I have created a custom DataManager class. Inside it I want to fetch data in a method and return an NSData object to convert to JSON afterwards.
I have tried to get the data using the completionHandler but no luck:
class func fetchData() -> NSData? {
var session = NSURLSession.sharedSession(),
result = NSData?()
let DataURL : NSURL = NSURL(string: "http://...file.json")!
let sessionTask = session.dataTaskWithURL(DataURL, completionHandler: { (data: NSData!, response: NSURLResponse!, error: NSError!) -> Void in
result = data
})
sessionTask.resume()
return result
}
The dataTask runs asynchronously. That means that the completion handler closure will not be called by the time you return from fetchData. Thus, result will not have been set yet.
Because of this, you should not try to retrieve data synchronously from an asynchronous method. Instead, you should employ an asynchronous completion handler pattern yourself:
class func fetchData(completion: #escaping (Data?, Error?) -> Void) {
let session = URLSession.shared
let url = URL(string: "http://...file.json")!
let task = session.dataTask(with: url) { data, response, error in
completion(data, error)
}
task.resume()
}
And you'd call it like so:
MyClass.fetchData { data, error in
guard let data = data, error == nil else {
print(error ?? "Unknown error")
return
}
// use `data` here; remember to dispatch UI and model updates to the main queue
}
// but do not try to use `data` here
...
FYI, for the original pre-Swift 3 syntax, see previous revision of this answer.
Related
I am writing a library, So not using UIKit, Even in my iOS app same code works, but when i execute in command line in doesn't . In PlayGround also it seems working.
For some reason callback is not getting triggered, so print statements are not executing.
internal class func post(request: URLRequest, responseCallback: #escaping (Bool, AnyObject?) -> ()) {
execTask(request: request, taskCallback: { (status, resp) -> Void in
responseCallback(status, resp)
})
}
internal class func clientURLRequest(url: URL, path: String, method: RequestMethod.RawValue, params: Dictionary<String, Any>? = nil) -> URLRequest {
var request = URLRequest(url: url)
request.httpMethod = method
do {
let jsonData = try JSONSerialization.data(withJSONObject: (params! as [String : Any]), options: .prettyPrinted)
request.setValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
request.httpBody = jsonData
} catch let error as NSError {
print(error)
}
return request
}
private class func execTask(request: URLRequest, taskCallback: #escaping (Bool,
AnyObject?) -> ()) {
let session = URLSession(configuration: URLSessionConfiguration.default)
print("THIS LINE IS PRINTED")
let task = session.dataTask(with: request, completionHandler: {(data, response, error) -> Void in
if let data = data {
print("THIS ONE IS NOT PRINTED")
let json = try? JSONSerialization.jsonObject(with: data, options: [])
if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
taskCallback(true, json as AnyObject?)
} else {
taskCallback(false, json as AnyObject?)
}
}
})
task.resume()
}
Edits -: I am writing a library, So not using UIKit, Even in my iOS app same code works, but when i execute in command line in doesn't . In PlayGround also it seems working.
I made a simple App from scratch. (Xcode 8 beta 6 / swift 3)
In controller I pasted Your code. (plus url creation..)
I see all in debugger:
THIS ONE IS PRINTED
THIS ONE IS PRINTED, TOO
I AM BACK
so it seems workin.
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let URLString = "https://apple.com"
let url = URL(string: URLString)
let request = URLRequest(url: url!)
ViewController.execTask(request: request) { (ok, obj) in
print("I AM BACK")
}
}
private class func execTask(request: URLRequest, taskCallback: #escaping (Bool,
AnyObject?) -> ()) {
let session = URLSession(configuration: URLSessionConfiguration.default)
print("THIS LINE IS PRINTED")
let task = session.dataTask(with: request, completionHandler: {(data, response, error) -> Void in
if let data = data {
print("THIS ONE IS PRINTED, TOO")
let json = try? JSONSerialization.jsonObject(with: data, options: [])
if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
taskCallback(true, json as AnyObject?)
} else {
taskCallback(false, json as AnyObject?)
