CODEWITHSUNDEEP
iphoneobjective-c
user440096
user440096

Reputation:

NSString contains : <null> and is crashing my app

I've an NSString thats populated from some data returned via JSON.

The code works great under normal circumstances but there is an occasion when i get returned by the JSON.

When i do a check to see if my NSString == nil or == null it fails the test.

But the fact that the NSString contains crashes my app.

So does have some special meaning in Objective C? Or should i just do a string compare and see if the string is equal to rather than being nil and handle it that way.

This has me a little confused.

Many Thanks, Code

Upvotes: 3

Views: 2969

Answers (4)

Lyubomir Marinov
Lyubomir Marinov

Reputation: 1

I did it this way:

if([string isKindOfClass:[NSNull class]]) {
    NSLog(@"This is JSON null");
} else {
    NSLog(@"This is a string, do what you wanna do with it");
}

Upvotes: 0

user456236
user456236

Reputation:

You could check to see if it's null by.

if ([str isKindOfClass:[NSNull class]]) {
   // str is null.
}

Upvotes: 2

Wevah
Wevah

Reputation: 28242

<null> is what NSNull returns for its -description method. You need to also check for

myString == [NSNull null]

in this case.

Additional info: IIRC the common Objective-C JSON stuff will use [NSNull null] for nulls in the JSON structure, to differentiate the value from one that simply isn't there.

Upvotes: 7

Black Frog
Black Frog

Reputation: 11725

NSString * is just a pointer to a NSString object.
To test for null pointer:

NSString *str;

if (str) {
    // str points to an object
    if ([str length] == 0) {
        // string is empty
    }
} else
    // str points to nothing
}

If you want to check for whitespace, you can trim the NSString with stringByTrimmingCharactersInSet.

Upvotes: 2

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