致命错误：在展开Optional值时意外发现nil，获取json错误swift

Question

Get json error

I am getting the error fatal error: unexpectedly found nil while unwrapping an Optional value when I try to return the json :

func getJson (str:NSString) -> AnyObject{

    var proxiesURL = NSURL(string:str)
    var proxiesDataJson = NSData.dataWithContentsOfURL(proxiesURL, options: NSDataReadingOptions.DataReadingUncached, error: nil)
    var json: AnyObject!

    if (proxiesDataJson != nil ){
        json = NSJSONSerialization.JSONObjectWithData(proxiesDataJson, options: NSJSONReadingOptions.AllowFragments, error: nil) as AnyObject
    }
    return json
}

Answer 1

I assume the question is "what am I doing wrong".

Your function returns AnyObject (non-optional, thus cannot be nil). You declared json as AnyObject! (implicitly unwrapped optional - it may be nil, but you promise to compiler that it will have non-nil value). And yet json is nil when you attempt to return it - either code at json = NSJSONSerialization.JSONObjectWithData line wasn't executed, or NSJSONSerialization.JSONObjectWithData returned nil.

Answer 2

You used ! with optional object which should be used only when you have checked its not nil, else it will crash. Instead you should wrap it with ? instead of !. It won't crash and you don't have to check for nil.