Question

How do I write a program for iPhone (Objective C++) that runs on OS 2.0 but takes advantage of 3.0 features if they’re available?

Example: copy&paste (class UIPasteboard). Nice feature to have, but I don’t want to kill backward compatibility. Do I compile against SDK v. 3 or v. 2? If the latter, how do I create an instance of UIPasteboard, considering it’s not declared in the headers? If the former, won’t some C-linkage functions cause “unresolved reference” upon loading under OS 2.0?

Answer 1

Edit your Target’s build settings like this:

• Set the Base SDK to the version whose APIs you want to use (e.g. 3.0 or 3.1).
• Set the Deployment Target to the lowest OS version you want to support (e.g. 2.2.1).

When building, you compile against the Base SDK. For all symbols that defined in your Base SDK but not available in your Deployment Target, you need to add runtime checks to your code to check for their availability. Examples:

1. Check if UIPasteboard is available:

   Class PasteboardClass = NSClassFromString(@"UIPasteboard");
   if (PasteboardClass != nil) {
       // UIPasteboard is available
   }
   

2. Check if a specific method is available:

   if ([UITableViewCell respondsToSelector:@selector(initWithStyle:reuseIdentifier:)]) {
       // ...
   }