What am I doing wrong? How do I get the Single from the closure?
How can I get value from Alamofire.request?
func loadImageName(url: URL) -> Single<String> {
let data = try? Data(contentsOf: url)
guard let query = data else {
return .error(Error.notFound)
}
...
return Single.deferred {
Alamofire.request(request).responseJSON {
if let error = $0.error {
return Single<String>.error(error)
}
return Single<String>.just(result)
}
}
}
In this case you'll want Single.create.
This takes a block, which has a single argument. This argument is a function that you can call to pass a SingleEvent, i.e. either a .success(Element) (where Element is String in your case) or an .error.
The block must return a Disposable. You can construct a Disposable that will do additional work when it gets disposed. In the context of network requests, it makes sense to cancel the request.
func loadImageName(url: URL) -> Single<String> {
let data = try? Data(contentsOf: url)
guard let query = data else {
return .error(Error.notFound)
}
// ...
Single.create { single in
let request = Alamofire.request(request).responseJSON {
if let error = $0.error {
return single(.error(error))
}
return single(.success(result))
}
return Disposables.create { request.cancel() }
}
}
Related
I have this function:
func makeRepoRequest() -> Single<[String: Any]> {
return Single<[String: Any]>.create {[weak self] observer in
guard let something = self?.temp else {
let disposeBag = DisposeBag()
self?.getRepo("364").subscribe(onSuccess: { content in
observer(.success(content))
}, onError: { error in
observer(.error(error))
}).disposed(by: disposeBag)
return Disposables.create()
}
observer(.success(something))
return Disposables.create()
}
}
is subscribe to this function:
func getRepo(_ repo: String) -> Single<[String: Any]> {
return Single<[String: Any]>.create { single in
print(repo)
let url = "https://api.github.com/repositories?since=\(repo)"
print(url)
let task = URLSession.shared.dataTask(with: URL(string:url)!) { data, _, error in
if let error = error {
single(.error(error))
return
}
guard let data = data,
let json = try? JSONSerialization.jsonObject(with: data, options: []),
let result = json as? [String: Any] else {
let error = NSError(domain: "Decoding", code: 0, userInfo: nil)
single(.error(error))
return
}
single(.success(result))
}
task.resume()
return Disposables.create()
}
}
but for some reason the subscription it never gets a call back. Any of you knows why the subscription never gets a call back?
I'll really appreciate your help.
Your makeRepoRequest() is defined incorrectly. The disposable you create inside the closure should be the one that you return. There shouldn't be any disposeBag in there, also you need to unwrap self and make sure something is emitted if self doesn't exist, also if you are going to keep a cache in temp you really should assign to it...
func makeRepoRequest() -> Single<[String: Any]> {
return Single<[String: Any]>.create { [weak self] observer in
guard let this = self else {
observer(.error(MyError.missingSelf))
return Disposables.create()
}
guard !this.temp.isEmpty else {
return this.getRepo("364").subscribe(onSuccess: { content in
this.temp = content
observer(.success(content))
}, onError: { error in
observer(.error(error))
})
}
observer(.success(this.temp))
return Disposables.create()
}
}
However, since you are just emitting content with no changes, you don't even need to use .create(_:). So something like this:
func makeRepoRequest() -> Single<[String: Any]> {
if !temp.isEmpty {
return getRepo("364")
.do(onSuccess: { [weak self] in self?.temp = $0 })
}
else {
return Single.just(temp)
}
}
Lastly, you aren't properly canceling your network request in your getRepo(_:) method. It should end with return Disposables.create { task.cancel() }
I suggest you read up more on Disposables.
Trying to make a program for a news site. I take information from the site through the api, everything works fine.
The only question is, how do I get this array out of the loop?
