This is my code, by which I am trying to catch the error, when server is down:
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
if error != nil
{
self.displayMessage(userMessage: "Could not successfully perform this request. Please check yourr internet connection.")
print("error=\(String(describing: error))")
return
}
do {
let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
if let parseJSON = json {
if parseJSON["errorMessageKey"] != nil
{
self.displayMessage(userMessage: parseJSON["errorMessage"] as! String)
return
}
...
} else {
self.displayMessage(userMessage: "Could not successfully perform this request. Please try again later")
}
} catch {
self.displayMessage(userMessage: "Could not successfully perform this request. Please try again later")
print(error)
}
}
task.resume()
But in console I get "XPC connection error", instead of displaying alert.
How can I display Alert, when this error occures?
My environment:
Swift: 5
Xcode: 11.5
Target deployment: 13.4
Assuming displayMessage has no problem as you have not provided the code.
I would suggest you call the code which has the UIKit API, on the main thread. As the dataTask completion block is always called on a background thread. I would suggest you while calling the function which further has the code related to UIKit should always run on the main thread
Use UIKit classes only from your app’s main thread or main dispatch
queue, unless otherwise indicated. This restriction particularly
applies to classes derived from UIResponder or that involve
manipulating your app’s user interface in any way.
Have a look at the updated code snippet.
let task = URLSession.shared.dataTask(with: request) { (data: Data?, response: URLResponse?, error: Error?) in
// It ensure rest code placed inside run on the main thread. I assume displayMessage function having the code related to UIKit framework.
DispatchQueue.main.async {
if error != nil
{
self.displayMessage(userMessage: "Could not successfully perform this request. Please check yourr internet connection.")
print("error=\(String(describing: error))")
return
}
do {
let json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSDictionary
if let parseJSON = json {
if parseJSON["errorMessageKey"] != nil
{
self.displayMessage(userMessage: parseJSON["errorMessage"] as! String)
return
}
} else {
self.displayMessage(userMessage: "Could not successfully perform this request. Please try again later")
}
} catch {
self.displayMessage(userMessage: "Could not successfully perform this request. Please try again later")
print(error)
}
}
}
task.resume()
Related
I am trying to do some parsing of HTML on client side using Swift inside Xcode Project. I first tested this function inside playgrounds for a variety of URLs, and it downloads instantly for all my use cases. However, running this inside my Xcode project for iOS (even when disabling ATS in my info.plist), the URLSession will not download anything for many of the URLs to common websites that worked in playgrounds. It will still download some, such as the html of apple.com. Can anybody explain what I might be missing or need to enable/disable to get this to work.
func fetchHTMLString(url: URL) {
let task = URLSession.shared.downloadTask(with: url) { localURL, urlResponse, error in
if let localURL = localURL {
if let string = try? String(contentsOf: localURL) {
print("String here")
self.sortData(htmlString: string)
} else {
print("couldnt get as string")
}
}
}
task.resume()
print("going")
}
Update, I attempted to change this function to use URLSession data task, and was able to successfully download. I am, however, now just curious to find out why this would allow the download to complete with data task and not with download task. Here's the code that works
func fetchHTMLString(url: URL) {
let task = URLSession.shared.dataTask(with: url) { data, response, error in
if let error = error {
print("Error \(error.localizedDescription)")
} else if let data = data, let response = response as? HTTPURLResponse {
if response.statusCode == 200 {
if let string = String(data: data, encoding: .utf8) {
print(string)
self.sortData(htmlString: string)
print("String here")
} else {
print("couldn't get as string")
}
} else {
print("Error \(response.statusCode)")
}
} else {
print("No data or error returned.")
}
}
task.resume()
print("going")
}
```
I am obviously missing something very fundamental/naïve/etc., but for the life of me I cannot figure out how to make simple GET requests.
I'm trying to make an HTTP GET request with Swift 5. I've looked at these posts/articles: one, two, but I can't get print() statements to show anything. When I use breakpoints to debug, the entire section within the URLSession.shared.dataTask section is skipped.
I am looking at the following code (from the first link, above):
func HTTP_Request() {
let url = URL(string: "http://www.stackoverflow.com")!
let task = URLSession.shared.dataTask(with: url) {(data: Data?, response: URLResponse?, error: Error?) in
guard let data = data else { return }
print(String(data: data, encoding: .utf8)!)
