Learning the iOS 4 SDK for JavaScript Programmers

Boolean Values

The single binary digit representing values 1 and 0 has had a long history of also representing the two states of a Boolean value. For the sake of code readability, many languages equate the constants true and false to those numeric values, respectively. That’s how JavaScript does it, and so does current C language practice.

But in the Objective-C world of the iOS SDK, you will more commonly use the constants YES and NO to represent Boolean values. In Chapter 5 you saw how a Boolean value was passed as an argument to the method that displayed a second view. In that case, the method required a Boolean value to signify whether the transition should be animated:

    [self presentModalViewController:secondViewController animated:YES];

If you define a method that returns a Boolean value, the return type is specified as (BOOL). You can extract the BOOL value from an NSString or NSNumber object via the boolValue method of those classes. Although you can get away with continuing to use true and false or 1 and 0, it’s a good idea to make your code as Objective-C-compliant as possible. Finally, if you wish to view a Boolean value in a format string (as in NSLog()), use the %d format specifier, which will display the integers 1 or 0, or create a conditional operator statement that returns more readable words, as in the following:

NSLog(@"flagValue = %@", (flagValue ? @"YES" : @"NO"));