Here is my code:
import UIKit
class ViewController: UIViewController {
var news:[News] = []
override func viewDidLoad() {
super.viewDidLoad()
getUsers()
print(news)
}
func getUsers() {
guard let url = URL(string: "http://prostir.news/swift/api2.php") else {return}
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
do {
news = try JSONDecoder().decode([News].self, from: data)
// print(self.news)
} catch let error {
print(error)
}
}
}.resume()
}
}
struct News:Codable, CustomStringConvertible{
let href:String?
let site:String?
let title:String?
let time:String?
var description: String {
return "(href:- \(href), site:- \(site), title:- \(title), time:- \(time))"
}
}
Declare news array in your class and assign the response to this array in getUsers method
var news:[News] = []
func getUsers(){
guard let url = URL(string: "https") else {return}
URLSession.shared.dataTask(with: url) { data, response, error in
if let data = data {
do {
self.news = try JSONDecoder().decode([News].self, from: data)
print(self.news)
} catch let error {
print(error)
}
}
}.resume()
}
The fundamental problem is you are retrieving data asynchronously (e.g. getUsers will initiate a relatively slow request from the network using URLSession, but returns immediately). Thus this won’t work:
override func viewDidLoad() {
super.viewDidLoad()
getUsers()
print(news)
}
You are returning from getUsers before the news has been retrieved. So news will still be [].
The solution is to give getUsers a “completion handler”, a parameter where you can specify what code should be performed when the asynchronous request is done:
enum NewsError: Error {
case invalidURL
case invalidResponse(URLResponse?)
}
func getUsers(completion: #escaping (Result<[News], Error>) -> Void) {
let queue = DispatchQueue.main
guard let url = URL(string: "http://prostir.news/swift/api2.php") else {
queue.async { completion(.failure(NewsError.invalidURL)) }
return
}
URLSession.shared.dataTask(with: url) { data, response, error in
if let error = error {
queue.async { completion(.failure(error)) }
return
}
guard
let data = data,
let httpResponse = response as? HTTPURLResponse,
200 ..< 300 ~= httpResponse.statusCode
else {
queue.async { completion(.failure(NewsError.invalidResponse(response))) }
return
}
do {
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .secondsSince1970
let news = try decoder.decode([News].self, from: data)
queue.async { completion(.success(news)) }
} catch let parseError {
queue.async { completion(.failure(parseError)) }
}
}.resume()
}
Then your view controller can fetch the news, passing a “closure”, i.e. code that says what to do when the asynchronous call is complete. In this case, it will set self.news and trigger the necessary UI update (e.g. maybe refresh tableview):
class ViewController: UIViewController {
var news: [News] = []
override func viewDidLoad() {
super.viewDidLoad()
fetchNews()
}
func fetchNews() {
getUsers() { result in
switch result {
case .failure(let error):
print(error)
case .success(let news):
self.news = news
print(news)
}
// trigger whatever UI update you want here, e.g., if using a table view:
//
// self.tableView.reloadData()
}
// but don't try to print the news here, as it hasn't been retrieved yet
// print(news)
}
This question already has an answer here:
Return a string from a web scraping function in swift
(1 answer)
Closed 4 years ago.
How can I return a value within an if let statement to be further returned within a function? Here is the code:
func loadUrl(url:String) -> String {
DispatchQueue.global().async {
do {
let appUrl = URL(string:url)!
let data = try Data(contentsOf:appUrl)
let json = try JSONSerialization.jsonObject(with: data) as! [String:Any]
print("Test from do")
if let results = json["results"] as? [[String:Any]] {
print("Test from if let 1")
if let first = results[0] as? [String:Any] {
print("Test from if let 2")
var cityStateLocation = first["formatted_address"]!
return cityStateLocation
//What needs to be returned
}
}
DispatchQueue.main.async {
print("No Error")
}
} catch {
DispatchQueue.main.async {
print("Cannot connect to the server.")
}
}
}
}
What I would like to be able to do is take cityStateLocation and return it in the func, but because it is a part of an if let statement within an .async method I don't know how to do that. Could someone please explain?