}
task.resume()
}
HTTP_Request()
I am running this in a MacOS Command Line Project created through XCode.
I would greatly appreciate any help I can get on this, thank you.
Right now, if there is an error, you are going to silently fail. So add some error logging, e.g.,
func httpRequest() {
let url = URL(string: "https://www.stackoverflow.com")! // note, https, not http
let task = URLSession.shared.dataTask(with: url) { data, response, error in
guard
error == nil,
let data = data,
let string = String(data: data, encoding: .utf8)
else {
print(error ?? "Unknown error")
return
}
print(string)
}
task.resume()
}
That should at least give you some indication of the problem.
A few other considerations:
If command line app, you have to recognize that the app may quit before this asynchronous network request finishes. One would generally start up a RunLoop, looping with run(mode:before:) until the network request finishes, as advised in the run documentation.
For example, you might give that routine a completion handler that will be called on the main thread when it is done. Then you can use that:
func httpRequest(completion: #escaping () -> Void) {
let url = URL(string: "https://www.stackoverflow.com")! // note, https, not http
let task = URLSession.shared.dataTask(with: url) { data, response, error in
defer {
DispatchQueue.main.async {
completion()
}
}
guard
error == nil,
let data = data,
let string = String(data: data, encoding: .utf8)
else {
print(error ?? "Unknown error")
return
}
print(string)
}
task.resume()
}
var finished = false
httpRequest {
finished = true
}
while !finished {
RunLoop.current.run(mode: .default, before: .distantFuture)
}
In standard macOS apps, you have to enable outgoing (client) connections in the “App Sandbox” capabilities.
If playground, you have to set needsIndefiniteExecution.
By default, macOS and iOS apps disable http requests unless you enable "Allow Arbitrary Loads” in your Info.plist. That is not applicable to command line apps, but you should be aware of that should you try to do this in standard macOS/iOS apps.
In this case, you should just use https and avoid that consideration altogether.
Make sure the response get print before exiting the process, you could try to append
RunLoop.main.run()
or
sleep(UINT32_MAX)
in the end to make sure the main thread won't exit. If you want to print the response and exit the process immediately, suggest using DispatchSemaphore:
let semphare = DispatchSemaphore(value: 0)
func HTTP_Request() {
let url = URL(string: "http://www.stackoverflow.com")!
let task = URLSession.shared.dataTask(with: url) {(data: Data?, response: URLResponse?, error: Error?) in
guard let data = data else { return }
print(String(data: data, encoding: .utf8)!)
semphare.signal()
}
task.resume()
}
HTTP_Request()
_ = semphare.wait(timeout: .distantFuture)
This works for me many times I suggest you snippet for future uses!
let url = URL(string: "https://google.com")
let task = URLSession.shared.dataTask(with: ((url ?? URL(string: "https://google.com"))!)) { [self] (data, response, error) in
do {
let jsonResponse = try JSONSerialization.jsonObject(with: data!, options: [])
print(jsonResponse)
guard let newValue = jsonResponse as? [String:Any] else {
print("invalid format")
}
}
catch let error {
print("Error: \(error)")
}
task.resume()
}
I am using a do catch scenario to try a JSONDecoder(), the only >problem is that I keep catching the error, but when I review my code I >can't see the error, maybe I need another set of eyes to help me out >of this one!
I placed my JSON file in a storage folder in turbo360, I've also tried gitHub, but neither is working, I believe.
import UIKit
class ViewController: UIViewController {
final let url = URL(string: "https://storage.turbo360.co/portfolio-website-hxoc6m/actors")
override func viewDidLoad() {
super.viewDidLoad()
downloadJson()
}
func downloadJson() {
guard let downloadURL = url else { return }
URLSession.shared.dataTask(with: downloadURL) { data, urlResponse, error in
guard let data = data, error == nil, urlResponse != nil else {
print("something is wrong")
return
}
print("downloaded")
print(downloadURL)
do
{
let decoder = JSONDecoder()
let actors = try decoder.decode(Actors.self, from: data)
print(actors)
} catch {
print("Something wrong after downloaded")
}
}.resume()
}
}
I supposed to get: JSONDonloadingSwift4.Actors
as confirmation that my JSON file has been accessed and decoded
Your JSON is invalid. You are missing an opening " on the last image URL. Fix that and as long as your Actor definition matches you should be good. jsonlint is very useful for checking JSON structure.
