How to check that float property of managed object is nil?

Score is NSManagedObject. score.latit开发者_JAVA百科ude is an NSNumber, which actually is a float value.

NSLog(@"%f", [score.latitude floatValue]);

shows 0.000000.

Construction I use to check for nil:

if (score.latitude == nil)

doesn't work.

It's irrelevant that there is a floating-point value stored in your NSNumber instance; the object itself is either nil or not. To check for an object being nil, if( obj == nil ) is functionally equivalent to if( obj ).

So your conditional may not be doing what you expect, but it is checking for nil. You'd need to add more details about what's happening in the body of the if, should you need more specific explanation.

The key point is that sending a message to nil, such as [nil floatValue] always returns 0, interpreted as whatever the return type of the method is. For example, if you send floatValue to nil, you'll get back floating-point 0. If you send a message that should return an object, you'll get nil; a message that should return an int, you get integer 0.

Also be aware that when you say if( score.latitude ), the expression will evaluate false if either score or latitude is nil (because if score is nil, sending latitude to it will return nil.)

A float can be nil, as it isn't an object.

And a NSNumber is not an float value, but has a method, that returns a float value.

use if (score) to check, if the NSNumber got instantiated before.

As I finally understand, the problem is because of Core Data save data to sql database, which stores nil properties as 0.000...