User defaults gives nil value in Swift 3.0 - ios

Question

I am new to swift and trying to store NSMutableArray in Userdefaults. Here is what I am doinig :
//to save aaray in user defaults
var set:NSMutableArray = NSMutableArray(objects: self.listId)
self.saveListIdArray(set)
func saveListIdArray(_ params: NSMutableArray = []) {
let defaults = UserDefaults.standard
defaults.set(params, forKey: "ArrayKey")
defaults.synchronize()
}
//to get array from user default
func getUserDefaultKeyForAllObject(key userDefaultsKey: String) -> NSMutableArray {
let array = UserDefaults.standard.object(forKey: NSUserDefaultsKey.LIST_ID_ARRAY) as! NSMutableArray
print(array)
return array
}
App crashes with "fatal error: unexpectedly found nil while unwrapping an Optional value" exception.
Ignore the way I ask the question, help me out here.
Thank you.

Answer 1

Try converting to NSData then storing to nsuserdefaults like below
func saveListIdArray(_ params: NSMutableArray = []) {
let data = NSKeyedArchiver.archivedData(withRootObject: params)
UserDefaults.standard.set(data, forKey: "test")
UserDefaults.standard.synchronize()
}
For retrieving the data use
if let data = UserDefaults.standard.object(forKey: "test") as? Data {
if let storedData = NSKeyedUnarchiver.unarchiveObject(with: data) as? NSMutableArray
{
// In here you can access your array
}
}

Answer 2

You are force unwrapping the NSMutableArray for a key. Don't force unwrap when you try to get the value from a dictionary or UserDefault for a key because there may be a chance that the value does not exist for that key and force unwrapping will crash your app.
Do this as:
//to get array from user default
if let array = UserDefaults.standard.object(forKey:"ArrayKey") as? NSMutableArray
print(array)
}

Answer 3

I have 2 possible reasons for this:
You need to be 100% sure that you are retrieving array with the same key as you save it with. In your code you are saving the array with "ArrayKey" but retrieving it with NSUserDefaultsKey.LIST_ID_ARRAY, are you sure this is the same string?
What datatype is self.listId? If it's a custom class then you need to make that class conform to the nscoding protocol, then encode it to Data and save that to the userDefaults (Save custom objects into NSUserDefaults)
A 3rd reason is that you are trying to get an object from the defaults without ever writing anything to it. Try changing
let array = UserDefaults.standard.object(forKey: NSUserDefaultsKey.LIST_ID_ARRAY) as! NSMutableArray
print(array)
return array
to
if let array = UserDefaults.standard.object(forKey: "ArrayKey") as? NSMutableArray {
print(array)
return array
}
else {
return NSMutableArray()
}