Detect iOS systemVersion and Retina Display

gistfile1.m

+ (NSString*) resolveImageResource:(NSString*)resource
{
    NSString* systemVersion = [[UIDevice currentDevice] systemVersion];
    BOOL isLessThaniOS4 = ([systemVersion compare:@"4.0" options:NSNumericSearch] == NSOrderedAscending);

    // the iPad image (nor retina) differentiation code was not in 3.x, and we have to explicitly set the path
    if (isLessThaniOS4)
    {
        return [NSString stringWithFormat:@"%@.png", resource];
    }
    else {
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)] == YES && [[UIScreen mainScreen] scale] == 2.00) {

        return [NSString stringWithFormat:@"%@-72@2x.png", resource];

    }

    }


    return resource;
}