTPGetRequest(baseURL + "affiliateds", parameters: [:], completionHandler: { (data, response, error) in
do {
affiliateds = try NSJSONSerialization.JSONObjectWithData(data!, options:[]) as! [String]
print (affiliateds)
}
catch { print("Error: \(error)") }
})
return affiliateds
}
I need to get all affiliateds from my webservice and then list it on the picker view. But when I debugged the code I noticed that affiliateds are first returned as a null array and then it is returned with the correct information. I need to return the array from getAffiliateds only when it has already received the data from the webservice. How can I make this?
You can't. Your getAffiliateds() cannot return a value dependent on the asynchronous code that it will run. That is the nature of asynchronous code. Instead, perform a callback of some sort in the completion handler when it is called:
makeHTTPGetRequest(baseURL + "affiliateds", parameters: [:], completionHandler: { (data, response, error) in
do {
affiliateds = try NSJSONSerialization.JSONObjectWithData(data!, options:[]) as! [String]
print (affiliateds)
// DO SOMETHING HERE
}
}
A frequent strategy is for the caller to provide another completion handler which this completion handler will call.
You have a routine:
func getAffiliateds() -> [String]? {
var affiliateds:[String] = []
makeHTTPGetRequest(baseURL + "affiliateds", parameters: [:], completionHandler: { (data, response, error) in
do {
affiliateds = try NSJSONSerialization.JSONObjectWithData(data!, options:[]) as! [String]
print (affiliateds)
}
catch { print("Error: \(error)") }
})
return affiliateds
}
And you presumably have some code that does something like:
func populatePicklist() {
let affiliateds = getAffiliateds()
// populate picklist here
}
You should change this to:
func getAffiliatedsWithCompletionHandler(completionHandler: ([String]?) -> ()) {
makeHTTPGetRequest(baseURL + "affiliateds", parameters: [:]) { data, response, error in
do {
let affiliateds = try NSJSONSerialization.JSONObjectWithData(data!, options:[]) as? [String] // two notes here: first, define local var here, not up above; second, use `as?` to gracefully handle problems where result was not `[String]`
print (affiliateds)
completionHandler(affiliateds)
}
catch {
print("Error: \(error)")
completionHandler(nil)
}
}
}
func populatePicklist() {
getAffiliatedsWithCompletionHandler { affiliateds in
// populate picklist here
}
// but not here
}
Related
I am starting to use RxSwift to make the service call.
This was my old code:
class Service: GraphQLService {
func graphQL(body: [String: Any?], onSuccess: #escaping (Foundation.Data) throws -> (), onFailure: #escaping (Error) -> ()) {
guard let urlValue = Bundle.main.urlValue else { return }
guard let url = URL(string: urlValue) else { return
print("Error with info.plist")
}
var request = URLRequest(url: url)
let userKey = Bundle.main.userKeyValue
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue(userKey, forHTTPHeaderField: "userid")
request.httpBody = try? JSONSerialization.data(withJSONObject: body, options: .fragmentsAllowed)
URLSession.shared.dataTask(with: request) { (data, response, error) in
if let error = error {
onFailure(error)
}
if let data = data {
do{
try onSuccess(data)
}
catch{
onFailure(error)
}
}
}.resume()
}
And here I do the function to get time deposits:
final class TimeDepositManager: Service, TimeDepositManagerProtocol {
let timeDepositQuery = Bundle.main.queryValue
func getTimeDeposits(onSuccess: #escaping ([TimeDeposits]) -> (), onFailure: #escaping (Error) -> ()) {
let body = ["query": timeDepositQuery]
Service().graphQL(body: body, onSuccess: { data in
let json = try? JSONDecoder().decode(GraphQLResponse.self, from: data)
onSuccess(json?.data?.account?.timeDeposits ?? [])
}, onFailure: onFailure)
}
And so far this is my code with RxSwift:
class Service: GraphQLService {
func graphQL(body: [String : Any?]) -> Observable<Foundation.Data> {
return Observable.create { observer in
let urlValue = Bundle.main.urlValue
let url = URL(string: urlValue ?? "")
let session = URLSession.shared
var request = URLRequest(url: url!)
