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.
Related
I was trying to make my code clean and decouple the code below, I want to remove the trailing completion handler from it and write the completion handler in another blck of code.
func uploadMarcasMetodoNovo(_ id_resenha: Int) {
let resenhaDados:ResDadoModel = db.readDadosResenhaById(id_resenha)
let resenhaMarcas:[ResMarcasModel] = db.readResMarca(id_resenha)
// this for loop runs about for 7 times
for marca in resenhaMarcas {
contadorUploadMarcas = contadorUploadMarcas + 1
myUploadGroupMarcas.enter()
jsonRequestUploadImagemGrafica = ResMarcasModel.createJsonMarcaResenha(marca, resenhaDados.IdGedave )
let json: [String: Any] = jsonRequestUploadImagemGrafica
guard let jsonData = try? JSONSerialization.data(withJSONObject: json) else {
print("guard jsonData error")
return
}
let requestImagemGrafica = requestUploadFotos(jsonData)
let task = URLSession.shared.dataTask(with: requestImagemGrafica) { data, response, error in
if let error = error {
print("error: \(String(describing: error))")
return
}
print("data")
guard let returnData = String(data: data!, encoding: .utf8) else {
print("returnData guard fail")
return
}
print("returnData")
print(returnData)
self.confirmStatusEnviada(marca)
self.myUploadGroupMarcas.leave()
print("end TASK")
}
task.resume()
}
myUploadGroupMarcas.notify(queue: DispatchQueue.main) {
print("myUploadGroupMarcas notify")
// more code ...
}
}
This is the part that I write creating a separated completion handler
let myCompletionHandler: (Data?, URLResponse?, Error?) -> Void = {
(data, response, error) in
if let error = error {
print("error: \(String(describing: error))")
return
}
print("data")
guard let returnData = String(data: data!, encoding: .utf8) else {
print("returnData guard fail")
return
}
self.confirmStatusEnviada(marca)
self.myUploadGroupMarcas.leave()
}
but it won't work because in the last two lines of code are used paramters that are out of scope. The parameter "marca" and the parameter "myUploadGroupMarcas" are out of scope. Is there a way to use these parameters inside the separated completion handler function?
Ok based on our comments above, this is the route I would try: Write a short completion handler that calls your longer completion handler, passing the variables that are out of scope.
let task = URLSession.shared.dataTask(with: requestImagemGrafica) { data, response, error in
myCompletionHandler(data, response, error, marca, myUploadGroupMarcas)
}
Then you add two parameters to your completion handler in the function definition:
let myCompletionHandler: (Data?, URLResponse?, Error?, MarcaClass, myUploadGroupMarcas) -> Void
Obviously you need to replace MarcaClass with the actual class type that is marca and myUploadGroupMarcas seems to be a function so you'd need to write an appropriate parameter type for that.
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've created a macOS console app in swift, but the code is never executed, =I have to use Semaphore but is there another way to do this ?
my purpose is to create a method returning a json file
class test{
func gizlo(){
let config = URLSessionConfiguration.default // Session Configuration
let session = URLSession(configuration: config) // Load configuration into Session
let url = URL(string: "https://itunes.apple.com/fr/rss/topmovies/limit=25/json")!
let task = session.dataTask(with: url, completionHandler: {
(data, response, error) in
if error != nil {
print(error!.localizedDescription)
} else {
do {
if let json = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
{
print(json)
}
} catch {
print("error in JSONSerialization")
}
}
})
task.resume()
}
}
let tr=test()
tr.gizlo()
Thanks
To avoid Semaphores you can use simple readLine() that will wait for input from the keyboard. Yes it is not obvious but it is woking because it prevent terminal app from exit.
Just add in the and of the file:
_ = readLine()
As Oleg points out, putting readLine() at the end of the top-level code will prevent the program for exiting until you hit Enter in the terminal or wherever FileHandle.standardInput is pointing. That's probably fine for just testing the code quickly in the debugger or in a Playground. An infinite loop would also work, though you'd have to actually terminate it in the debugger or with kill from the command line.
The real issue is why you don't want to use a semaphore. Since they're not difficult to use, I'm going to hazard a guess that it's just because you don't want to pollute your asynchronous data task completion handler with a semaphore when you probably only need it to wait for the data for testing purposes.
Assuming my guess is correct, the real issue isn't actually using a semaphore, it's where you think you need to put them. As David Wheeler once said, "Any problem can be solved by adding a layer of indirection."
You don't want the semaphore explicitly in the completion handler you pass to dataTask. So one solution would be to make gizlo accept a completion handler of its own, and then create a method that calls gizlo with a closure that handles the semaphore. That way you can decouple the two and even add some flexibility for other uses. I've modified your code to do that:
import Foundation
import Dispatch // <-- Added - using DispatchSemaphore
class test{
func gizlo(_ completion: ((Result<[String: Any]?, Error>) -> Void)? = nil) { // <-- Added externally provided completion handler
let config = URLSessionConfiguration.default // Session Configuration
let session = URLSession(configuration: config) // Load configuration into Session
let url = URL(string: "https://itunes.apple.com/fr/rss/topmovies/limit=25/json")!
