How to check if a class or CFType is available in Objective-C

Question

I am working in iOS8 right now and I wanted to check if the CFType 'SecAccessControlRef' is available. Since the app will support iOS 7, without a check, the app will crash. For a regular NSClass I would just use a check like

if (NSClassFromString('SomeClass') == NULL)

but is there something similar for non NSClass items?

Answer 1

Rather than testing for the type itself you can test for one of the functions that support the type. When a framework is weak-linked the address of C functions will be NULL if the framework is not present. For example you should be able to use something like:

BOOL isSecAccessControlRefAvailable = SecAccessControlCreateWithFlags != NULL;

See Using Weakly Linked Methods, Functions, and Symbols in Apple's SDK Compatibility Guide.