let userKey = Bundle.main.userKeyValue
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue(userKey, forHTTPHeaderField: "userid")
request.httpBody = try? JSONSerialization.data(withJSONObject: body, options: .fragmentsAllowed)
session.dataTask(with: request) { (data, response, error) in
if let error = error {
observer.onError(error)
}
if let data = data {
do{
try onSuccess(data)
observer.onNext(data)
}
catch{
//onFailure(error)
observer.onError(error)
print("Error: \(error.localizedDescription)")
}
}
}.resume()
return Disposables.create {
session.finishTasksAndInvalidate()
}
}
}
This is where I don't understand how in my getTimeDeposits () I can do the deserialization with try? JSONDecoder () ... with RxSwift without using onSuccess?
final class TimeDepositManager: Service, TimeDepositManagerProtocol {
let timeDepositQuery = Bundle.main.queryValue
func getTimeDeposits() -> Observable<[TimeDeposits]> {
let body = ["query": timeDepositQuery]
Service().graphQL(body: body)
}
You can have getTimeDeposits() return an Observable as well and handle the deserialization in a map closure. A couple of other things.
RxCocoa already has a method on URLSession so you don't need to write your own.
I suggest reducing the amount of code you have in a function that makes the network request. You want to be able to test your logic for making the request without actually making it.
Something like this:
final class TimeDepositManager: Service, TimeDepositManagerProtocol {
let timeDepositQuery = Bundle.main.queryValue
func getTimeDeposits() -> Observable<[TimeDeposits]> {
let body = ["query": timeDepositQuery]
return Service().graphQL(body: body)
.map { try JSONDecoder().decode(GraphQLResponse.self, from: $0).data?.account?.timeDeposits ?? [] }
}
}
class Service: GraphQLService {
func graphQL(body: [String: Any?]) -> Observable<Data> {
guard let urlValue = Bundle.main.urlValue else { fatalError("Error with info.plist") }
let request = urlRequest(urlValue: urlValue, body: body)
return URLSession.shared.rx.data(request: request) // this is in RxCocoa
}
func urlRequest(urlValue: String, body: [String: Any?]) -> URLRequest {
guard let url = URL(string: urlValue) else { fatalError("Error with urlValue") }
var request = URLRequest(url: url)
let userKey = Bundle.main.userKeyValue
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.setValue(userKey, forHTTPHeaderField: "userid")
request.httpBody = try? JSONSerialization.data(withJSONObject: body, options: .fragmentsAllowed)
return request
}
}
If you don't want to use RxCocoa for some reason, here is the correct way to wrap the URLSession.dataTask method:
extension URLSession {
func data(request: URLRequest) -> Observable<Data> {
Observable.create { observer in
let task = self.dataTask(with: request, completionHandler: { data, response, error in
guard let response = response as? HTTPURLResponse else {
observer.onError(URLError.notHTTPResponse(data: data, response: response))
return
}
guard 200 <= response.statusCode && response.statusCode < 300 else {
observer.onError(URLError.failedResponse(data: data, response: response))
return
}
guard let data = data else {
observer.onError(error ?? RxError.unknown)
return
}
observer.onNext(data)
observer.onCompleted() // be sure to call `onCompleted()` when you are done emitting values.
// make sure every possible path through the code calls some method on `observer`.
})
return Disposables.create { task.cancel() } // don't forget to handle cancelation properly. You don't want to kill *all* tasks, just this one.
}
}
}
enum URLError: Error {
case notHTTPResponse(data: Data?, response: URLResponse?)
case failedResponse(data: Data?, response: HTTPURLResponse)
}
I have a function that sends a GET request to an API and I need to wait for the response before I can continue with the rest of my code.
