How to select and play different audio files with AVAudioPlayer - ios

Question

I am currently using AVAudioPlayer to play an MP3 file when the method is triggered.
This works well however I would now like to add in the ability to select which audio file is played when the method is triggered from a list, this is not going so well.
I have created a UISegmentedControl and attempted to change the AVAudioPlayer method to reflect what has been selected however I am now receiving the following error when the app is launched:
'NSInvalidArgumentException', reason: '*** -[NSURL
initFileURLWithPath:]: nil string parameter'
From what I understand, I am recieving the above error because when the AVAudioPlayer is attempting to initWithContentsOfUrl:, the string being referenced does not contain any data yet, I thought it may have got this from the default segment in the UISegmentedController, however this is not the case.
I have searched for a solution for this but could not find anything which matched what i was attempting to achieve, the closest I could find was to initiate a new session of AVAudioPlayer for every audio file I wanted to play however this seemed very long winded and ultimatly may still not work.
Below is my code so far, if you could suggest how I could make this work, I would appreciate it.
for the UISegmentedController:
- (void) selectTone:(id)sender
{
if (self.alarmToneType == 0) {
self.filePath = [[NSBundle mainBundle] pathForResource: #"alarm" ofType: #"mp3"];
NSLog(#"Tone Selected 0 %#", [HRASettingsViewController alarmToneDescription:(int) self.alarmToneType]);
}
if (self.alarmToneType == 1) {
self.filePath = [[NSBundle mainBundle] pathForResource: #"redalert" ofType: #"mp3"];
NSLog(#"Tone Selected 1 %#", [HRASettingsViewController alarmToneDescription:(int) self.alarmToneType]);
}
if (self.alarmToneType == 2) {
self.filePath = [[NSBundle mainBundle] pathForResource: #"greenalaert" ofType: #"mp3"];
NSLog(#"Tone Selected 2 %#", [HRASettingsViewController alarmToneDescription:(int) self.alarmToneType]);
}
}
I have created the string as a #property above but didn't think you would need that.
for the AVAudioPlayer:
- (void) setupAppAudio {
/////////////////////////////////////////////////////////////////////////////////////
// SOUNDS
// Registers this class as the delegate of the audio session.
[[AVAudioSession sharedInstance] setActive:YES error:nil];
// Use this code instead to allow the app sound to continue to play when the screen is locked.
NSError *sessionError = nil;
[[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayback error: &sessionError];
if (sessionError) {
NSLog(#"AVAudioSession ERROR %#", sessionError);
} else {
NSLog(#"AVAudioSession SUCCESSFUL");
}
// Tell other music to be quiet when we are talking!
UInt32 doSetProperty = 1;
AudioSessionSetProperty (kAudioSessionProperty_OtherMixableAudioShouldDuck,
sizeof (doSetProperty),
&doSetProperty);
// Registers the audio route change listener callback function
AudioSessionAddPropertyListener (kAudioSessionProperty_AudioRouteChange,
audioRouteChangeListenerCallback,
(__bridge void *)(self));
NSError *activationError = nil;
[[AVAudioSession sharedInstance] setActive: YES error: &activationError];
// setup
//NSString *filePath;
AVAudioPlayer *newPlayer;
newPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL: [NSURL fileURLWithPath:self.filePath] error: nil];
self.beepPlayer = newPlayer;
// "Preparing to play" attaches to the audio hardware and ensures that playback
// starts quickly when the user taps Play
[self.beepPlayer prepareToPlay];
[self.beepPlayer setVolume: 1.0];
[self.beepPlayer setDelegate: self];
}