Swift: Escaping closure captures non-escaping parameter 'onCompletion' - ios

Question

I have a problem with my swift. I am trying to send an API request and then retrieve data but I get the following error message:
"Swift: Escaping closure captures non-escaping parameter 'onCompletion'".
Does anyone know how I can solve this? thanks in advance
Code:
class RestApiManager: NSObject {
static let sharedInstance = RestApiManager()
let baseURL = "http://api.randomuser.me/"
func getRandomUser(onCompletion : (JSON) -> Void) {
makeHTTPGetRequest(path: baseURL, onCompletion: { json, err -> Void in
onCompletion(json)
})
}
func makeHTTPGetRequest(path: String, onCompletion: ServiceResponse) {
let request = NSMutableURLRequest(url : URL(string: path)! as URL)
let session = URLSession.shared
let task = session.dataTask(with: request as URLRequest, completionHandler: { data, response, error in
let json:JSON = JSON(data as Any)
onCompletion(json, error as NSError?)
})
task.resume()
}
}

Answer 1

You have to mark both completion handlers with #escaping. Usually the compiler offers a fix
class RestApiManager: NSObject {
static let sharedInstance = RestApiManager()
let baseURL = "http://api.randomuser.me/"
func getRandomUser(onCompletion : #escaping (JSON) -> Void) {
makeHTTPGetRequest(path: baseURL, onCompletion: { json, err -> Void in
onCompletion(json)
})
}
func makeHTTPGetRequest(path: String, onCompletion: #escaping ServiceResponse) {
let request = NSMutableURLRequest(url : URL(string: path)! as URL)
let session = URLSession.shared
let task = session.dataTask(with: request as URLRequest, completionHandler: { data, response, error in
let json:JSON = JSON(data as Any)
onCompletion(json, error as NSError?)
})
task.resume()
}
}

Answer 2

Answers here were right on adding #escaping before the completion handler parameter declaration, albeit shortly explained.
Here's what I was missing for the full picture, taken from Swift's documentation:
Escaping Closures
A closure is said to escape a function when the
closure is passed as an argument to the function, but is called after
the function returns. When you declare a function that takes a closure
as one of its parameters, you can write #escaping before the
parameter’s type to indicate that the closure is allowed to escape.
So basically, if you want a completion handler to be called AFTER the method returns, it is defined as escaping in swift, and should be declared as such:
func makeHTTPGetRequest(path: String, onCompletion: #escaping ServiceResponse)

Answer 3

This is happning due to your parameter onCompletion. By default it is #nonesacping you have to marke it #esacping so it can be worked in completionHandler closure.
func makeHTTPGetRequest(path: String, onCompletion: #escaping ServiceResponse)

Answer 4

Use this:
class RestApiManager: NSObject {
static let sharedInstance = RestApiManager()
let baseURL = "http://api.randomuser.me/"
func getRandomUser(onCompletion : #escaping (JSON) -> Void) {
makeHTTPGetRequest(path: baseURL, onCompletion: { json, err -> Void in
onCompletion(json)
})
}
func makeHTTPGetRequest(path: String, onCompletion: #escaping ServiceResponse) {
let request = NSMutableURLRequest(url : URL(string: path)! as URL)
let session = URLSession.shared
let task = session.dataTask(with: request as URLRequest, completionHandler: { data, response, error in
let json:JSON = JSON(data as Any)
onCompletion(json, error as NSError?)
})
task.resume()
}
}