检测麦克风是否被开启? 没开启的 调用录音功能就提示一次

if ([[AVAudioSession sharedInstance] respondsToSelector:@selector(requestRecordPermission:)]) {
[[AVAudioSession sharedInstance] performSelector:@selector(requestRecordPermission:) withObject:^(BOOL granted) {
if (granted) {
// Microphone enabled code
NSLog(@"Microphone is enabled..");
}
else {
// Microphone disabled code
NSLog(@"Microphone is disabled..");

// We're in a background thread here, so jump to main thread to do UI work.
dispatch_async(dispatch_get_main_queue(), ^{
[[[[UIAlertView alloc] initWithTitle:@"Microphone Access Denied"
message:@"This app requires access to your device's Microphone. Please enable Microphone access for this app in Settings / Privacy / Microphone"
delegate:nil
cancelButtonTitle:@"Dismiss"
otherButtonTitles:nil] autorelease] show];
});
}
}];
}