I have tried various different threads but haven't got it to work. I've been trying to solve this by myself but I am quite confused by threads and so fourth.
These are my functions:
func checkDomains() {
let endings = [".com"]
for ending in endings {
let domainName = names[randomNameIndx] + ending
let urlString = "https://domainr.p.mashape.com/v2/status?mashape-key={my-key}" + domainName
let url = URL(string: urlString)
var request = URLRequest(url: url!)
request.setValue("{my-key}", forHTTPHeaderField: "X-Mashape-Key")
request.setValue("application/json", forHTTPHeaderField: "Accept")
request.httpMethod = "GET"
var ourBool = false
DispatchQueue.main.sync {
let task = URLSession.shared.dataTask(with: request, completionHandler: { (data, response, er) in
do {
print("hey")
if let json = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? NSDictionary {
ourBool = String(describing: json).contains("inactive")
if ourBool {
self.domainStatuses.append("available")
} else {
self.domainStatuses.append("taken")
}
}
} catch {
}
})
task.resume()
}
}
}
#objc func btnTapped(sender: UIButton) {
self.prepareForNewName()
sender.shake(direction: "horizontal", swings: 1)
self.checkDomains() // This needs to finish before calling the next functions
self.setupForNewName()
self.animateForNewName()
}
My suggestion is in adding callback param into your async function. Example below:
func checkDomains(_ onResult: #escaping (Error?) -> Void)
Then you can call onResult inside your function in places where server return success result or error.
func checkDomains(_ onResult: #escaping (Error?) -> Void) {
...
let task = URLSession.shared.dataTask ... {
do {
//Parse response
DispatchQueue.main.async { onResult(nil) }
} catch {
DispatchQueue.main.async { onResult(error) }
}
...
}
}
The last thing you need pass callback param in place where you calling checkDomains function
#objc func btnTapped(sender: UIButton) {
self.prepareForNewName()
sender.shake(direction: "horizontal", swings: 1)
self.checkDomains { [unowned self] error in
if let error = error {
// handle error
return
}
self.setupForNewName()
self.animateForNewName()
}
}
Thank you for your answers. I just came home and realized there is a simpler way of doing this.
let task = URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in
do {
...
if response != nil {
DispatchQueue.main.async {
self.setupForNewName()
self.animateForNewName()
}
}
}
} catch {
print(error)
}
})
task.resume()
Of course this is dependent on the response of the API but I am confident enough the API will always respond.
Lately it is a good practice to do network call asynchronously. There some technics to make code simpler, like https://cocoapods.org/pods/ResultPromises
TBC...
So we have this function that retrieves JSON data and presents it in its completion block, what I'm trying to understand is why use the signature: ((Data) -> Void) instead of just (Data), is the void really necessary? Here is the function:
typealias JSONData = ((Data) -> Void)
func getJSONData(type: String, urlExtension: String, completion: #escaping JSONData) {
let request = URLRequest(url: URL(string:"\(baseURL)\(type)/\(urlExtension)?api_key=\(apiKey)®ion=US&append_to_response=videos,images,releases")! )
let dataTask = session.dataTask(with: request, completionHandler: { (data, response, error) in
if error == nil {
if let httpResponse = response as? HTTPURLResponse {
switch (httpResponse.statusCode) {
case 200:
if let data = data {
completion(data)
}
default:
print(httpResponse.statusCode)
}
}
} else {
DispatchQueue.main.async {
if let error = error {
print("Error: \(error.localizedDescription)") }
return
}
}
})
dataTask.resume()
}
Swift syntax dictates that you must declare closures with a return type after the ->.
You have two options:
typealias JSONData = (Data) -> Void
typealias JSONData = (Data) -> ()
I see Apple using #1 most frequently.
