Retrieve empty array from Parse error

Question

In my app the user can view his own statistics. I retrieve an array from Parse like this:

...
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    userArray = [objects valueForKey:@"myArray"];
}];

The code works just fine when the array actually contains something... But if nothing is saved to the array in Parse.com I get errors..

Example: I run this code to test:

NSLog(@"%lu", (unsigned long)[[userArray objectAtIndex:0] count]);

When the array contains something it logs the correct number (works). But when the array is empty I get this error:

"-[NSNull count]: unrecognized selector sent to instance 0x199084fe0"

I can't figure out what is going on.. Anyone has an idea what is happening?

CrimsonChris · Accepted Answer · 2014-09-29 21:13:05Z

1

You're not getting an empty array, you are getting an NSNull. You can read more about the difference here.

Testing for NSNull is trivial. Consider replacing values that aren't NSArrays with nil.

id myArray = userArray.firstObject;
myArray = [myArray isKindOfClass:[NSArray class]] ? myArray : nil;
NSLog(@"%i", [myArray count]); //will log 0 because myArray is nil

edited Sep 29, 2014 at 21:13

answered Sep 29, 2014 at 21:01

CrimsonChris

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4 Comments

Peter Over a year ago

So what exactly is this doing? And how can it help me? I still get the same error..

Peter Over a year ago

Why wouldn't you just test if it is null? Like this:

id object = myArray[0];// similar to [myArray objectAtIndex:0]      if(![object isEqual:[NSNull null]])     {         //do something if object is not equals to [NSNull null]     }

CrimsonChris Over a year ago

I guess you could do that too if you prefer having conditional blocks in your code...

Peter Over a year ago

Could you take a look at my own answer to the question?

Peter · Accepted Answer · 2014-09-29 21:13:22Z

0

I found this code to help on my problem:

id object = userArray[0];

if([object isEqual:[NSNull null]]) {
    NSLog(@"Array is empty");
}

Is this safe to use?

answered Sep 29, 2014 at 21:13

Peter

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2 Comments

Peter Over a year ago

I'm obviously not as advanced as you, but I think I'll go for my solution for now.. But thanks anyway!

CrimsonChris Over a year ago

Also, this won't catch cases when you get something that isn't an NSNull. Like an NSDictionary or something else you aren't expecting. That's why I used isKindOfClass: to check if it's an NSArray.

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