EDIT: I need the return value of cityStateLocation to equal a variable in a separate function. Here is the separate function:
#IBAction func continueButton(_ sender: Any) {
var cityState:String
if locationSwitch.isOn == true {
print(location.latitude)
print(location.longitude)
let url = "https://maps.googleapis.com/maps/api/geocode/json?latlng=\(location.latitude),\(location.longitude)&result_type=locality&key=AIzaSyDI-ZacHyPbLchRhkoaUTDokwj--z_a_jk"
loadUrl(url: url)
cityState = loadUrl(url: url)
} else {
cityState = ""
}
CoreDataHandler.saveObject(locationLocality: cityState)
}
Edit 2: The main reason why the "duplicate answer" is not a duplicate is that my code needs to call the return of this function within a separate function then save it to Core Data. Also, my code is not using an array.
You could modify your function to include a closure. For instance:
func loadUrl(url: String, completionHandler: #escaping (_ location: String?) -> (Void)) {
And then, where you want to return it, you'd pass it in as such.
completionHandler(cityStateLocation)
I made it an optional so that, in your fail paths, you could return nil.
Then, where you call the function would change. Using trailing closure syntax, it could look like this:
loadUrl(url: "someurl.com/filepath.txt") { optionalLocation in
guard let nonOptionalLocation = optionalLocation else {
// Location was nil; Handle error case here
return
}
// Do something with your location here, like setting UI or something
}
This is a fairly common pattern when dealing with asynchronous activity, such as working with network calls.
The simplest (perhaps no the prettiest), way of doing this would simply be to declare and instantiate a variable above the dispatch queue. Then you can set the variable equal to whatever you want, within the dispatch queue, and return it afterwards. You can change the type of ret, so that it suits your needs more directly.
func loadUrl(url:String) -> String {
var ret = NSObject()
DispatchQueue.global().async {
do {
let appUrl = URL(string:url)!
let data = try Data(contentsOf:appUrl)
let json = try JSONSerialization.jsonObject(with: data) as! [String:Any]
print("Test from do")
if let results = json["results"] as? [[String:Any]] {
print("Test from if let 1")
if let first = results[0] as? [String:Any] {
print("Test from if let 2")
var cityStateLocation = first["formatted_address"]!
ret = cityStateLocation
//What needs to be returned
}
}
DispatchQueue.main.async {
print("No Error")
}
} catch {
DispatchQueue.main.async {
print("Cannot connect to the server.")
}
}
}
return ret
}
DispatchQueue.global().async will cause the coded included in the closure to be executed at some point the future, meaning you loadUrl function will return (almost) immediately.
What you need is some kind of callback which can be called when you have a result (AKA closure)
This is just another way to approach the problem, the difference between this and Josh's example is simply, I provide an additional closure to handle the errors
func loadUrl(url:String, complition: #escaping (String?) -> Void, fail: #escaping (Error) -> Void) {
DispatchQueue.global().async {
do {
let appUrl = URL(string:url)!
let data = try Data(contentsOf:appUrl)
let json = try JSONSerialization.jsonObject(with: data) as! [String:Any]
print("Test from do")
if let results = json["results"] as? [[String:Any]], !results.isEmpty {
print("Test from if let 1")
let first = results[0]
print("Test from if let 2")
if let cityStateLocation = first["formatted_address"] as? String {
complition(cityStateLocation)
} else {
complition(nil)
}
} else {
complition(nil)
}
} catch let error {
fail(error)
}
}
}
Which you might call using something like...
loadUrl(url: "your awesome url", complition: { (value) in
guard let value = value else {
// No value
return
}
// process value
}) { (error) in
// Handle error
}
I am using nsurlsession on RxSwift.
I am facing two problems about nsurlsession on RxSwift.
I created Custom Observable.
This Observable has used nsurlsession.
nsurlsession.datataskwithrequst was canceled everytime on RxSwift.
