viewDidLoad 中异步加载声音资源崩溃

Question

所有，

我试图在加载 UIViewController 时异步加载一组声音。大约在同一时间，我（偶尔）还会将 UIView 放置在 ViewController 层次结构的顶部以显示帮助叠加层。当我这样做时，应用程序会因执行错误而崩溃。如果未添加视图，应用程序不会崩溃。我的 ViewController 看起来像这样：

- (void)viewDidLoad
{
    [super viewDidLoad];

    __soundHelper = [[SoundHelper alloc] initWithSounds];

    // Other stuff
}

- (void)viewDidAppear:(BOOL)animated
    {
    // ****** Set up the Help Screen
    self.coachMarkView = [[FHSCoachMarkView alloc] initWithImageName:@"help_GradingVC" 
                                                    coveringView:self.view 
                                                     withOpacity:0.9 
                                                    dismissOnTap:YES 
                                                    withDelegate:self];

    [self.coachMarkView showCoachMarkView];
    [super viewDidAppear:animated];
}

SoundHelper 的主要异步加载方法（从“initWithSounds”调用）看起来像这样：

// Helper method that loads sounds as needed
- (void)loadSounds {

    // Run this loading code in a separate thread
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    NSBlockOperation *loadSoundsOp = [NSBlockOperation blockOperationWithBlock:^{
        // Find all sound files (*.caf) in resource bundles
        __soundCache = [[NSMutableDictionary alloc]initWithCapacity:0];

        NSString * sndFileName;
        NSArray *soundFiles = [[NSBundle mainBundle] pathsForResourcesOfType:STR_SOUND_EXT inDirectory:nil];

        // Loop through all of the sounds found
        for (NSString * soundFileNamePath in soundFiles) {
            // Add the sound file to the dictionary
            sndFileName = [[soundFileNamePath lastPathComponent] lowercaseString];
            [__soundCache setObject:[self soundPath:soundFileNamePath] forKey:sndFileName];
        }

        // From: https://stackoverflow.com/questions/7334647/nsoperationqueue-and-uitableview-release-is-crashing-my-app
        [self performSelectorOnMainThread:@selector(description) withObject:nil waitUntilDone:NO];
    }];
    [operationQueue addOperation:loadSoundsOp];
}

崩溃似乎发生在块退出时。 FHSCoachMarkView 的 init 看起来像这样：

- (FHSCoachMarkView *)initWithImageName:(NSString *) imageName 
                           coveringView:(UIView *) view
                            withOpacity:(CGFloat) opacity
                           dismissOnTap:(BOOL) dismissOnTap
                           withDelegate:(id<FHSCoachMarkViewDelegate>) delegateID
{
    // Reset Viewed Coach Marks if User Setting is set to show them
    [self resetSettings];

    __coveringView = view;        
    self = [super initWithFrame:__coveringView.frame];
    if (self) {
        // Record the string for later reference
        __coachMarkName = [NSString stringWithString:imageName];
        self.delegate = delegateID;

        UIImage * image = [[UIImage alloc] initWithContentsOfFile:[[NSBundle mainBundle] pathForResource:imageName ofType:@"png"]];

        // ****** Configure the View Hierarchy
        UIImageView *imgView = [[UIImageView alloc] initWithImage:image];

        [self addSubview:imgView];
        [__coveringView.superview insertSubview:self aboveSubview:__coveringView];

        // ****** Configure the View Hierarchy with the proper opacity
        __coachMarkViewOpacity = opacity;
        self.hidden = YES;
        self.opaque = NO;
        self.alpha = __coachMarkViewOpacity;

        imgView.hidden = NO;
        imgView.opaque = NO;
        imgView.alpha = __coachMarkViewOpacity;

        // ****** Configure whether the coachMark can be dismissed when it's body is tapped
        __dismissOnTap = dismissOnTap;

        // If it is dismissable, set up a gesture recognizer
        if (__dismissOnTap) {
            UITapGestureRecognizer * tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self 
                                                                                      action:@selector(coachMarkWasTapped:)];
            [self addGestureRecognizer:tapGesture];
        }
    }
    return self;
}

我尝试使用 NSBlockOperation 和 dispatch_async 以及两者来调用异步块也得到了同样的结果。此外，我完全删除了 aysnch 调用并将声音加载到主线程上。效果很好。我还尝试了@Jason建议的解决方案： NSOperationQueue 和 UITableView 版本是使我的应用程序崩溃，但同样的事情也发生在那里。

这实际上是 FHSCoachMarkView 中添加的视图的问题，还是可能与两者访问 mainBundle 的事实有关？我对 iOS 中的异步编码有点陌生，所以我有点不知所措。任何帮助将不胜感激！

谢谢， 斯科特

Answer 1

我发现了这一点：我在 SoundHelper 对象 (NSUserDefaultsDidChangeNotification) 上设置了一个监听器，用于监听 NSUserDefaults 何时更改，并在用户默认指示时加载声音。 FHSCoachMarkView 还对 NSUserDefaults 进行了更改。在 SoundHelper 中，我没有正确检查哪些默认值正在更改，因此每次进行更改时都会调用异步声音加载方法。因此多个线程试图修改 __soundCache 实例变量。它似乎不喜欢那样。

问题：这是回答您自己的问题的正确方法吗？或者我应该只对问题本身添加评论？

谢谢。