Checking a null value in Objective-C that has been returned from a JSON string

Question

I have a JSON object that is coming from a webserver.

The log is something like this:

{          
   "status":"success",
   "UserID":15,
   "Name":"John",
   "DisplayName":"John",
   "Surname":"Smith",
   "Email":"email",
   "Telephone":null,
   "FullAccount":"true"
}

Note the Telephone is coming in as null if the user doesn't enter one.

When assigning this value to a NSString, in the NSLog it's coming out as <null>

I am assigning the string like this:

NSString *tel = [jsonDictionary valueForKey:@"Telephone"];

What is the correct way to check this <null> value? It's preventing me from saving a NSDictionary.

I have tried using the conditions [myString length] and myString == nil and myString == NULL

Additionally where is the best place in the iOS documentation to read up on this?

Wevah · Accepted Answer · 2014-01-06 18:44:35Z

190

<null> is how the NSNull singleton logs. So:

if (tel == (id)[NSNull null]) {
    // tel is null
}

(The singleton exists because you can't add nil to collection classes.)

edited Jan 6, 2014 at 18:44

answered Jan 29, 2011 at 21:09

Wevah

28.2k7 gold badges86 silver badges74 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Aaron Hayman Over a year ago

If you want to do it without the cast, you can also try: if ([tel isKindOfClass:[NSNull class]])

Gajendrasinh Chauhan Over a year ago

we can use: if (object isEqual:[NSNull null]) {--logic here-- }

Flea · Accepted Answer · 2012-03-07 15:53:41Z

24

Here is the example with the cast:

if (tel == (NSString *)[NSNull null])
{
   // do logic here
}

answered Mar 7, 2012 at 15:53

Flea

11.3k6 gold badges76 silver badges88 bronze badges

1 Comment

Raphael Oliveira Over a year ago

or if (tel == (NSString *)NSNull.null) { // do logic here }

Nitin Gohel · Accepted Answer · 2013-05-27 07:23:48Z

10

you can also check this Incoming String like this way also:-

if(tel==(id) [NSNull null] || [tel length]==0 || [tel isEqualToString:@""])
{
    NSlog(@"Print check log");
}
else
{  

    NSlog(@Printcheck log %@",tel);  

}

edited May 27, 2013 at 7:23

answered Feb 6, 2013 at 5:10

Nitin Gohel

49.7k18 gold badges107 silver badges144 bronze badges

2 Comments

bdesham Over a year ago

Your first NSLog line is incorrect… it should say that the string is empty. And why would you print it in that case?

Nitin Gohel Over a year ago

thanks for advice and i print NSLog for just knowing which condition become true

P.J.Radadiya · Accepted Answer · 2016-08-03 13:03:21Z

9

If you are dealing with an "unstable" API, you may want to iterate through all the keys to check for null. I created a category to deal with this:

@interface NSDictionary (Safe)
-(NSDictionary *)removeNullValues;
@end

@implementation NSDictionary (Safe)

-(NSDictionary *)removeNullValues
{
    NSMutableDictionary *mutDictionary = [self mutableCopy];
    NSMutableArray *keysToDelete = [NSMutableArray array];
    [mutDictionary enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        if (obj == [NSNull null]) 
        {
            [keysToDelete addObject:key];
        }
    }];
    [mutDictinary removeObjectsForKeys:keysToDelete];
    return [mutDictinary copy];
}
@end

edited Aug 3, 2016 at 13:03

P.J.Radadiya

1,5391 gold badge12 silver badges21 bronze badges

answered Oct 16, 2013 at 17:50

Kyle C

4,0972 gold badges34 silver badges34 bronze badges

Comments

kjoelbro · Accepted Answer · 2013-12-13 09:09:32Z

4

The best answer is what Aaron Hayman has commented below the accepted answer:

if ([tel isKindOfClass:[NSNull class]])

It doesn't produce a warning :)

answered Dec 13, 2013 at 9:09

kjoelbro

6,3164 gold badges24 silver badges18 bronze badges

Comments

Brian · Accepted Answer · 2013-11-01 08:39:50Z

if you have many attributes in json, using if statement to check them one by one is troublesome. What even worse is that the code would be ugly and hard to maintain.

I think the better approach is creating a category of NSDictionary:

// NSDictionary+AwesomeDictionary.h

#import <Foundation/Foundation.h>

@interface NSDictionary (AwesomeDictionary)
- (id)validatedValueForKey:(NSString *)key;
@end

// NSDictionary+AwesomeDictionary.m

#import "NSDictionary+AwesomeDictionary.h"

@implementation NSDictionary (AwesomeDictionary)
- (id)validatedValueForKey:(NSString *)key {
    id value = [self valueForKey:key];
    if (value == [NSNull null]) {
        value = nil;
    }
    return value;
}
@end

after importing this category, you can:

[json validatedValueForKey:key];

Yunus Nedim Mehel · Accepted Answer · 2013-12-27 09:18:59Z

2

I usually do it like this:

Assuma I have a data model for the user, and it has an NSString property called email, fetched from a JSON dict. If the email field is used inside the application, converting it to empty string prevents possible crashes:

- (id)initWithJSONDictionary:(NSDictionary *)dictionary{

    //Initializer, other properties etc...

    id usersmail = [[dictionary objectForKey:@"email"] copy];
    _email = ( usersmail && usersmail != (id)[NSNull null] )? [usersmail copy] : [[NSString      alloc]initWithString:@""];
}

answered Dec 27, 2013 at 9:18

Yunus Nedim Mehel

12.4k4 gold badges54 silver badges57 bronze badges

Comments

Segev · Accepted Answer · 2014-11-17 19:15:44Z

2

In Swift you can do:

let value: AnyObject? = xyz.objectForKey("xyz")    
if value as NSObject == NSNull() {
    // value is null
    }

edited Nov 17, 2014 at 19:15

answered Nov 17, 2014 at 19:02

Segev

1,31716 silver badges21 bronze badges

2 Comments

JasonMArcher Over a year ago

Question is about Objective-C, not Swift.

