ios: add printing, but keep compatibility with ios 3

i'm trying to add printing features to an ios app. while printing itself works fine, and the app works on ios > 4, i haven't figured out yet how to keep the ios 3.1 compatibility...

i guess the issue is this: completionHandler:(UIPrintInteractionCompletionHandler)

A block of type UIPrintInteractionCompletionHandler that you implement to handle the conclusion of the print job (for instance, to reset state) and to handle any errors encountered in printing.

once i add the block:

void (^completionHandler)(UIPrintInteractionController *, BOOL, NSError *) =
^(UIPrintInteractionController *printController, BOOL completed, NSError *error) {
};

the app won't even launch on iOS 3.1 probably because blocks aren't available there.

yes, i made sure that this code won't be run when launched on iOS 3.1...

if (([[[UIDevice currentDevice] systemVersion] floatValue] >= 4.2) && ([UIPrintInteractionController isPrintingAvailable]))

so i wonder if there's a way to have printing support for iOS >4.2, but keeping it to run on iOS 3.1?

maybe there's a way to use a method instead of the "block"? or how would be the correct way to have printing available on supported iOS devices, and remain backwards compatible to iOS 3.1?

Solution

just add -weak_framework UIKit to the project settings under "Other Linker Flags" and make sure you use conditional code for printing API. Conditional code should check feature availability, not OS version:

    if (NSClassFromString(@"UIPrintInteractionController")){
    void (^completionHandler)(UIPrintInteractionController *, BOOL, NSError *) =
    ^(UIPrintInteractionController *printController, BOOL completed, NSError *error) {
    };
}

Set your project target to iOS 3, and you're good to go.