}
}
})
task.resume()
}
}
I know its late for the answer but in case you have not figure out the issue or getting issue at other places, lets try this.
You need to save session variable outside method scope (make it a instance variable). Since you defined it locally in function scope. Its get deallocated before completion handler can be called, remember completion handler can't retain your session object and after execution of run loop, garbage collector will dealloc your session object. We need to retain such objects whenever we want call back from delegates or from completion handler..
self.session = URLSession(configuration: URLSessionConfiguration.default)
Did the changes suggested here, It works now.
Using NSURLSession from a Swift command line program
var sema = DispatchSemaphore( value: 0 )
private func execTask(request: URLRequest, taskCallback: #escaping (Bool,
AnyObject?) -> ()) {
let session = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: nil )
session.dataTask(with: request) {(data, response, error) -> Void in
if let data = data {
let json = try? JSONSerialization.jsonObject(with: data, options: [])
if let response = response as? HTTPURLResponse , 200...299 ~= response.statusCode {
taskCallback(true, json as AnyObject?)
} else {
taskCallback(false, json as AnyObject?)
}
}
}.resume()
sema.wait()
}
let dataTask = session.dataTask(with: request, completionHandler: {data, response,error -> Void in
print("Request : \(response)")
let res = response as! HTTPURLResponse
print("Status Code : \(res.statusCode)")
let strResponse = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)
print("Response String :\(strResponse)")
})
dataTask.resume()
Swift 3.0
Just copy below code into your view controller.
#IBAction func btnNewApplicationPressed (_ sender: UIButton) {
callWebService()
}
func callWebService() {
// Show MBProgressHUD Here
var config :URLSessionConfiguration!
var urlSession :URLSession!
config = URLSessionConfiguration.default
urlSession = URLSession(configuration: config)
// MARK:- HeaderField
let HTTPHeaderField_ContentType = "Content-Type"
// MARK:- ContentType
let ContentType_ApplicationJson = "application/json"
//MARK: HTTPMethod
let HTTPMethod_Get = "GET"
let callURL = URL.init(string: "https://itunes.apple.com/in/rss/newapplications/limit=10/json")
var request = URLRequest.init(url: callURL!)
request.timeoutInterval = 60.0 // TimeoutInterval in Second
request.cachePolicy = URLRequest.CachePolicy.reloadIgnoringLocalCacheData
request.addValue(ContentType_ApplicationJson, forHTTPHeaderField: HTTPHeaderField_ContentType)
request.httpMethod = HTTPMethod_Get
let dataTask = urlSession.dataTask(with: request) { (data,response,error) in
if error != nil{
return
}
do {
let resultJson = try JSONSerialization.jsonObject(with: data!, options: []) as? [String:AnyObject]
print("Result",resultJson!)
} catch {
print("Error -> \(error)")
}
}
dataTask.resume()
}
Sometimes, for me, the solution when completionHandler were not called in these cases was because the flag "Allow Arbitrary loads" on Info.plist was defined as NO.
Allow Arbitrary loads flag defined as YES
I am currently trying to download, parse and print JSON from an URL.
So far I got to this point:
1) A class (JSONImport.swift), which handles my import:
var data = NSMutableData();
let url = NSURL(string:"http://headers.jsontest.com");
var session = NSURLSession.sharedSession();
var jsonError:NSError?;
var response : NSURLResponse?;
func startConnection(){
let task:NSURLSessionDataTask = session.dataTaskWithURL(url!, completionHandler:apiHandler)
task.resume();
self.apiHandler(data,response: response,error: jsonError);
}
func apiHandler(data:NSData?, response:NSURLResponse?, error:NSError?)
{
do{
let jsonData : NSDictionary = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as! NSDictionary;
print(jsonData);
}
catch{
print("API error: \(error)");
}
}
My problem is, that the data in
do{
let jsonData : NSDictionary = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as! NSDictionary;
print(jsonData);
}
remains empty.
When I debug,the connection starts successfully, with the given url as a parameter. But my jsonData variable doesn't get printed. Instead the catch block throws the error, stating that there is no data in my variable:
API error: Error Domain=NSCocoaErrorDomain Code=3840 "No value."
