How to check if an NSDictionary or NSMutableDictionary contains a key

Question

I need to check if an dict has a key or not  How

User · Answer

Solution for swift 4 2  So  if you just want to answer the question whether the dictionary contains the key  ask   let keyExists   dict key     nil   If you want the value and you know the dictionary contains the key  say   let val   dict key     But if  as usually happens  you don t know it contains the key - you want to fetch it and use it  but only if it exists - then use something like if let   if let val   dict key           now val is not nil and the Optional has been unwrapped  so use it

User · Answer

if   MyDictionary objectForKey MyKey               Key Exist

User · Answer

One very nasty gotcha which just wasted a bit of my time debugging - you may find yourself prompted by auto-complete to try using doesContain which seems to work   Except  doesContain uses an id comparison instead of the hash comparison used by objectForKey so if you have a dictionary with string keys it will return NO to a doesContain   NSMutableDictionary  keysByName     NSMutableDictionary alloc  init   keysByName   fred      1  NSString  test     fred    if   keysByName objectForKey test     nil      NSLog    nit works for key lookups        OK else     NSLog    nsod it     if  keysByName test     nil      NSLog    nit works for key lookups using indexed syntax        OK else     NSLog    nsod it     if   keysByName doesContain   fred        NSLog    n doesContain works literally    else     NSLog    nsod it        this one fails because of id comparison used by doesContain

User · Answer

if    dictionary   quot data quot     quot action quot   isKindOfClass NSNull class           do something if doesn t exist    This is for nested dictionary structure

User · Answer

Using Swift  it would be   if myDic KEY     nil          key exists

User · Answer

objectForKey will return nil if a key doesn t exist

User · Answer

I d suggest you store the result of the lookup in a temp variable  test if the temp variable is nil and then use it  That way you don t look the same object up twice    id obj    dict objectForKey   blah     if  obj          use obj   else         Do something else

User · Answer

if    dictionary allKeys  containsObject key            contains key     or  if   dictionary objectForKey key            contains object

User · Answer

if   mydict objectForKey   mykey             key exists    else

User · Answer

As Adirael suggested objectForKey to check key existance but When you call objectForKeyin nullable dictionary  app gets crashed so I fixed this from following way   -  instancetype initWithDictionary  NSDictionary  dictionary   id object   dictionary   if  dictionary  amp  amp   object     NSNull null          self name    dictionary objectForKey   name        self age    dictionary objectForKey   age      return self

User · Answer

For checking existence of key in NSDictionary     if  dictionary objectForKey   Replace your key here      nil      NSLog   Key Exists    else     NSLog   Key not Exists

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When using JSON dictionaries    define isNull value  value    nil     value isKindOfClass  NSNull class    if  isNull  dict   my key                do stuff

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I like Fernandes  answer even though you ask for the obj twice    This should also do  more or less the same as Martin s A    id obj   if   obj  dict objectForKey   blah             use obj   else         Do something else like creating the obj and add the kv pair to the dict     Martin s and this answer both work on iPad2 iOS 5 0 1 9A405

User · Answer

More recent versions of Objective-C and Clang have a modern syntax for this   if  myDictionary myKey          You do not have to check for equality with nil  because only non-nil Objective-C objects can be stored in dictionaries or arrays   And all Objective-C objects are truthy values  Even  NO   0  and  NSNull null  evaluate as true    Edit  Swift is now a thing    For Swift you would try something like the following  if let value   myDictionary myKey         This syntax will only execute the if block if myKey is in the dict and if it is then the value is stored in the value variable  Note that this works for even falsey values like 0

User · Answer

Yes  This kind of errors are very common and lead to app crash  So I use to add NSDictionary in each project as below      h file code     interface NSDictionary  AppDictionary   -  id objectForKeyNotNull    id key    end      m file code is as below   import  NSDictionary WKDictionary h    implementation NSDictionary  WKDictionary    -  id objectForKeyNotNull  id key        id object    self objectForKey key       if  object     NSNull null        return nil       return object       end   In code you can use as below   NSStrting  testString    dict objectForKeyNotNull   blah

User · Answer

Because nil cannot be stored in Foundation data structures NSNull is sometimes to represent a nil  Because NSNull is a singleton object you can check to see if NSNull is the value stored in dictionary by using direct pointer comparison   if   NSNull    user objectForKey   myKey       NSNull null

[objective-c] How to check if an NSDictionary or NSMutableDictionary contains a key?

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