let task = session.dataTask(with: url, completionHandler: {
(data, response, error) in
let result: Result<[String: Any]?, Error>
if let responseError = error { // <-- Changed to optional binding
print(responseError.localizedDescription)
result = .failure(responseError) // <-- Added this
} else {
do {
if let json = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
{
print(json)
result = .success(json) // <-- Added this
}
else { // <-- Added this else block
result = .success(nil)
}
} catch {
print("error in JSONSerialization")
result = .failure(error) // <-- Added this
}
}
completion?(result) // <-- Added this call
})
task.resume()
}
func blockingGizlo() throws -> [String: Any]? // <-- Added this method
{
let sem = DispatchSemaphore(value: 1)
sem.wait()
var result: Result<[String: Any]?, Error>? = nil
gizlo {
result = $0
sem.signal()
}
sem.wait() // This wait will block until the closure calls signal
sem.signal() // Release the second wait.
switch result
{
case .success(let json) : return json
case .failure(let error) : throw error
case .none: fatalError("Unreachable")
}
}
}
let tr=test()
do {
let json = try tr.blockingGizlo()
print("\(json?.description ?? "nil")")
}
catch { print("Error: \(error.localizedDescription)") }
For some reason whenever I try to update my label with the current temperature using self.infoLabel.text = String(temp!) inside of the DispatchQueue code block, I get the following fatal error message:
unexpectedly found nil while unwrapping an Optional value.
I'd appreciate if someone could help me figure out why the code below isn't working. Thanks.
func getCurrentTemp(city: String){
let weatherRequestURL = URL(string: "\(openWeatherMapBaseURL)?APPID=\(openWeatherMapAPIKey)&q=\(city)")!
// The data task retrieves the data.
URLSession.shared.dataTask(with: weatherRequestURL) { (data, response, error) in
if let error = error {
// Case 1: Error
print("Error:\n\(error)")
}
else {
//print("Raw data:\n\(data!)\n")
//let dataString = String(data: data!, encoding: String.Encoding.utf8)
//print("Human-readable data:\n\(dataString!)")
do {
// Try to convert that data into a Swift dictionary
let weather = try JSONSerialization.jsonObject(with: data!, options:.allowFragments) as! [String:AnyObject]
if let main = weather["main"] as? [String: Any] {
let temp = main["temp"] as? Double
print("temp\(temp!)")
DispatchQueue.main.sync(execute: {
self.infoLabel.text = String(temp!)
})
//return temp as? String
//let temp_max = main["temp_max"] as? Double
//print("temp\(temp_max!)")
//let temp_min = main["temp_min"] as? Double
//print("temp\(temp_min!)")
}
}
catch let jsonError as NSError {
// An error occurred while trying to convert the data into a Swift dictionary.
print("JSON error description: \(jsonError.description)")
}
}
}
.resume()
}
There are two possibilities here: 1) either temp is nil (and it shouldn't be because you already force unwrap it in the print statement above) 2) or infoLabel is nil which happens if you broke your outlet connection.
Its easy to check; make a breakpoint above your assignment and in the debug console you can type:
po self.infoLabel
to see if its nil. For good measure you an also check temp.
You can also add a print statement to check self.infoLabel or an assert.
Alright, so I found a makeshift solution to this issue (See Below). Rather than placing the code inside of the function I made, I placed it in the viewDidLoad() function. For whatever reason, self.infoLabel? would be nil anywhere inside of the function I made.
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
print("Sucessful launched weather page.")
let weatherRequestURL = URL(string: "\(openWeatherMapBaseURL)?APPID=\(openWeatherMapAPIKey)&q=\(city)")!
// The data task retrieves the data.
URLSession.shared.dataTask(with: weatherRequestURL) { (data, response, error) in
if let error = error {
// Case 1: Error
print("Error:\n\(error)")
}
else {
//print("Raw data:\n\(data!)\n")
//let dataString = String(data: data!, encoding: String.Encoding.utf8)
//print("Human-readable data:\n\(dataString!)")
do {
// Try to convert that data into a Swift dictionary
let weather = try JSONSerialization.jsonObject(with: data!, options:.allowFragments) as! [String:AnyObject]
if let main = weather["main"] as? [String: Any] {
let temp = main["temp"] as? Double
print("temp\(temp!)")
var tempInFarenheit = ((9/5)*((temp!)-273) + 32).rounded()
DispatchQueue.main.sync(execute: {
self.infoLabel.text = "\(tempInFarenheit) + °"
})
}
}
catch let jsonError as NSError {
// An error occurred while trying to convert the data into a Swift dictionary.
print("JSON error description: \(jsonError.description)")
}
}
}
.resume()
}
Although this isn't the most effective way of doing things, hopefully it can help others who are having the same problem. If I find a more effective way of doing this, I'll be sure to edit this post and include it.
I have this simple code:
let task = session.dataTaskWithRequest(request, completionHandler: {(data, response, error) in
print(response)
do {
let JSON = try NSJSONSerialization.JSONObjectWithData(data!, options:.AllowFragments)
// never printed
print(JSON)
guard let JSONDictionary :NSDictionary = (JSON as! NSDictionary) else {
print("Not a Dictionary")
return
}
print("JSONDictionary! \(JSONDictionary)")
}
catch let JSONError as NSError {
print("\(JSONError)")
}
});
//
task.resume()
Well, I can read the response but then I get (lldb) and the app crashes. The line print(JSON) is never printed. I really can't understand what's going on, any tip is appreciated.
Your data is not JSON, it's JSONP (JSON with Padding). (see Wikipedia)
NSJSONSerialization cannot serialize JSONP.
Since try has failed, print(JSON) won't execute, and the code jumps to the catch block.