Can someone please help me with this?
What am I missing?
Thank you all very much in advance!
[Edited after switching from NSURL Connection to NSURLSession]
Here's an example on how to use NSURLSession with a very convenient "completion handler".
This function contains the network call and has the "completion handler" (a callback for when the data will be available):
func getDataFrom(urlString: String, completion: (data: NSData)->()) {
if let url = NSURL(string: urlString) {
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(url) { (data, response, error) in
// print(response)
if let data = data {
completion(data: data)
} else {
print(error?.localizedDescription)
}
}
task.resume()
} else {
// URL is invalid
}
}
You can use it like this, inside a new function, with a "trailing closure":
func apiManager() {
getDataFrom("http://headers.jsontest.com") { (data) in
do {
let json = try NSJSONSerialization.JSONObjectWithData(data, options: [])
if let jsonDict = json as? NSDictionary {
print(jsonDict)
} else {
// JSON data wasn't a dictionary
}
}
catch let error as NSError {
print("API error: \(error.debugDescription)")
}
}
}
I am getting this error This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.This will cause an exception in a future release. I don't know what is causing this error. Can anybody help me.
func getUserDataFromTwitterWithUser(user : PFUser)
{
//NRLoader.showLoader()
let strTwURL = "https://api.twitter.com/1.1/users/show.json? screen_name="+PFTwitterUtils.twitter()!.screenName! + "&access_token="+PFTwitterUtils.twitter()!.authToken!
let twURL = NSURL (string: strTwURL)
let request = NSMutableURLRequest(URL: twURL!, cachePolicy: NSURLRequestCachePolicy.UseProtocolCachePolicy, timeoutInterval: 2.0) as NSMutableURLRequest
PFTwitterUtils.twitter()?.signRequest(request)
let session = NSURLSession.sharedSession()
session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
if error == nil {
var jsonOptional = Dictionary<String, AnyObject>()
do {
jsonOptional = try NSJSONSerialization.JSONObjectWithData(data!, options:NSJSONReadingOptions.MutableContainers ) as! Dictionary<String, AnyObject>
// use jsonData
} catch {
// report error
}
var userName = ""
if let screenName = jsonOptional["screen_name"] as? String{
userName = screenName
}
else if let name = jsonOptional["name"] as? String{
userName = name
}
var profilePicUrl = ""
if let picUrl = jsonOptional["profile_image_url"] as? String{
profilePicUrl = picUrl
}
AppUser.currentUser()?.username = userName
AppUser.currentUser()?.profileAwsURL = profilePicUrl
//NRLoader.hideLoader()
//if ParseUtils.isLoggedInUserIsAnonymous() {
let signUpVC:SignMeUpViewController = self.storyboard!.instantiateViewControllerWithIdentifier("SignMeUpViewController") as! SignMeUpViewController
signUpVC.isFromLogin = true
self.navigationController!.pushViewController(signUpVC, animated: true)
//} else {
// self.pushToSubmitDreamViewController()
//}
}
else {
//NRLoader.hideLoader()
NRToast.showToastWithMessage(error!.description)
}
}).resume()
}
The dataTaskWithRequest call runs in the background and then calls your completion handler from the same thread. Anything that updates the UI should run on the main thread, so all of your current handler code should be within a dispatch_async back onto the main queue:
dispatch_async(dispatch_get_main_queue()) {
// Do stuff to UI
}
Swift 3:
DispatchQueue.main.async() {
// Do stuff to UI
}
Therefore, ideally all the code you currently have within if error == nil should be off in another function, say called handleRequest, so your current code becomes:
session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
if error == nil {
dispatch_async(dispatch_get_main_queue(), {
self.handleRequest(...)I
})
}
Swift 3
session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
if error == nil {
DispatchQueue.main.async {
self.handleRequest(...)I
}
}
Should try Symbolic Breakpoint to detect the issue:-
Then put your UI Update code in main thread
DispatchQueue.main.async {}
You'd better change UI only in the main thread
swift3,
let liveInfoUrl = URL(string: "http://192.168.1.66/api/cloud/app/liveInfo/7777")
let task = URLSession.shared.dataTask(with: liveInfoUrl! as URL) {data, response, error in
guard let data = data, error == nil else { return }
DispatchQueue.main.async {
print(String(data: data, encoding: String.Encoding(rawValue: String.Encoding.utf8.rawValue)) ?? "aaaa")
//do some ui work
}
}
if the above suggestions still give you no joy then the sure-est way is to redesign your functions so that getting what you need with
URLSession.shared.dataTask
then hands over so a variable declared outside that function, then a separate UIControl ( button, swipe etc ) displays it to a label or textview or whatever.
