如果NSUserDefaults返回nil，则应用程序崩溃

Question

I have a situation where key values from NSUserDefaults memory shall be displayed(restored) on pre-view in a storyboard but they are stored(saved) only in the next view controller following the view where they shall be restored. In case nothing is stored (such as when the app is run for the first time), the app crashes with error as follows when i try to run view with the store key involved.

fatal error: unexpectedly found nil while unwrapping an Optional value

Further, the NSUserDefaults are part of switch statement on this pre-view as follows. Is there anyway to tell system that if store of the key is nil, please display 0. I think it is specifics of Swift, but not clear how to syntax it in this situation. Appreciate help.

var dummy: DummyTest! = nil
switch self.lessonNumber {
case 1:
    NSUserDefaults.standardUserDefaults().setObject(self.score, forKey: "storedDummyEssentialsPoints")
case 2:
    NSUserDefaults.standardUserDefaults().setObject(self.score, forKey: "storedDummyFoodPoints")
case 3:
    NSUserDefaults.standardUserDefaults().setObject(self.score, forKey: "storedDummyNumbersPoints")

...

Answer 1

Check whether NSUserDefaults value contain any value or not.If not, then set value as:

var str: AnyObject? = NSUserDefaults.standardUserDefaults().objectForKey("storedDummyEssentialsPoints")
if (str == nil )
{
    NSUserDefaults.standardUserDefaults().setObject(self.score, forKey:  "storedDummyEssentialsPoints")
}

Answer 2

Use if let will be able to check whether your object is nil.

    if let score: AnyObject = NSUserDefaults.standardUserDefaults().objectForKey("storedDummyEssentialsPoints") {
        println("\(score)")
    }
    // is nil
    else {
        NSUserDefaults.standardUserDefaults().setObject(self.score, forKey: "storedDummyEssentialsPoints")
        NSUserDefaults.standardUserDefaults().synchronize()
    }