IOS: Detecting NSNull from JSON Not Working

Question

The following code designed to catch an NSNull in Json results is throwing an exception when the response is null.

 NSDictionary *jsonResults = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
    NSLog(@"jsonResults are:%@",jsonResults);
                if (![jsonResults isKindOfClass:[NSNull class]]&&!
[jsonResults[@"response"][@"insert_id"]isKindOfClass:[NSNull class]]&&!
(jsonResults==nil)){
    //do something
    }

When the exception occurs, the line beginning if (![json... is in green and the error message reads:

     Results: {
        code = 400;
        response = "0(NSNull)";
    }
    2016-05-26 07:18:06.327 idaru[385:60b] -[NSNull 
objectForKeyedSubscript:]: unrecognized selector sent to instance 
0x38871a70
    2016-05-26 07:18:06.329 myapp[385:60b] *** Terminating app due to 
uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull 
objectForKeyedSubscript:]: unrecognized selector sent to instance 
0x38871a70'

Can anyone suggest what could be wrong here?

Of note, I do have a category that supposedly converts NSNulls into 0s. Not sure how this interacts with above but here it is:

//NSNull+JSON.m
@implementation NSNull (JSON)

- (NSUInteger)length { return 0; }

- (NSInteger)integerValue { return 0; };

- (float)floatValue { return 0; };

- (NSString *)description { return @"0(NSNull)"; }

- (NSArray *)componentsSeparatedByString:(NSString *)separator { return @[]; }

- (id)objectForKey:(id)key { return nil; }

- (BOOL)boolValue { return NO; }

@end

Answer 1

Instead of [jsonResults isKindOfClass:[NSNull class]] you can simply do jsonResults == [NSNull null]

Answer 2

You are not checking if response is NSNull. My approach would be to test for what you want, not what you don't want:

NSDictionary *jsonResults = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
if (jsonResults) {    // This won't be NSNull, it will be nil on error
    NSDictionary *response = jsonResults[@"response"];
    if ([response isKindOfClass:[NSDictionary class]]) {
        NSNumber *insertId = response[@"insert_id"];    // Assumption
        if ([insertId isKindOfClass:[NSNumber class]]) {
            // Print value
        }
    }
} else {
    // Report error
}

In reality you need to know what values are optional and what values can be of different types, as you don't want to code the whole module using isKindOfClass.

Answer 3

try like this,

  if (![jsonResults isKindOfClass:[NSNull class]] || !(jsonResults==nil)) {

    if (![jsonResults[@"response"][@"insert_id"]isKindOfClass:[NSNull class]]) {

        //Do your task here
    }

}

It is because if your jsonResults is null then it can't check for [jsonResults[@"response"][@"insert_id"] !!

Update :

   if (!(jsonResults==nil)) {

    if (![jsonResults[@"response"][@"insert_id"]isKindOfClass:[NSNull class]]) {

        //Do your task here
    }

}

No need to check for NSNull for jsonResults. It only can be nil and objects contains by that jsonResults can be NSNull.

Hope this will help :)