NSMutableAttributedString on iOS 3.1.3

Question

I'm dealing with a very odd situation. I'm implementing Attributed Strings into my iOS application, and I had the warning going in that they are available iOS 3.2 and above. Because I still support 3.1.3 on iPhones, I knew I had to weakly link CoreText and probably so some compile time OS check before using them.

I weakly linked the framework, but out of curiosity I just used the class as is and ran it on a 3.1.3 device... and it works. What am I missing here, I'm so confused why this isn't crashing. I'm 100% sure this is a 3.1.3 device, but is NSMutableAttributedString a hidden class on 3.1.3, and thus actually does work because of the dynamic nature of objective-c ?

Answer 1

Did it really work, instead of just not crashing?

Depending on the setting, a non-existent class becomes just nil. Note that in Objective-C you can send a message to a nil. Then it just returns nil or 0. Then [[NSAttibutedString alloc] init] might just return nil, without crashing.

Answer 2

I am the author of the OHAttributedLabel class. Thanks for using it!

The behavior you have is strange, as OHAttributedLabel uses the CoreText framework to draw the NSAttributedStrings on screen.

As CoreText is only available since iOS 3.2, I can't see how it would be possible for this to work under iOS 3.2, especially iOS 3.1.3…?

Answer 3

CoreText was introduced with iOS 3.2. If you weak link against it the app will start, but it will crash on the first instance on calling a CoreText function.

To still be compatible with earlier versions you CAN weak link and avoid CT code by drawing the text with Quartz instead. You would detect if CT exists on the device and use it if yes, otherwise you would have a crude fallback mechanism for your drawing.