thanks for any help upfront.
url session works perfect with connection, it prints the error as nil. but without it it prints the .localizedDescription just fine and shows me the right error, but then continues to do the do{ try } and crashes with this error in the try line:
Thread 6: Fatal error: Unexpectedly found nil while unwrapping an
Optional value
now I am not even sure if this has anything to do with the errorhandling. thanks for any help with understanding whats going on or just solving the problem!
func getData(completion: (() -> ())?) {
let urlString = URL(string: "https://api.coinmarketcap.com/v1/ticker/")
URLSession.shared.dataTask(with: urlString!, completionHandler: { (data, response , error) in
print("before entering do-try-catch", error?.localizedDescription)
do {
//create Dictionary
print("downloading content")
self.coinData = try JSONSerialization.jsonObject(with: data!) as! [[String:Any]]
//set connection status
self.connection = true
//update tableView
DispatchQueue.main.async {
completion?()
}
} catch {
print("catch", error.localizedDescription)
//set connection status
self.connection = false
//update tableView
DispatchQueue.main.async {
completion?()
}
}
}).resume()
}
Thread 6: Fatal error: Unexpectedly found nil while unwrapping an Optional value is a common problem for beginners.
You try to work with data that is not there.
So for example in your code you force to execute try JSONSerialization.jsonObject(with: data!)
When data is nil the code will crash.
The same at the beginning URLSession.shared.dataTask(with: urlString!, completionHandler: { (data, response, error) {}
When urlString is not a valid URL the code will be crash. (In this case the url seems to be valid).
For more information have a look here:
https://stackoverflow.com/a/24034551/4420355
Try the following snipped it should work
if let data = data {
self.coinData = try JSONSerialization.jsonObject(with: data) as? [[String:Any]]
//... work with coinData
}
Reason why it is crashing is because data is Optional and it should be nil or has some value. On line
self.coinData = try JSONSerialization.jsonObject(with: data!) as! [[String:Any]]
Compiler thinks:
Let's take a look and unwrap this Optianal variable. But it's nil, there is "nothing"! So what should I unwrap? Let's crash and throw Fatal Error message.
How to easily avoid this with Optional binding:
if let data = data {
....do something with data
} else {
...print error message
}
For more information take look at this brilliant answer.
https://stackoverflow.com/a/32170457/3046686
I am trying to use swiftyjson and I am getting an Error:
Call can throw, but it is marked with 'try' and the error is not
handled.
I have validated that my source JSON is good. I've been searching and cannot find a solution to this problem
import Foundation
class lenderDetails
{
func loadLender()
{
let lenders = ""
let url = URL(string: lenders)!
let session = URLSession.shared.dataTask(with: url)
{
(data, response, error) in
guard let data = data else
{
print ("data was nil?")
return
}
let json = JSON(data: data)
print(json)
}
session.resume()
}
}
Thank you for all the help!
The SwiftyJSON initializer throws, the declaration is
public init(data: Data, options opt: JSONSerialization.ReadingOptions = []) throws
You have three options:
Use a do - catch block and handle the error (the recommended one).
do {
let json = try JSON(data: data)
print(json)
} catch {
print(error)
// or display a dialog
}
Ignore the error and optional bind the result (useful if the error does not matter).
if let json = try? JSON(data: data) {
print(json)
}
Force unwrap the result
let json = try! JSON(data: data)
print(json)
Use this option only if it's guaranteed that the attempt will never fail (not in this case!). Try! can be used for example in FileManager if a directory is one of the default directories the framework creates anyway.
For more information please read Swift Language Guide - Error Handling
You should wrap it into a do-catch block. In your case:
do {
let session = URLSession.shared.dataTask(with: url) {
(data, response, error) in
guard let data = data else {
print ("data was nil?")
return
}
let json = JSON(data: data)
print(json)
}
} catch let error as NSError {
// error
}
Probably you need to implement do{} catch{} block. Inside do block you have to call throwable function with try.