canEvaluatePolicy Extra argument 'error' in call Swift Xcode 7 - ios

Question

I work with Xcode 7 with swift and I would use the Touch Id. Only I have a error when I use canEvaluatePolicy. I understand my error, I call an argument too. Only if I do not call, it makes me a error because I did not manage my error ...
Here are my error and my code:
PS: sorry for my bad English.
Error : Extra argument 'error' in call
or
Error : Call can throw, but it is not marked with 'try' and the error is not handled
My code :
import Foundation
import UIKit
import LocalAuthentication
class touchid : UIViewController, CLLocationManagerDelegate {
#IBOutlet weak var lblTouchId: UILabel!
override func viewDidLoad() {
self.view.addGestureRecognizer(self.revealViewController().panGestureRecognizer())
}
#IBAction func authenticateWithTouchID(sender: AnyObject) {
let authenticationObject = LAContext()
self.pleaseWait()
if authenticationObject.canEvaluatePolicy(.DeviceOwnerAuthenticationWithBiometrics) {
authenticationObject.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: "Access", reply: {(Bool, authenticationError) in
if authenticationError != nil {
// Authentification annulé ou Touch id non disponible
self.lblTouchId.text = "annulé ou touch id non disponible"
self.clearAllNotice()
self.errorNotice("Erreur !")
}
else {
if Bool == true {
self.lblTouchId.text = "authentification réussi"
self.clearAllNotice()
self.successNotice("Succès !")
}
else {
self.lblTouchId.text = "echec de l'authentification"
self.clearAllNotice()
self.errorNotice("Erreur !")
}
}
}
)
}
}
}

Answer 1

As mentioned in Using Swift with Cocoa and Objective-C, all Objective-C methods that use NSError to return an error object will now throw when called from Swift 2.0, so you need to use:
do {
try method()
} catch let error as NSError {
reportError(error)
}
Removing the reference to NSError in the method() call.

Answer 2

Looking at Apple's documentation, something seems off. The method signature is:
func canEvaluatePolicy(_ policy: LAPolicy, error error: NSErrorPointer) -> Bool
The odd part is that currently, the method doesn't throw anything, so putting it in a do-try block isn't necessary. I don't know if (but my guess is that yes) this framework is still getting tweaked with Swift 2.0, but I thought I remembered it implementing throw at one point in the Xcode/Swift beta iterations. At one point the compiler was acting a little wonky and said that:
1 - the method signature only had 1 parameter, but implements throws (which it doesn't)
2 - But as mentioned above, when you do that, the compiler then gives you different errors.
One thing to point out is that the current method signature, as of this writing, has a second parameter which is an NSErrorPointer, not an NSError? object. Treat it like the current Apple docs suggest, so add something like:
var error: NSErrorPointer?
let canEvaluatePolicty = LAContext().canEvaluatePolicy(.DeviceOwnerAuthenticationWithBiometrics, error: error!)
And your code should compile. It might be a good idea to keep an eye on this framework as more iterations of the beta's come out.
Good Luck!

Answer 3

Although the answer from g_blott does indeed compile, it's not good practice to force unwrap when you're not sure what could happen.
This code also compiles, but doesn't force unwrap anything and handles the existence of an error:
var error: NSError?
let errorPointer: NSErrorPointer = NSErrorPointer(&error)
let canEvaluate = context.canEvaluatePolicy(.deviceOwnerAuthentication, error: errorPointer)
if let error = error {
print("Oh noes, an error! ", error)
} else if canEvaluate {
print("Can evaluate")
} else {
print("Can't evaluate")
}