After all that is what the error message is telling you. they're separate concerns
I am currently trying to nest Alamofire requests to use data that I have already successfully received using GET requests.
For this piece of code I have used Rob's answer in this question
How to return value from Alamofire
However, I can not either nest the Alamofire requests or use them by separate.
This is what I am trying to do
override func viewDidLoad() {
super.viewDidLoad()
var currentFoodType: String = ""
var currentFoodList: String = ""
//debug
//this is how I get back the token from NSUserDefault
if let myToken = userDefaults.valueForKey("token"){
// calling method to get the user info
getUserInfo(myToken as! String)
// calling method to get the product type
func getFoodCategory(completionHandler: (NSDictionary?, NSError?) -> ()) {
getProductTypes(myToken as! String, completionHandler: completionHandler)
}
getFoodCategory() { responseObject, error in
// use responseObject and error here
let foodTypesJSON = JSON(responseObject!)
//to get one single food category
currentFoodType = (foodTypesJSON["types"][0].stringValue)
print(currentFoodType)
/////////////////////////////////////////
func getFoodsByCategory(completionHandler: (NSDictionary?, NSError?) -> ()) {
print("getting " + currentFoodType)
self.getProductsByType(myToken as! String, productType: currentFoodType, completionHandler: completionHandler)
}
getFoodsByCategory() { responseObject, error in
// use responseObject and error here
print("responseObject = \(responseObject); error = \(error)")
return
}
return
}
}
Then the two other functions I am calling from there are very straight forward Alamofire requests with callbacks to the completionHandlers above
//GET THE PRODUCT TYPES FROM THE SERVER
func getProductTypes(myToken: String, completionHandler: (NSDictionary?, NSError?) -> ()) {
let requestToken = "Bearer " + myToken
let headers = ["Authorization": requestToken]
let getProductTypesEndpoint: String = BASE_URL + PRODUCT_TYPES
Alamofire.request(.GET, getProductTypesEndpoint, headers: headers)
.responseJSON{ response in
switch response.result {
case .Success(let value):
completionHandler(value as? NSDictionary, nil)
case .Failure(let error):
completionHandler(nil, error)
}
}//END ALAMOFIRE GET responseJSON
}
The above function returns a single food like "Desserts" which will be used in the following function to GET all the desserts from the server
//GET THE PRODUCTS FROM THE SERVER GIVEN A CATEGORY
func getProductsByType(myToken: String, productType: String, completionHandler: (NSDictionary?, NSError?) -> ()){
let requestToken = "Bearer " + myToken
let headers = ["Authorization": requestToken]
let getProductTypesEndpoint: String = BASE_URL + PRODUCT_BY_TYPE + productType
Alamofire.request(.GET, getProductTypesEndpoint, headers: headers)
.responseJSON { response in
switch response.result {
case .Success(let value):
print("no errors")
let auth = JSON(value)
print("The pbt GET description is: " + auth.description)
completionHandler(value as? NSDictionary, nil)
case .Failure(let error):
print("there was an error")
completionHandler(nil, error)
}
}//END ALAMOFIRE GET responseJSON
}
and this works well because when I print within the getProductsByType function
using
print("The pbt GET description is: " + auth.description)
I get the JSON with all the products but the problem is in the viewDidload function where I am nesting the callbacks
getFoodsByCategory() { responseObject, error in
// use responseObject and error here
print("responseObject = \(responseObject); error = \(error)")
return
}
the print within that bit is showing me that something is wrong so I can not parse my response as I desire.
