Found nil when unwrapping non nil value

Question

I'm trying to make a get request in swift passing the following parameters

var dict = [
    "id_struttura" : 2,
    "prenCheck" : [
        "codice" : "14:30_15:20_1_3831_0",
        "id_sport" : 6,
        "ora_fine" : "20/02/2015 15:20:00",
        "ora_inizio" : "20/02/2015 14:30:00",
        "rec" : 0,
        "soci" : [
            [
                "esterno" : 0,
                "id" : "1980"
            ],
            [
                "esterno" : 0,
                "id" : "51"
            ]
        ]
    ]
]

using the following method:

private func genericRequest(method: Methods, url: String, data: [String: AnyObject]?) -> AnyObject?{
    var getRequest : NSURLRequest?
    var postRequest : NSMutableURLRequest?

    if method == Methods.GET{
        var completeUrl = url

        if(data != nil){
            //println(data)
            completeUrl += "?"
            for (key, value) in data! {

                completeUrl += "\(key)=\(value)&"
            }
            completeUrl = completeUrl.substringToIndex(completeUrl.endIndex.predecessor())
        }
        //println(completeUrl)

        let url = NSURL(string: completeUrl)
        getRequest = NSURLRequest(URL: url!)

    }else if method == Methods.POST{
        postRequest = NSMutableURLRequest(URL: NSURL(string: url)!)
        var session = NSURLSession.sharedSession()
        postRequest!.HTTPMethod = "POST"

        var params : String = ""

        for (key, value) in data! {

            params += "\(key)=\(value)&"
        }
        params = params.substringToIndex(params.endIndex.predecessor())

        var err: NSError?
        postRequest!.HTTPBody = params.dataUsingEncoding(NSUTF8StringEncoding);
    }

    var response: NSURLResponse? = nil
    var error: NSError? = nil
    var request = getRequest != nil ? getRequest! : postRequest!
    let reply = NSURLConnection.sendSynchronousRequest(request, returningResponse:&response, error:&error)

    //println((response as NSHTTPURLResponse).statusCode)
    let results = NSString(data:reply!, encoding:NSUTF8StringEncoding)
    var json: AnyObject? = convertDataToJSON(reply)
    return json
}

calling it as genericRequest(Method.GET ,url:url, data: dict) (as Method is simply an enum) it can't unwrap the data variable in for (key,value)in data! when making a get request, but it can when it's making a post request. Since I have to use only get requests for this task (i'm dealing with a bad rest interface), could someone help me?

UPDATE: I also tried with if let data = data { ... and it crashes on this line saying unexpectedly found nil while unwrapping an Optional value

Answer 1

You are using a lot of force unwrapping ( ! ). Each place where you do that is a place where you are promising the compiler that the optional will never ever be nil. In most places I think that you should allow the compiler to prove the nil safety by using other methods of dealing with optionals (optional chaining, nil coalescing, map etc.)

In your specific case I don't know why you aren't doing:

if let data = data {

instead of:

if (data != nil) {

and then having to force unwrap data with ! .

I recently blogged and talked about the tools for dealing with optionals in Swift if you want more information about how not force unwrap.

Answer 2

Why you are not checking if data is nil in your POST method as you did in GET method. I think the post method is where you are trying to unwrap nil

if method == Methods.GET{
    var completeUrl = url

    // here you check if data is nil
    if(data != nil){
        //println(data)
        completeUrl += "?"
        for (key, value) in data! {

            completeUrl += "\(key)=\(value)&"
        }
        completeUrl = completeUrl.substringToIndex(completeUrl.endIndex.predecessor())
    }
    //println(completeUrl)

    let url = NSURL(string: completeUrl)
    getRequest = NSURLRequest(URL: url!)

}else if method == Methods.POST{
    postRequest = NSMutableURLRequest(URL: NSURL(string: url)!)
    var session = NSURLSession.sharedSession()
    postRequest!.HTTPMethod = "POST"

    var params : String = ""
    //check here as well
    if data != nil{
        for (key, value) in data! {

            params += "\(key)=\(value)&"
        }
        params = params.substringToIndex(params.endIndex.predecessor())
    }

    var err: NSError?
    postRequest!.HTTPBody = params.dataUsingEncoding(NSUTF8StringEncoding);
}