Alamofire在展开Optional值时意外发现nil

Question

I use this Alamofire code to download images for URL

func getImage(imageUrlString: String, completionHandler: (responseObject: UIImage?, error: NSError?) -> ()) {
        makeGetImageCall(imageUrlString, completionHandler: completionHandler)
    }

    func makeGetImageCall(imageUrlString: String, completionHandler: (responseObject: UIImage?, error: NSError?) -> ()) {
        //Perform request
        print("Trying to get: " + imageUrlString)
        Alamofire.request(.GET, imageUrlString, headers: ["Authorization": NSUserDefaults.standardUserDefaults().stringForKey("BasicAuthenticationString")!])
            .responseImage { request, response, result in
                print(request)
                print(response)
                print(result)
                completionHandler(responseObject: result.value, error: nil)
        }
    }

This is my class that uses the method:

public class NewsListEntry: NSObject {
    public var thumbnail: String = ""
    public var thumbnailImage: UIImage = UIImage()
    public var thumbnailDownloaded: Bool = false


    public func downloadThumbnail() {
        print(self.title)
        GetImageHandeler().getImage(self.thumbnail, completionHandler: { (responseObject, error) in
        })
    }
}

Then i get a:

fatal error: unexpectedly found nil while unwrapping an Optional value

What have i done wrong?

This is the errors im getting:

Answer 1

What have i done wrong?

Two things. First, you are using the force-unwrap operator somewhere, possibly here:

NSUserDefaults.standardUserDefaults().stringForKey("BasicAuthenticationString")!

This means you're guaranteeing that the return value isn't nil , but in this case, it was. Since you broke your promise, the app crashes.

Second, PLEASE DO NOT STORE AUTHORIZATION STRINGS IN NSUSERDEFAULTS . iOS has a highly secure keychain for a reason. NSUserDefaults provides no encryption. Please use the keychain. There are wrapper libraries like Locksmith and SSKeychain which can help you.

Answer 2

You are unwrapping the result without checking if it's valid or not. Add the following code:

Alamofire.request(.GET, imageUrlString, headers: ["Authorization": NSUserDefaults.standardUserDefaults().stringForKey("BasicAuthenticationString")!])
    .responseImage { request, response, result in
        print(request)
        print(response)
        print(result)
        switch result {
        case .Success(let value):
            completionHandler(responseObject: value, error: nil)
        case .Failure(_, let error):
            completionHandler(responseObject: nil, error: error)
        }
}

If using Swift 2, you'll need to change the error parameter of the completionHandler block from NSError? to ErrorType .