dyld: Symbol not found: _AVSpeechUtteranceMaximumSpeechRate - ios6

Question

I'm trying to use my code to be compatible for both iOS 6 & 7, using the synthesized speech.
I wanna it to be available for iOS 7 and not available for iOS 6.
The problem is when I run in the simulator in iOS 6 it gives following error even before the simulator get to start: dyld: Symbol not found: _AVSpeechUtteranceMaximumSpeechRate
.
If I comment the line: utterance.rate = AVSpeechUtteranceMaximumSpeechRate / 4.0f; works great for iOS 6 to start even if its not designed for it.
What be the issue?
Thanks.
if (floor(NSFoundationVersionNumber) > NSFoundationVersionNumber_iOS_6_1) {
// Load resources for iOS 7 or later
AVSpeechSynthesizer *synthesizer = [[AVSpeechSynthesizer alloc] init];
AVSpeechUtterance *utterance = [AVSpeechUtterance speechUtteranceWithString:selectedText];
utterance.rate = AVSpeechUtteranceMaximumSpeechRate / 4.0f;
utterance.voice = [AVSpeechSynthesisVoice voiceWithLanguage:#"en-US"]; // defaults to your system language
[synthesizer speakUtterance:utterance];
[synthesizer release];
}
else{
// Load resources for iOS 6 or earlier
UIAlertView *alert = [[[UIAlertView alloc] initWithTitle:#"Sorry"
message:#"This feature requires iOS 7.0 or later"
delegate:Nil
cancelButtonTitle:#"OK"
otherButtonTitles: nil] autorelease];
[alert show];
}

Answer 1

Just add this line at the top of your file:
AVF_EXPORT const float AVSpeechUtteranceMaximumSpeechRate NS_AVAILABLE_IOS(7_0);
With a weakly imported symbol, dyld will not crash if it doesn’t find the symbol when your app starts.