NSUserDefaults - How to tell if a key exists

Question

I m working on a small iPhone app  and I am using NSUserDefaults as my data persistence   It only has to keep track of a few things  such as some names and some numbers so I figure I might as well keep it simple   I found this page for some reference  but I don t think it can answer my question   Basically  I want to be able to check if a value  or a key  already exists in the NSUserDefaults and then do something accordingly   Some examples  The app starts up  if this is the first time it starts up it outputs an alert saying welcome   To tell if this is first time it has opened it reads the UserDefaults and checks   Example 2   It says   Hello  Name    where Name is something you have entered   If you have opened the app and there is no name  it should say  Hello World    I need to check if you have entered a name already and act accordingly   The name would be stored in NSUserDefaults   Some help here   I d really appreciate it

User · Answer

I just went through this  and all of your answers helped me toward a good solution  for me  I resisted going the route suggested by  just because I found it hard to read and comprehend   Here s what I did  I had a BOOL being carried around in a variable called   talkative    When I set my default  NSUserDefaults  object  I set it as an object  as I could then test to see if it was nil     converting BOOL to an object so we can check on nil  defaults setObject    talkative  forKey   talkative      Then when I went to see if it existed  I used   if   defaults objectForKey   talkative    nil         Then I used the object as a BOOL   if   defaults boolForKey   talkative             This seems to work in my case  It just made more visual sense to me

User · Answer

objectForKey will return nil if it doesn t exist    It will also return nil if it does exist and it is either an integer or a boolean with a value of zero  i e  FALSE or NO for the boolean    I ve tested this in the simulator for both 5 1 and 6 1   This means that you cannot really test for either integers or booleans having been set by asking for  the object    You can get away with this for integers if you don t mind treating  not set  as if it were  set to zero    The people who already tested this appear to have been fooled by the false negative aspect  i e  testing this by seeing if objectForKey returns nil when you know the key hasn t been set but failing to notice that it also returns nil if the key has been set but has been set to NO   For my own problem  that sent me here  I just ended up changing the semantics of my boolean so that my desired default was in congruence with the value being set to NO   If that s not an option  you ll need to store as something other than a boolean and make sure that you can tell the difference between YES  NO  and  not set

User · Answer

Swift version to get Bool   NSUserDefaults standardUserDefaults   objectForKey DefaultsIsGiver  as  Bool

User · Answer

The objectForKey  method will return nil if the value does not exist  Here s a simple IF   THEN test that will tell you if the value is nil   if   NSUserDefaults standardUserDefaults  objectForKey   YOUR KEY      nil

User · Answer

objectForKey  will return nil if it doesn t exist

User · Answer

Swift 3   4   Here is a simple extension for Int Double Float Bool key-value types that mimic the Optional-return behavior of the other types accessed through UserDefaults    Edit Aug 30 2018  Updated with more efficient syntax from Leo s suggestion    extension UserDefaults           Convenience method to wrap the built-in  integer forKey   method in an optional returning nil if the key doesn t exist      func integerOptional forKey  String  - gt  Int            return self object forKey  forKey  as  Int               Convenience method to wrap the built-in  double forKey   method in an optional returning nil if the key doesn t exist      func doubleOptional forKey  String  - gt  Double            return self object forKey  forKey  as  Double               Convenience method to wrap the built-in  float forKey   method in an optional returning nil if the key doesn t exist      func floatOptional forKey  String  - gt  Float            return self object forKey  forKey  as  Float               Convenience method to wrap the built-in  bool forKey   method in an optional returning nil if the key doesn t exist      func boolOptional forKey  String  - gt  Bool            return self object forKey  forKey  as  Bool           They are now more consistent alongside the other built-in get methods  string  data  etc    Just use the get methods in place of the old ones   let AppDefaults   UserDefaults standard     assuming the key  Test  does not exist        old  print AppDefaults integer forKey   Test          0    new  print AppDefaults integerOptional forKey   Test          nil

User · Answer

Swift 3 0     if NSUserDefaults standardUserDefaults   dictionaryRepresentation   contains    0 0     Your Comparison Key                          result   NSUserDefaults standardUserDefaults   objectForKey self ticketDetail ticket id  as  String

User · Answer

Try this little crumpet   - void saveUserSettings  NSNumber    value   value    NSNumber numberWithFloat self sensativity     NSUserDefaults standardUserDefaults  setObject value forKey   sensativity      - void loadUserSettings      NSNumber    value      value     NSUserDefaults standardUserDefaults  objectForKey   sensativity        if value    nil           self sensativity   4 0       else          self sensativity    value floatValue             Treat everything as an object   Seems to work for me

User · Answer

Extend UserDefaults once to don t copy-paste this solution   extension UserDefaults        func hasValue forKey key  String  - gt  Bool           return nil    object forKey  key              Example UserDefaults standard hasValue forKey   username

User · Answer

As mentioned above it wont work for primitive types where 0 NO could be a valid value  I am using this code   NSUserDefaults  defaults   NSUserDefaults standardUserDefaults   if    defaults dictionaryRepresentation  allKeys  containsObject   mykey          NSLog   mykey found

User · Answer

In Swift3  I have used in this way  var hasAddedGeofencesAtleastOnce  Bool       get           return UserDefaults standard object forKey   hasAddedGeofencesAtleastOnce      nil           The answer is great if you are to use that multiple times   I hope it helps

[ios] NSUserDefaults - How to tell if a key exists

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