AVAudioPlayer is always nill and its isPlaying property is always false. The files are mixed while playing

问题

I've been pulling out my hair past three days to fix this problem. I've checked lots of sample codes, read lots of tutorials, and googled and checked lots and lots of questions and answers on stackoverflow, but I still cannot fix the problem. There are several similar questions like this or this but they don't have any solutions either.

So a little bit about my project:

I have a NIKMasterViewController and a NIKDetailViewController. In the first one I have a list of audio files in a table view; selecting a row, it navigates to the NIKDetailViewController where the user can see some info about the file and play the audio file. I've defined an AVAudioPlayer property in the NIKMasterViewController and have set it like this: NIKMasterViewController.h:

@property (nonatomic, strong) AVAudioPlayer *audioPlayer;

NIKMasterViewController.m:

@synthesize audioPlayer;

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([[segue identifier] isEqualToString:@"showDetail"])
    {
        NSIndexPath *indexPath = [self.tableView indexPathForCell:sender];
        NIKDetailViewController *detailViewController = (NIKDetailViewController *) segue.destinationViewController;
        [detailViewController setAudioPlayer:audioPlayer];

        [detailViewController setFeedEntry:[[[self feedParser] feedItems] objectAtIndex:indexPath.row]];

    } else {
        NSLog(@"Segue Identifier: %@", segue.identifier);
    }

}

And that's all about the AVAudioPlayer in NIKMasterViewController. Now in my NIKDetailViewController I have another property of AVAudioPlayer:

NIKDetailViewController.h:

@property (nonatomic, strong) AVAudioPlayer *audioPlayer;

Now in my .m file I have a method called streamAudio which is called in viewDidLoad to prepare the audio playback, and I have an if condition asking to check if the audioPlayer is nill and if not, if the audioPlayer.isPlaying is true so that it stops the player, but it's never called, and when i navigate back to the Master VC to tap on another row to play another file, the second file starts playing while the first file is being played and everything gets mixed up.

Any help will be truly appreciated, since I'm almost about to stop programming after being unable to fix this issue after hours and days!

NIKDetailViewController.m:

@synthesize audioPlayer;


- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
        selectedItem = [[NSString alloc]init];
    }
    return self;
}


#pragma mark - Managing the Audio Playback


- (IBAction)togglePlayingState:(id)button
{
    //Handle the button pressing
    [self togglePlayPause];
}



- (void)playAudio
{
    //Play the audio and set the button to represent the audio is playing
    [audioPlayer play];
    [playPauseButton setImage:[UIImage imageNamed:@"player_pause"] forState:UIControlStateNormal];
}

- (void)pauseAudio
{
    //Pause the audio and set the button to represent the audio is paused
    [audioPlayer pause];
    [playPauseButton setImage:[UIImage imageNamed:@"player_play"] forState:UIControlStateNormal];

}

- (void)togglePlayPause
{
    //Toggle if the music is playing or paused
    if (!audioPlayer.playing)
    {
        [self playAudio];
    }
    else if (audioPlayer.playing)
    {
        [self pauseAudio];
    }
}


- (void)streamAudio
{   
    currentFileName = [[feedEntry podcastDownloadURL] lastPathComponent];

    NSString* documentPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSString* path = [documentPath stringByAppendingPathComponent:currentFileName];
    NSURL* audioURL = [NSURL fileURLWithPath: path];

    if (audioPlayer != nil)
    {
        if (audioPlayer.isPlaying)
        {
            [audioPlayer stop];  //THIS IS NEVER CALLED
        }
        audioPlayer = nil;           //THIS IS NEVER CALLED
    }

    audioPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:audioURL error:nil];

    // Set a timer which keep getting the current music time and update the UISlider in 1 sec interval
    playbackTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateSlider) userInfo:nil repeats:YES];
    // Set the maximum value of the UISlider
    seekSlider.maximumValue = audioPlayer.duration;


    currentTime.text = [NSString stringWithFormat:@"%d:%02d", (int)audioPlayer.currentTime / 60, (int)audioPlayer.currentTime % 60, nil];
    remainingTime.text = [NSString stringWithFormat:@"%d:%02d", (int)(audioPlayer.duration - audioPlayer.currentTime) / 60, (int)(audioPlayer.duration - audioPlayer.currentTime) % 60, nil];