My code is here
func getWorkInfo(request:NSURLRequest,type1:C.Type,type2:W.Type? = nil) -> Observable<(C?,[W]?, NSHTTPURLResponse)>{
return Observable.create { observer in
var d: NSDate?
if Logging.URLRequests(request) {
d = NSDate()
}
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request) { (data, response, error) in
guard let response = response, data = data else {
ColorLogger.defaultInstance?.error(error)
observer.on(.Error(error ?? RxCocoaURLError.Unknown))
return
}
guard let httpResponse = response as? NSHTTPURLResponse else {
observer.on(.Error(RxCocoaURLError.NonHTTPResponse(response: response)))
return
}
guard let jsonString: String = NSString(data:data, encoding:NSUTF8StringEncoding) as? String else{
observer.on(.Error(ApiError.FormatError))
return
}
//カウント系
let countObj = Mapper<C>().map(jsonString)
//一覧系
//二つ目を指定してない場合はnilを返す
if type2 != nil{
let aryObj = Mapper<W>().mapArray(jsonString)
observer.on(.Next(countObj,aryObj, httpResponse))
}else{
observer.on(.Next(countObj,nil, httpResponse))
}
observer.on(.Completed)
}
let t = task
t.resume()
return AnonymousDisposable{task.cancel()}
}
}
Above method was called by here.
func getWorkCount(dicParam: NSDictionary) -> Observable<WorkCount?> {
// URL作成
let strParam = dicParam.urlEncodedString()
let strUrl = Const.ShiftApiBase.SFT_API_DOMAIN+Const.ApiUrl.WORK_COUNT+"?"+strParam
// 求人リストデータを取得
let url = NSURL(string: strUrl)!
let request = NSURLRequest(URL: url)
let client = WorkClient<WorkCount,Work>()
ColorLogger.defaultInstance?.debug(strUrl)
return client.getWorkInfo(request, type1: WorkCount.self)
.observeOn(Dependencies.sharedDependencies.backgroundWorkScheduler)
.catchError{(error) -> Observable<(WorkCount?,[Work]?, NSHTTPURLResponse)> in
print("error")
ColorLogger.defaultInstance?.error("UnknownError")
return Observable.empty()
}
.map { countObj,workObj,httpResponse in
if httpResponse.statusCode != 200 {
throw ApiError.Bad
}
return countObj
}
.observeOn(Dependencies.sharedDependencies.mainScheduler)
}
And My subscribe is here.
/**
検索件数を取得
- parameter param: <#param description#>
*/
func getSearchCount(param: [String:String]){
let dicParam = NSDictionary(dictionary: param)
api.getWorkCount(dicParam)
.catchError{
error -> Observable<WorkCount?> in
switch error{
case ApiError.Bad:
ColorLogger.defaultInstance?.error("status error")
break
case ApiError.FormatError:
ColorLogger.defaultInstance?.error("FormatError")
break
case ApiError.NoResponse:
ColorLogger.defaultInstance?.error("NoResponse")
break
default:
ColorLogger.defaultInstance?.error("UnKnownError")
break
}
return Observable.just(nil)
}
.subscribeNext { [weak self] countObj in
self?.count.value = countObj?.returned_count
}
.addDisposableTo(disposeBag)
}
I have two problems.
1:nsurlsession was canceled every time.I don know reason.
2:Even if I got error on NSURLSession,I could not catch error on "CatchError".
By the way,when i try to use the following code,But nsurlsession might be canceled.
It might be a base nsurlsession on RxSwift.
func getWorkCount4(dicParam: NSDictionary) -> Observable<WorkCount?> {
// URL作成
let strParam = dicParam.urlEncodedString()
let strUrl = Const.ShiftApiBase.SFT_API_DOMAIN+Const.ApiUrl.WORK_COUNT+"?"+strParam
// 求人リストデータを取得
let url = NSURL(string: strUrl)!
let request = NSURLRequest(URL: url)
let session = ApiBase.sharedObj.createNSURLSession()
return NSURLSession.sharedSession().rx_response(request)
.observeOn(Dependencies.sharedDependencies.backgroundWorkScheduler)
.map { data,httpResponse in
if httpResponse.statusCode != Const.HTTP_RESPONSE.HTTP_STATUS_CODE_OK {
throw ApiError.Bad
}
guard let jsonString: String = NSString(data:data, encoding:NSUTF8StringEncoding) as? String else{
throw ApiError.FormatError
}
let countObj = Mapper<WorkCount>().map(jsonString)
return countObj
}
.observeOn(Dependencies.sharedDependencies.mainScheduler)
}
What is this problem?
