设置 contentURL 时在 iPhone 4.3 模拟器中再次调用 MPMoviePlayerPlaybackDidFinishNotification答案

【问题标题】：MPMoviePlayerPlaybackDidFinishNotification being called again in iPhone 4.3 simulator when setting contentURL设置 contentURL 时在 iPhone 4.3 模拟器中再次调用 MPMoviePlayerPlaybackDidFinishNotification
【发布时间】：2012-07-02 14:45:53
【问题描述】：

注意：查看底部的更新。

我有一个应用程序可以从列表中逐一播放视频。所以，为了测试这个功能，我创建了一个只有一个视图控制器的简单应用程序。在实现this 视图控制器之前，我参考了这个博客。视图控制器名为TNViewController，其实现如下：

#import <UIKit/UIKit.h>
#import <MediaPlayer/MediaPlayer.h>

@interface TNViewController : UIViewController {
  @private
    NSMutableArray *_videoArray;
    int _currentVideo;

    MPMoviePlayerController *_moviePlayer;
    NSURL *_movieUrl;
}

@end

它的实现是：

#import "TNViewController.h"

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

    [[UIApplication sharedApplication] setStatusBarHidden:YES animated:NO];
    [self.view setFrame:CGRectMake(0, 0, 480, 320)];

    [self initVideos];
    [self initPlayer];
}

- (void) initVideos {
    _videoArray = [[NSMutableArray alloc] init];

    NSString *path = [[NSBundle mainBundle] pathForResource:@"sintel_trailer" ofType:@"mp4" inDirectory:nil];
    [_videoArray addObject:path];
    path = [[NSBundle mainBundle] pathForResource:@"elephants_dream_trailer" ofType:@"mp4" inDirectory:nil];
    [_videoArray addObject:path];
    path = [[NSBundle mainBundle] pathForResource:@"big_buck_bunny_trailer" ofType:@"mp4" inDirectory:nil];
    [_videoArray addObject:path];

    _currentVideo = -1;
}

- (NSString*) nextVideo {
    _currentVideo++;
    if (_currentVideo >= _videoArray.count) {
        _currentVideo = 0;
    }
    return [_videoArray objectAtIndex:_currentVideo];
}

- (void) initPlayer {
    _moviePlayer = [[MPMoviePlayerController alloc]init];

    [self readyPlayer];
    [self.view addSubview:_moviePlayer.view];

    // Register to receive a notification when the movie has finished playing. 
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(moviePlayBackDidFinish:) 
                                                 name:MPMoviePlayerPlaybackDidFinishNotification 
                                               object:_moviePlayer];
}

- (void) readyPlayer {
    _movieUrl    = [NSURL fileURLWithPath:[self nextVideo]];
    [_movieUrl retain];

    _moviePlayer.contentURL = _movieUrl;

    // For 3.2 devices and above
    if ([_moviePlayer respondsToSelector:@selector(loadState)]) {
        // Set movie player layout
        [_moviePlayer setControlStyle:MPMovieControlStyleNone];
        [_moviePlayer setFullscreen:YES];

        // May help to reduce latency
        [_moviePlayer prepareToPlay];

        // Register that the load state changed (movie is ready)
        [[NSNotificationCenter defaultCenter] addObserver:self 
                                                 selector:@selector(moviePlayerLoadStateChanged:) 
                                                     name:MPMoviePlayerLoadStateDidChangeNotification 
                                                   object:nil];
    } else {
        // Register to receive a notification when the movie is in memory and ready to play.
        [[NSNotificationCenter defaultCenter] addObserver:self 
                                                 selector:@selector(moviePreloadDidFinish:) 
                                                     name:MPMoviePlayerContentPreloadDidFinishNotification 
                                                   object:nil];
    }
}

/*---------------------------------------------------------------------------
 * For 3.1.x devices
 *--------------------------------------------------------------------------*/
- (void) moviePreloadDidFinish:(NSNotification*)notification {
    // Remove observer
    [[NSNotificationCenter  defaultCenter]  removeObserver:self 
                                                      name:MPMoviePlayerContentPreloadDidFinishNotification 
                                                    object:nil];

    // Play the movie
    [_moviePlayer play];
}

/*---------------------------------------------------------------------------
 * For 3.2 and 4.x devices
 *--------------------------------------------------------------------------*/
- (void) moviePlayerLoadStateChanged:(NSNotification*)notification {
    NSLog(@"moviePlayerLoadStateChanged");
    // Unless state is unknown, start playback
    if ([_moviePlayer loadState] != MPMovieLoadStateUnknown) {
        // Remove observer
        [[NSNotificationCenter defaultCenter]  removeObserver:self
                                                         name:MPMoviePlayerLoadStateDidChangeNotification 
                                                       object:nil];