    // Set the valueChanged target
    [seekSlider addTarget:self action:@selector(sliderChanged:) forControlEvents:UIControlEventValueChanged];
    audioPlayer.delegate = self;
    [audioPlayer prepareToPlay]; //Add the audio to the memory.
}


- (void)updateSlider
{
    // Update the slider about the music time
    seekSlider.value = audioPlayer.currentTime;
}

- (IBAction)sliderChanged:(UISlider *)sender {
    // Fast skip the music when user scrolls the slider
    [audioPlayer stop];
    [audioPlayer setCurrentTime:seekSlider.value];
    audioPlayer.delegate = self;

    [audioPlayer prepareToPlay];
    [audioPlayer play];
}

// Stop the timer when the music is finished (Need to implement the AVAudioPlayerDelegate in the Controller header)
- (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag {
    // Music completed
    if (flag) {
        [playbackTimer invalidate];
    }
}


- (IBAction)forwardAudio:(id)sender
{
    int currentTime = [audioPlayer currentTime];
    [audioPlayer setCurrentTime:currentTime+10];
}

- (IBAction)rewindAudio:(id)sender
{
    int currentTime = [audioPlayer currentTime];
    [audioPlayer setCurrentTime:currentTime-10];
}


//Make sure we can recieve remote control events
- (BOOL)canBecomeFirstResponder {
    return YES;
}

- (void)remoteControlReceivedWithEvent:(UIEvent *)event {
    //if it is a remote control event handle it correctly
    if (event.type == UIEventTypeRemoteControl) {
        if (event.subtype == UIEventSubtypeRemoteControlPlay) {
            [self playAudio];
        } else if (event.subtype == UIEventSubtypeRemoteControlPause) {
            [self pauseAudio];
        } else if (event.subtype == UIEventSubtypeRemoteControlTogglePlayPause) {
            [self togglePlayPause];
        }
    }
}

#pragma mark - view life cycle


- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];

    //Once the view has loaded then we can register to begin recieving controls and we can become the first responder
    [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];
    [self becomeFirstResponder];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    //End recieving events
    [[UIApplication sharedApplication] endReceivingRemoteControlEvents];
    [self resignFirstResponder];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    [self streamAudio];

    //Make sure the system follows our playback status - to support the playback when the app enters the background mode.
    [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
    [[AVAudioSession sharedInstance] setActive: YES error: nil];

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
@end

NOTE: I have tried setting the property in the Detail VC as weak but then, I get a warning, and the property is release before I can play the file.

回答1:

So... I could finally fix this problem by creating a singleton of the audioplayer. This is how:

First of all, I removed all the code related to the audioPlayer from my NIKMasterViewController class, that includes the audioPlayer declaration and setting it in prepareForSegue.
I created a new class called NIKAudioPlayer.

In NIKAudioPlayer.h:

#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>

@interface NIKAudioPlayer : NSObject <AVAudioPlayerDelegate>
{
    AVAudioPlayer *currentPlayer;
}
@property (nonatomic, strong) AVAudioPlayer *currentPlayer;
+(NIKAudioPlayer *) sharedPlayer;
-(void)playURL:(NSURL*)url;
@end

In NIKAudioPlayer.m:

#import "NIKAudioPlayer.h"

@implementation NIKAudioPlayer 
@synthesize currentPlayer;

+(NIKAudioPlayer *) sharedPlayer
{
    static NIKAudioPlayer* sharedPlayer;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
    sharedPlayer = [[NIKAudioPlayer alloc] init];
    });
    return sharedPlayer;
}

-(void)playURL:(NSURL*)url
{
    [currentPlayer stop];
    currentPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:url error:nil];
    [currentPlayer prepareToPlay];
}

@end

Now in everywhere else in the code (in my case in NIKDetailViewController) whenever I need to play an audio file, I call the sharedPlayer from NIKAudioPlayer:
```
[[NIKPlayer sharedPlayer] playURL:audioURL];
[[NIKPlayer sharedPlayer].currentPlayer prepareToPlay];
```

To put in a nutshell, replace all audioPlayers in NIKDetailViewController with [NIKPlayer sharedPlayer].currentPlayer, or even cast it and use it everywhere:

audioPlayer = [NIKPlayer sharedPlayer].currentPlayer

来源：https://stackoverflow.com/questions/20164873/avaudioplayer-is-always-nill-and-its-isplaying-property-is-always-false-the-fil

标签

ios

objective-c

avaudioplayer