Invalid conversion from throwing function of type (_,_,_) throws -> Void to non-throwing function type (NSData?, NSURLResponse?, NSError?) -> Void
IosSwiftTry CatchUrlsessionJson SerializationIos Problem Overview
I have written this code:
func getjson() {
let urlPath = "https://api.whitehouse.gov/v1/petitions.json?limit=100"
let url = NSURL(string: urlPath)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithURL(url!, completionHandler: {data, response, error -> Void in
print("Task completed")
if(error != nil) {
print(error!.localizedDescription)
}
let err: NSError?
if let jsonResult = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers) as? NSDictionary {
if(err != nil) {
print("JSON Error \(err!.localizedDescription)")
}
if let results: NSArray = jsonResult["results"] as? NSArray {
dispatch_async(dispatch_get_main_queue(), {
self.tableData = results
self.Indextableview.reloadData()
})
}
}
})
task.resume()
}
And after update to XCode 7 it gives me this error: Invalid conversion from throwing function of type (_, _, _) throws -> Void to non-throwing function type (NSData?, NSURLResponse?, NSError?) -> Void. It is in line, where is let task.
Thanks
Ios Solutions
Solution 1 - Ios
You need to implement Do Try Catch error handling as follow:
import UIKit
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true
extension URL {
func asyncDownload(completion: @escaping (_ data: Data?, _ response: URLResponse?, _ error: Error?) -> ()) {
URLSession.shared
.dataTask(with: self, completionHandler: completion)
.resume()
}
}
let jsonURL = URL(string: "https://api.whitehouse.gov/v1/petitions.json?limit=100")!
let start = Date()
jsonURL.asyncDownload { data, response, error in
print("Download ended:", Date().description(with: .current))
print("Elapsed Time:", Date().timeIntervalSince(start), terminator: " seconds\n")
print("Data size:", data?.count ?? "nil", terminator: " bytes\n\n")
guard let data = data else {
print("URLSession dataTask error:", error ?? "nil")
return
}
do {
let jsonObject = try JSONSerialization.jsonObject(with: data)
if let dictionary = jsonObject as? [String: Any],
let results = dictionary["results"] as? [[String: Any]] {
DispatchQueue.main.async {
results.forEach { print($0["body"] ?? "", terminator: "\n\n") }
// self.tableData = results
// self.Indextableview.reloadData()
}
}
} catch {
print("JSONSerialization error:", error)
}
}
print("\nDownload started:", start.description(with: .current))
Solution 2 - Ios
As Leo suggested, your problem is that you're using try
, but not within the do
-try
-catch
construct, which means that it infers that the closure is defined to throwing the error, but since it is not defined as such, you get that error.
So, add do
-try
-catch
:
func getjson() {
let urlPath = "https://api.whitehouse.gov/v1/petitions.json?limit=100"
let url = URL(string: urlPath)!
let session = URLSession.shared
let task = session.dataTask(with: url) { data, response, error in
print("Task completed")
guard let data = data, error == nil else {
print(error?.localizedDescription)
return
}
do {
if let jsonResult = try JSONSerialization.jsonObject(with: data) as? [String: Any] {
if let results = jsonResult["results"] as? [Any] {
DispatchQueue.main.async {
self.tableData = results
self.indexTableView.reloadData()
}
}
}
} catch let parseError {
print("JSON Error \(parseError.localizedDescription)")
}
}
task.resume()
}
Solution 3 - Ios
In Swift 2, replace all NSError
with ErrorType
Try this.
class func fetchWeatherForLocation(locationCode: String = "", shouldShowHUD: Bool = false, completionHandler: (data: NSDictionary?, error: ErrorType?) -> ()) {
let url = NSURL(string: "myurl")
let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data, response, error) in
if let dataWithKey = data {
do {
let jsonForDataWithTemprature = try NSJSONSerialization.JSONObjectWithData(dataWithKey, options:NSJSONReadingOptions.MutableContainers)
guard let arrayForDataWithKey :NSArray = jsonForDataWithTemprature as? NSArray else {
print("Not a Dictionary")
return
}
let dictionaryWithTemprature = arrayForDataWithKey.firstObject as! NSDictionary
completionHandler(data: dictionaryWithTemprature, error: nil)
}
catch let JSONError as ErrorType {
print("\(JSONError)")
}
}
}
task.resume()
}
Solution 4 - Ios
Changing the error type in the code try-catch worked for me.
"replace all NSError with ErrorType"