I could resolve by myself.
Above method does not have any problem.
Below code has problem.
// MARK: - 検索カウント
extension SearchCount{
/// 検索用のViewModel
var searchViewModel:SearchViewModel {
return SearchViewModel()
}
/**
検索の件数を取得
*/
func getSearchCount(){
setApiParameter()
searchViewModel.getSearchCount(apiParam)
}
}
I defined searchViewModel on Class,the i could resolve.
The following functions makes an API call which downloads JSON data and
passes it into an another function imp, which in turn creates the arrays!
func previewer(var spotify_id : [String])
{
var serial_number = 0
for var x in spotify_id
{
let spotify_url = "https://api.spotify.com/v1/tracks/"
let url_with_pars = spotify_url + x
let myurl_1 = NSURL(string: url_with_pars)
let timeout = 15
let request_1 = NSMutableURLRequest(URL: myurl_1!, cachePolicy: .ReloadIgnoringLocalAndRemoteCacheData,
timeoutInterval: 15.0)
let queue = NSOperationQueue()
request_1.HTTPMethod = "GET"
let task = NSURLSession.sharedSession().dataTaskWithRequest(request_1, completionHandler: { (data, response, error) in
//NSURLConnection.sendAsynchronousRequest(request_1, queue: queue, completionHandler: { (reponse, data, error) in
if error != nil
{
print("Error!")
}
else
{
do
{
if let data_1 = try NSJSONSerialization.JSONObjectWithData(data!, options: []) as? NSDictionary
{
self.imp(data_1)
}
else
{
print("error!")
}
}
catch
{
print("error")
}
}
})
//task.resume()
}
print(artist.count)
do_table_refresh()
}
func do_table_refresh()
{
dispatch_async(dispatch_get_main_queue(), {
self.tableView.reloadData()
return
})
}
//FUNCTION WHICH CREATES ARRAY
func imp(var data_1:NSDictionary)
{
if let artist_name = data_1["artists"]![0]["name"] as? String
{
artist.append(artist_name)
}
else
{
print("artist error")
}
if let song_name = data_1["name"] as? String
{
print(song_name)
songs.append(song_name)
}
else
{
print("song error")
}
if let url = data_1["preview_url"] as? String
{
if let url_1 = data_1["id"] as? String
{
url_list.append([url, url_1])
}
else
{
print("url error")
}
}
else
{
var url_2 = data_1["id"] as? String
url_list.append(["null", url_2!])
}
}
Where exactly would you deal with the asynchronous problem any suggestion?
You should note that all the API calls are asynchronous. You are doing a loop of these so, according to your code, you could have several API calls all happening simultaneously.
// Put this outside the loop
let spotify_url = "https://api.spotify.com/v1/tracks/"
for x in spotify_id {
let url_with_pars = spotify_url + x
// Be careful. The following could be nil
let myurl_1 = NSURL(string: url_with_pars)
// Watch out for ! in the following statement.
let request_1 = NSMutableURLRequest(URL: myurl_1!, cachePolicy: .ReloadIgnoringLocalAndRemoteCacheData,
timeoutInterval: 15.0)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request_1, completionHandler: { (data, response, error) in
// handle data here
// refresh table here.
})
task.resume()
}
// When your code gets here, the data may not have come back yet.
// The following WILL NOT WORK
print(artist.count) // Remove me
do_table_refresh() // Remove me
Here's the problem with this approach. The table will be refreshed each time one of the API calls comes back. If you had 10 API calls, that would be 10 refreshes.
Is there a reason you use NSDictionary? Parsing JSON returns [AnyObject] which you can cast as needed.