Mojomonkey Coding

Starting to play with the Address Book on iPhone. One interesting caveat about the Address Book API is it written in C and makes use of Core Foundation (rather than Foundation).

Foundation vs. Core Foundation

Core Foundation provides the basis for Foundation. In fact, Core Foundation provides the basis for all Objective-C types under the hood. From the Apple Documentation we have the following table that defines all types that are shared:

Because these types are actually the same, you can convert back and forth.

Toll Free Bridging

So, back to Address Book. It is written in C using Core Foundation (meaning it returns C types). This means that your Objective-C iPhone code is going to have a mismash of C types when using some of the System level APIs (almost all System level APIs are written in C to reduce memory footprint).

You lose some of the features of Objective-C (you are really just working with C at this point). So, you need to make sure you check for NULL before using a returned type or you will crash. No message passing to “nil” here.

CFStringRef string = StringReturnedHere();
if(string != NULL) {
   PlayWithString(string);
}

However, not all is lost here, and you don’t have to go back to the scary C world if you don’t want to. You can, in fact, convert all these types into Object-C Foundation classes and operate them as you would if it was returned by an Objective-C API.

NSString string = (NSString *)StringReturnedHere();
[string doSomethingCool];

Toll Free Bridging allows you to type cast from one Core Foundation type to a Foundation type and vice versa. This allows you to work with Core Foundation APIs directly but treat the results as Foundation.