Beau Nouvelle Over a year ago

@JasonMArcher The answer still provides some value for those coming to the question from a google search. It's a 4 year old question after all.

Marin Todorov · Accepted Answer · 2013-02-10 22:20:51Z

0

Best would be if you stick to best practices - i.e. use a real data model to read JSON data.

Have a look at JSONModel - it's easy to use and it will convert [NSNUll null] to * nil * values for you automatically, so you could do your checks as usual in Obj-c like:

if (mymodel.Telephone==nil) {
  //telephone number was not provided, do something here 
}

Have a look at JSONModel's page: http://www.jsonmodel.com

Here's also a simple walk-through for creating a JSON based app: http://www.touch-code-magazine.com/how-to-make-a-youtube-app-using-mgbox-and-jsonmodel/

answered Feb 10, 2013 at 22:20

Marin Todorov

6,3779 gold badges49 silver badges73 bronze badges

1 Comment

Stewart Macdonald Over a year ago

Does that JSONModel site still exist? It's not in English so I can't be sure, but it doesn't look like it has much to do with JSON.

user5930025 · Accepted Answer · 2016-02-15 12:48:07Z

0

I tried a lot method, but nothing worked. Finally this worked for me.

NSString *usernameValue = [NSString stringWithFormat:@"%@",[[NSUserDefaults standardUserDefaults] valueForKey:@"usernameKey"]];

if ([usernameValue isEqual:@"(null)"])
{
     // str is null
}

answered Feb 15, 2016 at 12:48

user5930025

Comments

Gajendrasinh Chauhan · Accepted Answer · 2016-02-18 06:11:59Z

0

if([tel isEqual:[NSNull null]])
{
   //do something when value is null
}

answered Feb 18, 2016 at 6:11

Gajendrasinh Chauhan

3,3728 gold badges42 silver badges56 bronze badges

1 Comment

Adnan Asghar Over a year ago

Generates a Warning: Incompatible pointer types sending 'NSNull * _Nonnull' to parameter of type 'Class'

Marwie · Accepted Answer · 2016-08-03 12:24:17Z

0

Try this:

if (tel == (NSString *)[NSNull null] || tel.length==0)
{
    // do logic here
}

edited Aug 3, 2016 at 12:24

Marwie

3,3473 gold badges31 silver badges54 bronze badges

answered Dec 27, 2013 at 12:37

Mritunjay

1676 bronze badges

Comments

Carles Estevadeordal · Accepted Answer · 2017-01-27 15:35:29Z

0

I use this:

#define NULL_TO_NIL(obj) ({ __typeof__ (obj) __obj = (obj); __obj == [NSNull null] ? nil : obj; })

answered Jan 27, 2017 at 15:35

Carles Estevadeordal

1,22911 silver badges21 bronze badges

2 Comments

Amr Angry Over a year ago

could you guide how we can achieve the same in swift?

Carles Estevadeordal Over a year ago

Hi @AmrAngry, I did not see your message, in swift there is a much better and sophisticated way to use response JSON objects using codable protocol on what is called a DTO: hackingwithswift.com/example-code/language/… Then you can get a struct or class with the objects you want, you can set coding keys so the variables do not have to have the same name than in the JSON object.

Chandni - Systematix · Accepted Answer · 2017-03-15 06:40:32Z

0

if we are getting null value like then we can check it with below code snippet.

 if(![[dictTripData objectForKey:@"mob_no"] isKindOfClass:[NSNull class]])
      strPsngrMobileNo = [dictTripData objectForKey:@"mobile_number"];
  else
           strPsngrMobileNo = @"";

answered Mar 15, 2017 at 6:40

Chandni - Systematix

1962 silver badges11 bronze badges

Comments

Rahul Narang · Accepted Answer · 2013-02-06 04:15:07Z

-6

Here you can also do that by checking the length of the string i.e.

if(tel.length==0)
{
    //do some logic here
}

answered Feb 6, 2013 at 4:15

Rahul Narang

3

2 Comments

Kurt Revis Over a year ago

No, if tel is an instance of NSNull, this will raise an exception.

Rahul Narang Over a year ago

yes i think we will have to check it's null or not also.We have to consider the above conditions also

Collectives™ on Stack Overflow

Checking a null value in Objective-C that has been returned from a JSON string

15 Answers 15

2 Comments

1 Comment

2 Comments

Comments

Comments

Comments

Comments

2 Comments

1 Comment

Comments

1 Comment

Comments

2 Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

15 Answers 15

2 Comments

1 Comment

2 Comments

Comments

Comments

Comments

Comments

2 Comments

1 Comment

Comments

1 Comment

Comments

2 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related