I'm experimenting with async calls but I'm a little lost. The print(json) in the viewDidLoad outputs an empty dictionary, but the one within the function prints correctly. This is unsurprising; it gets to that print before the async is completed. I can't figure out how to fix it; I tried putting the return within the completion handler, but I got an error that Unexpected non-void return value in void function. I tried changing the completion handler to expect a return value, but either that's not the right approach or I was doing it wrong.
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let json = getJson("https://maps.googleapis.com/maps/api/geocode/json?address=WashingtonDC&sensor=false")
print(json)
}
func getJson(url: String) -> AnyObject {
var json:AnyObject = [:]
let urlPath = NSURL(string: url)
let urlRequest = NSURLRequest(URL: urlPath!)
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config)
let task = session.dataTaskWithRequest(urlRequest, completionHandler: {
(data, response, error) in
if error != nil {
print("Error")
} else {
do {
json = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers)
print(json)
} catch {
print("json error")
}
}
})
task.resume()
return json
}
}
You will need to have a completion handler based interface to your async API.
func getJson(url: String, completion : (success: Bool, json: AnyObject? ) ->Void ) -> Void {
var json:AnyObject = [:]
let urlPath = NSURL(string: url)
let urlRequest = NSURLRequest(URL: urlPath!)
let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config)
let task = session.dataTaskWithRequest(urlRequest, completionHandler: {
(data, response, error) in
if error != nil {
print("Error")
} else {
do {
json = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers)
print(json)
//Call the completion handler here:
completion(success : true, json :json )
} catch {
print("json error")
completion(success : false, json :nil )
}
}
})
task.resume()
}
}
Now you call call this API as follows-
override func viewDidLoad() {
super.viewDidLoad()
getJson("https://maps.googleapis.com/maps/api/geocode/json?address=WashingtonDC&sensor=false") { (success, json) -> Void in
if success {
if let json = json {
print(json)
}
}
}
}
I have written a function for a URL request. This contains a completion handler that returns a dictionary of [String: AnyObject] that is fetched from the URL.
The code for this is:
func getDataAsyncFromURLRequest(url: NSURL, completion: ([String : AnyObject]) -> ()) {
let request = NSMutableURLRequest(URL: url)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error != nil {
print("error=\(error)")
return
}
else {
let datastring = NSString(data: data!, encoding: NSUTF8StringEncoding)
if let data = datastring!.dataUsingEncoding(NSUTF8StringEncoding) {
do {
let json = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions()) as! [String : AnyObject]
completion(json)
} catch {
print("json error: \(error)")
}
}
}
}
task.resume()
}
In some cases, however, I will receive an array of [String : AnyObject] and not the dictionary. So instead of making a duplicate function that takes the array of dictionaries as parameter for the completion handler, I though it was possible to do like this
func getDataAsyncFromURLRequest<T>(url: NSURL, completion: (T) -> ()) {
// code here
}
... and then do like this let json = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions()) as! T, but that gives me this error: Cannot invoke 'getDataAsyncFromURLRequest' with an argument list of type '(NSURL, completion: (_) -> ())'
What would be the best way to make the completion handler accept a parameter with a type decided at runtime, if possible at all?
It's very easy why don't you use AnyObject
func getDataAsyncFromURLRequest(url: NSURL, completion: (AnyObject) -> ()) {
let request = NSMutableURLRequest(URL: url)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error != nil {
print("error=\(error)")
return
}
else {
let datastring = NSString(data: data!, encoding: NSUTF8StringEncoding)
if let data = datastring!.dataUsingEncoding(NSUTF8StringEncoding) {
do {
let json = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions())
completion(json)
} catch {
print("json error: \(error)")
}
}
}
}
task.resume()
}
And result of JSONObjectWithData can be [AnyObject] (Array) or [String:AnyObject] and tree of those items.
So after got result, you can also check type of result in completion block
Like this
if result is [String:AnyObject]
...
else if result is [AnyObject]
...
else
//throw error : because then it is not JSON