无法在 iPhone 游戏中播放 mp3 文件

Question

我想在我的游戏中播放背景音乐（理想情况下我希望它淡入/淡出，但我希望它先播放）

我查看了关于 SO 的各种答案，我的代码看起来似乎正确，但由于某种原因文件没有播放，实际上它在 AVAudioPlayer *player 行上崩溃（没有有用的输出）。如果我继续，它会在[player play] 行再次崩溃，但error 是0。

再次更新...

GameViewController.h

@property (nonatomic, retain) AVAudioPlayer *player;

GameViewController.m

@synthesize player; // the player object

ViewDidLoad：

NSString *soundFilePath = [[NSBundle mainBundle] pathForResource: @"bgtrack" ofType: @"mp3"];
NSURL *fileURL = [[NSURL alloc] initFileURLWithPath: soundFilePath];

player = [[AVAudioPlayer alloc] initWithContentsOfURL:fileURL error: nil]; // breaks here
[player prepareToPlay];

我包括

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

更新：

根据 cmets，我尝试直接从 Apple 开发中心复制/粘贴代码。我正在使用最新的 XCode 4 和 iOS 6.1 模拟器。

当它崩溃时，我没有得到任何信息栏表明它遇到了断点。该文件包含在包中

Answer 1

您需要存储对 player 的强引用（可能在您的视图控制器的 ivar 或其他东西中）。如果您只是将该代码放入-viewDidLoad 方法或其他东西中而没有对其进行强引用，则会发生的情况是播放器将在有机会开始播放之前被释放。例如：

@interface MyViewController : UIViewController

@end

@implementation MyViewController
{
    AVAudioPlayer* player;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSString *soundFilePath = [[NSBundle mainBundle] pathForResource:@"YourMP3FileName" ofType:@"mp3"];
    NSURL *soundFileURL = [NSURL fileURLWithPath:soundFilePath];
    NSError *error;
    player = [[AVAudioPlayer alloc] initWithContentsOfURL:soundFileURL error:&error];
    player.numberOfLoops = -1; //infinite
    player.currentTime = 139;// 2:19;

    [player play];
}

@end

这对我来说很好，但如果 player 不是视图控制器的 ivar，我就听不到声音。

另外，我创建了以下类，它将作为“一次性”AVAudioPlayer 工作。对于numberOfLoops 为-1（无限）的情况，这显然会出现问题，因为这意味着它永远不会停止播放或消失，但在您想要播放一次然后消失的情况下，它可能会使事情变得稍微容易一些无需保留对它的引用。

OneShotAVAudioPlayer.h

#import <AVFoundation/AVFoundation.h>

@interface OneShotAVAudioPlayer : AVAudioPlayer
@end

OneShotAVAudioPlayer.m

#import "OneShotAVAudioPlayer.h"
#import <AVFoundation/AVFoundation.h>
#import <objc/runtime.h>

@interface OneShotAVAudioPlayer () <AVAudioPlayerDelegate>
@property(weak) id<AVAudioPlayerDelegate> p_exogenousDelegate;
@end

@implementation OneShotAVAudioPlayer

static void * const OneShotAVAudioPlayerKey = (void*)&OneShotAVAudioPlayerKey;

- (id)initWithContentsOfURL:(NSURL *)url error:(NSError **)outError
{
    if (self = [super initWithContentsOfURL:url error:outError])
    {
        // Retain ourself
        objc_setAssociatedObject(self, OneShotAVAudioPlayerKey, self, OBJC_ASSOCIATION_RETAIN);
        [super setDelegate: self];
    }
    return self;
}

- (id)initWithData:(NSData *)data error:(NSError **)outError;
{
    if (self = [super initWithData:data error:outError])
    {
                    // Retain ourself
        objc_setAssociatedObject(self, OneShotAVAudioPlayerKey, self, OBJC_ASSOCIATION_RETAIN);
        [super setDelegate: self];
    }
    return self;
}

- (void)setDelegate:(id<AVAudioPlayerDelegate>)delegate
{
    self.p_exogenousDelegate = delegate;
}

- (id<AVAudioPlayerDelegate>)delegate
{
    return self.p_exogenousDelegate;
}

- (void)audioPlayerDidFinishPlaying:(AVAudioPlayer *)player successfully:(BOOL)flag
{
    @try
    {
        if ([self.p_exogenousDelegate respondsToSelector: _cmd])
            [self.p_exogenousDelegate audioPlayerDidFinishPlaying:player successfully:flag];
    }
    @finally
    {
        // Make a strong ref so we stay alive through the scope of this function
        typeof(self) keepAlive = self;
        // Give up the self retain
        objc_setAssociatedObject(keepAlive, OneShotAVAudioPlayerKey, nil, OBJC_ASSOCIATION_RETAIN);
        // Push in the "real" (outside) delegate, cause our job is done here.
        [super setDelegate: self.p_exogenousDelegate];
    }
}

- (void)audioPlayerDecodeErrorDidOccur:(AVAudioPlayer *)player error:(NSError *)error
{
    @try
    {
        if ([self.p_exogenousDelegate respondsToSelector: _cmd])
            [self.p_exogenousDelegate audioPlayerDecodeErrorDidOccur:player error:error];
    }
    @finally
    {
        // Make a strong ref so we stay alive through the scope of this function
        typeof(self) keepAlive = self;
        // Give up the self retain
        objc_setAssociatedObject(keepAlive, OneShotAVAudioPlayerKey, nil, OBJC_ASSOCIATION_RETAIN);
        // Push in the "real" (outside) delegate, cause our job is done here.
        [super setDelegate: self.p_exogenousDelegate];
    }
}

- (BOOL)respondsToSelector:(SEL)aSelector
{
    BOOL retVal = [super respondsToSelector: aSelector];
    if (!retVal)
    {
        struct objc_method_description method = protocol_getMethodDescription(@protocol(AVAudioPlayerDelegate), aSelector, YES, YES);
        if (method.name)
        {
            retVal = [self.p_exogenousDelegate respondsToSelector: aSelector];
        }
    }
    return retVal;
}

- (id)forwardingTargetForSelector:(SEL)aSelector
{
    id retVal = [super forwardingTargetForSelector:aSelector];
    if (!retVal)
    {
        struct objc_method_description method = protocol_getMethodDescription(@protocol(AVAudioPlayerDelegate), aSelector, YES, YES);
        if (method.name && [self.p_exogenousDelegate respondsToSelector: aSelector])
        {
            retVal = self.p_exogenousDelegate;
        }
    }
    return retVal;
}

- (void)setNumberOfLoops:(NSInteger)numberOfLoops
{
    if (numberOfLoops < 0)
    {
        NSLog(@"Warning! You have set an infinite loop count for an instance of %@ (%p). This means the instance will effectively be leaked.", NSStringFromClass([self class]), self);
    }
    [super setNumberOfLoops: numberOfLoops];
}

@end

发帖here as a gist。

Answer 2

将玩家 ivar 提升为强属性，如果玩家为零，则记录 [error description]。

如果它崩溃了，那肯定是错误的。是否添加了异常断点？