How to check for null value in NSNumber

Question

First off I confess my ignorance, I\'ve learned everything I know about Objective-C in the few months I\'ve been working on my project. I also find it utterly frustrating ho

Answer 1

In some cases, such as missing keys in NSUserDefaults, you get back the literal @"" as an empty string.

Here's my safe check for an NSNumber.

Note the check for it being an NSNumber occurs first because NSNumber doesn't understand isEqualToString

        id savedPin = [[NSUserDefaults standardUserDefaults] valueForKey:@"blah"];  // don't assume is created so don't type as NSNumber*
        if ( ![savedPin isKindOfClass:[NSNumber class]] && [savedPin isEqualToString:@""]) {  

Answer 2

Use [shoObject class] to get the class of an object; so, to test shoObject's class, you would use

[shoObject isKindOfClass:[NSString class]];

Once you've sorted out what markers define an empty string or NSNumber, you can create a macro. I do with this by keeping an IsEmpty macro in a file called CommonMacros.h. Here's the code:

//Thanks Wil
//http://wilshipley.com/blog/2005/10/pimp-my-code-interlude-free-code.html

static inline BOOL IsEmpty(id thing) {
    return thing == nil
    || ([thing isEqual:[NSNull null]]) //JS addition for coredata
    || ([thing respondsToSelector:@selector(length)]
        && [(NSData *)thing length] == 0)
    || ([thing respondsToSelector:@selector(count)]
        && [(NSArray *)thing count] == 0);
}

Then, after importing CommonMacros.h, you can call the function like this:

if (IsEmpty(shotIndex)) {
    //do stuff
}

This should take care of this problem, and will also work on strings, arrays, etc, as you can see from the code. Thanks to Wil Shipley!

Answer 3

In Objective-c, it's nil not null. So:

if (shotIndex != nil) {
   // its not nil
}