ios check if nsarray == null

Question

I'm receiving some response from JSON, and is working fine, but I need to check for some null values,

I have found different answers but seems is not working still,

NSArray *productIdList = [packItemDictionary objectForKey:@"ProductIdList"];

I have tried with

if ( !productIdList.count )  //which breaks the app,

if ( productIdList == [NSNull null] )  // warning: comparison of distinct pointer types (NSArray and NSNull)

So what is happening? How to fix this and check for null in my array?

Thanks!

What do you mean “brakes the app”? If it's raising an exception, post the log messages. — rob mayoff
– rob mayoff, Commented Mar 1, 2012 at 6:05

rob mayoff · Accepted Answer · 2012-03-01 06:07:11Z

35

Eliminate the warning using a cast:

if (productIdList == (id)[NSNull null])

If productIdList is in fact [NSNull null], then doing productIdList.count will raise an exception because NSNull does not understand the count message.

answered Mar 1, 2012 at 6:07

rob mayoff

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2 Comments

Tommy Over a year ago

@MaKo ... and, implicitly, this works because [NSNull null] always returns the same object. == compares identity, not value.

Jean Over a year ago

I missed the cast to 'id' & was missing this check (ignored it due to compiler warning) for long time! thanks!

Nekto · Accepted Answer · 2012-03-01 06:16:54Z

7

You can also check class of an object by using method isKindOfClass:.

For example, in your case you could do following:

if ([productIdList isKindOfClass:[NSArray class]])
{
     // value is valid
}

or (if you are sure that NSNull is indicating invalid value)

if([productIdList isKindOfClass:[NSNull class]])
{
     // value is invalid
}

answered Mar 1, 2012 at 6:16

Nekto

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2 Comments

rob mayoff Over a year ago

There is only one singleton instance of NSNull so using == to check for it is shorter and more efficient.

Nekto Over a year ago

But checking type of returned object is more safely.

Charles Menguy · Accepted Answer · 2012-04-28 06:24:55Z

5

You can use the isEqual selector:

if ( [productIdList isEqual:[NSNull null]] )

edited Apr 28, 2012 at 6:24

Charles Menguy

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answered Apr 27, 2012 at 8:01

Devang

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Comments

scorpiozj · Accepted Answer · 2012-03-01 06:14:21Z

0

you should be clear what you want to check: the array is null which means the variable doesn't exist:


array == nil

Or the array has zero element which you can :


[array count] == 0

answered Mar 1, 2012 at 6:14

scorpiozj

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2 Comments

rob mayoff Over a year ago

The NSDictionary class cannot store nil as a value, so JSON parsers (and property list parsers) use [NSNull null] instead to represent a null value, because there is a difference between a key being present with a null value, and a key being absent.

Julian F. Weinert Over a year ago

The first line says all.

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