Because I get the following
responseObject = nil; error = nil
So my guess is that there must a be a different method to nest these callbacks?
Take a look at chained promises from PromiseKit. This also works well with Alamofire:
func loadFoo() -> Promise<Bar> {
return Promise<Bar> { fulfill, reject in
Alamofire.request(.GET, "url")
.responseJSON { response in
switch response.result {
case .Success(let value):
let bar = Bar(fromJSON: value)
fulfill(bar)
case .Failure(let error):
reject(error)
}
}
}
}
// Usage
getBar()
.then { bar -> Void in
// do something with bar
}
.error { error in
// show error
}
This is very simple example, but you can find more relevant examples in documentation.
Im having an issue, I am trying to create a method which accepts a PFObject as a parameter. The PFObject in this case is the facebook picture URL. The method takes the URL and basically converts it into an image. I can get it to work if i just use this block of code without trying to make it into a method, however I would like to create a method out of this so that I dont have to keep repeating myself. When i try to return the users image i keep getting the error cannot convert the expressions type UIImage to type void swift
Here is the code
func downloadFBUserImage(object: PFObject?) -> UIImage? {
var userProfilePhotoURLString = object?.valueForKey("pictureURL") as String?
if userProfilePhotoURLString != nil {
var pictureURL: NSURL = NSURL(string: userProfilePhotoURLString!)!
var urlRequest: NSURLRequest = NSURLRequest(URL: pictureURL)
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue(), completionHandler: { (NSURLResponse response, NSData data, NSError error) -> Void in
if error == nil && data != nil {
var userProfilePic: UIImage? = UIImage(data: data)
return userProfilePic
}
})
return nil
}
The error is reporting that the completionHandler of the sendAsynchronousRequest is defined to pass you the response, data, and error objects, but that it expects that completionHandler, itself, to not return any values. But you're trying to return a value from within that completionHandler closure.
Bottom line, you cannot simply return the UIImage from your function, because you are performing asynchronous method (i.e. the data is returned later even though you return from the function immediately). So, employ asynchronous pattern:
func downloadFBUserImage(object: PFObject?, completionHandler: (UIImage?, NSError?) -> Void) {
if let userProfilePhotoURLString = object?.valueForKey("pictureURL") as? String {
let pictureURL = NSURL(string: userProfilePhotoURLString)!
let urlRequest = NSURLRequest(URL: pictureURL)
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue()) { (response, data, error) -> Void in
if data != nil {
var userProfilePic = UIImage(data: data)
completionHandler(userProfilePic, nil)
} else {
completionHandler(nil, error)
}
}
}
}
And you'd call it using the same completion handler pattern that sendAsynchronousRequest does:
downloadFBUserImage(object) { image, error in
if image == nil {
println(error)
} else {
// use the image here
}
}
// but don't try to use asynchronously retrieved image here
You cannot return to the completion block like that. The completion block does not have a return parameter. This is why you are getting an error.
For updating the image after download, you can pass in a block along with your downloadFBUserImage function like below.
I used dispatch_async because UI updates have to be done on the main thread.
func downloadFBUserImage(object: PFObject?, completion completionBlock:(UIImage) -> ()) -> (){
var userProfilePhotoURLString = object?.valueForKey("pictureURL") as String?
if userProfilePhotoURLString != nil {
var pictureURL: NSURL = NSURL(string: userProfilePhotoURLString!)!
var urlRequest: NSURLRequest = NSURLRequest(URL: pictureURL)
NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue(), completionHandler: { (NSURLResponse response, NSData data, NSError error) -> Void in
if error == nil && data != nil {
if let userProfilePic = UIImage(data: data) {
completionBlock(userProfilePic)
}
}
})
}
}
It can be called like this
func do() {
downloadFBUserImage(pfObject, completion: { (image) -> () in
//updateImage
dispatch_async(dispatch_get_main_queue(), { () -> Void in
// UI updates
}
})
}