How can I check if an object in an NSArray is NSNull?

Question

I am getting an array with null value. Please check the structure of my array below:

 (
    \"< null>\"
 )

When I\'m trying to access

Answer 1

Consider this approach:

Option 1:

NSString *str = array[0];

if ( str != (id)[NSNull null] && str.length > 0 {
    // you have a valid string.
} 

Option 2:

NSString *str = array[0];
str = str == (id)[NSNull null]? nil : str;

if (str.length > 0) {
   // you have a valid string.
} 

Answer 2

id object = myArray[0];// similar to [myArray objectAtIndex:0]

if(![object isEqual:[NSNull null]])
{
    //do something if object is not equals to [NSNull null]
}

Answer 3

if (myArray != (id)[NSNull null])

OR

if(![myArray isKindOfClass:[NSNull class]]) 

Answer 4

You can use the following check:

if (myArray[0] != [NSNull null]) {
    // Do your thing here
}

The reason for this can be found on Apple's official docs:

Using NSNull

The NSNull class defines a singleton object you use to represent null values in situations where nil is prohibited as a value (typically in a collection object such as an array or a dictionary).

NSNull *nullValue = [NSNull null];
NSArray *arrayWithNull = @[nullValue];
NSLog(@"arrayWithNull: %@", arrayWithNull);
// Output: "arrayWithNull: (<null>)"

It is important to appreciate that the NSNull instance is semantically different from NO or false—these both represent a logical value; the NSNull instance represents the absence of a value. The NSNull instance is semantically equivalent to nil, however it is also important to appreciate that it is not equal to nil. To test for a null object value, you must therefore make a direct object comparison.

id aValue = [arrayWithNull objectAtIndex:0];
if (aValue == nil) {
    NSLog(@"equals nil");
}
else if (aValue == [NSNull null]) {
    NSLog(@"equals NSNull instance");
    if ([aValue isEqual:nil]) {
        NSLog(@"isEqual:nil");
    }
}
// Output: "equals NSNull instance"

Taken from https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/NumbersandValues/Articles/Null.html

Answer 5

I found the code for working with NSNull has the following problems:

• Looks noisy and ugly.
• Time consuming.
• Error prone.

So I created the following category:

@interface NSObject (NSNullUnwrapping)

/**
* Unwraps NSNull to nil, if the object is NSNull, otherwise returns the object.
*/
- (id)zz_valueOrNil;

@end

With the implementation:

@implementation NSObject (NSNullUnwrapping)

- (id)zz_valueOrNil
{
    return self;
}

@end

@implementation NSNull (NSNullUnwrapping)

- (id)zz_valueOrNil
{
    return nil;
}

@end

It works by the following rules:

• If a category is declared twice for the same Class (ie singleton instance of the Class type) then behavior is undefined. However, a method declared in a subclass is allowed to override a category method in its super-class.

This allows for more terse code:

[site setValue:[resultSet[@"main_contact"] zz_valueOrNil] forKey:@"mainContact"];

. . as opposed to having extra lines to check for NSNull. The zz_ prefix looks a little ugly but is there for safety to avoid namespace collisions.

Answer 6

Building off of Toni's answer I made a macro.

#define isNSNull(value) [value isKindOfClass:[NSNull class]]

Then to use it

if (isNSNull(dict[@"key"])) ...