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\",
   \"Us         


        

Answer 1

<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.)

Answer 2

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/

Answer 3

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

Answer 4

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
}

Answer 5

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);  

}

Answer 6

Here is the example with the cast:

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