        // Set frame of movie player
        [[_moviePlayer view] setFrame:CGRectMake(0, 0, 480, 320)];
        // Play the movie
        [_moviePlayer play];
    }
}

- (void) moviePlayBackDidFinish:(NSNotification*)notification {    
    NSLog(@"playback finished...");
    NSLog(@"End Playback Time: %f", _moviePlayer.endPlaybackTime);
    int reason = [[[notification userInfo] valueForKey:MPMoviePlayerPlaybackDidFinishReasonUserInfoKey] intValue];
    if (reason == MPMovieFinishReasonPlaybackEnded) {
        NSLog(@"Reason: movie finished playing");
    }else if (reason == MPMovieFinishReasonUserExited) {
        NSLog(@"Reason: user hit done button");
    }else if (reason == MPMovieFinishReasonPlaybackError) {
        NSLog(@"Reason: error");
    }

    [self playNextVideo];
}

- (void) playNextVideo {
    NSString *filePath = [self nextVideo];

    [_movieUrl release];
    _movieUrl = [NSURL fileURLWithPath:filePath];    
    [_movieUrl retain];

    _moviePlayer.contentURL = _movieUrl;
    [_moviePlayer play];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
    return (interfaceOrientation == UIInterfaceOrientationLandscapeRight);
}

- (void) dealloc {
    [_moviePlayer release];
    [_movieUrl release];
    [_videoArray release];

    [super dealloc];
}

@end

现在，我的问题是通知MPMoviePlayerPlaybackDidFinishNotification 被调用了两次。从上面的代码可以看出，我在viewDidLoad（在initPlayer 中从viewDidLoad 调用）中只注册了一次。这是日志输出：

2012-07-02 12:29:17.661 DemoApp[1191:ef03] moviePlayerLoadStateChanged
2012-07-02 12:30:11.470 DemoApp[1191:ef03] playback finished...
2012-07-02 12:30:11.471 DemoApp[1191:ef03] End Playback Time: -1.000000
2012-07-02 12:30:11.472 DemoApp[1191:ef03] Reason: movie finished playing
2012-07-02 12:30:11.474 DemoApp[1191:ef03] playback finished...
2012-07-02 12:30:11.475 DemoApp[1191:ef03] End Playback Time: -1.000000
2012-07-02 12:30:11.476 DemoApp[1191:ef03] Reason: movie finished playing

2012-07-02 12:31:03.821 DemoApp[1191:ef03] playback finished...
2012-07-02 12:31:03.822 DemoApp[1191:ef03] End Playback Time: -1.000000
2012-07-02 12:31:03.824 DemoApp[1191:ef03] Reason: movie finished playing
2012-07-02 12:31:03.826 DemoApp[1191:ef03] playback finished...
2012-07-02 12:31:03.827 DemoApp[1191:ef03] End Playback Time: -1.000000
2012-07-02 12:31:03.827 DemoApp[1191:ef03] Reason: movie finished playing

如您所见，播放完成被调用了两次。这会导致从队列中跳过一个视频。（其实在原项目中出现问题，nextVideo提前从服务器缓存了一个视频，如果缓存中存在则返回缓存视频的路径，否则返回nil .）。在这里，首先播放sintel_trailer.mp4。完成播放后，它会播放big_buck_bunny_trailer.mp4，而不是elephants_dream_trailer.mp4。也就是说，它会循环播放在其间跳过的视频。那么，是什么导致MPMoviePlayerPlaybackDidFinishNotification 调用两次？我正在为此工作两天，仍然没有运气。有什么想法吗？

更新 1：

目前我在回调moviePlayBackDidFinish: 中使用了一个开关，如下所示，并且正在工作：

if (!_playNextVideo) {
    _playNextVideo = YES;
    return;
}
_playNextVideo = NO;
// code to play video....

但我仍然想知道是什么导致回调被调用两次。我觉得当前的 switch 解决方案就像一个 hack，并且喜欢将其删除。

更新 2：

直到现在，我一直在用 iPhone 4.3 模拟器尝试这个。但是，当我用 iPhone 5.0 模拟器和 iPhone 5.1 模拟器尝试相同的程序时，它可以正常工作。也就是说，电影播放完毕后只发送一个回调。这使我的小技巧（更新 1）变得无用（它解决了 4.3 中的问题，但在 5.0 和 5.1 中产生了问题）。我正在使用在 MacOSX Lion - 10.7.4 上运行的 Xcode 4.3.2。您对如何解决此问题有任何想法吗？为什么在 4.3 上有两个回调？

更新 3：

我查明线路导致问题。它在playNextVideo 方法中。导致问题的线路是_moviePlayer.contentURL = _movieUrl;。在第一个回调中更改它会导致再次发送 MPMoviePlayerPlaybackDidFinishNotification。但是，它只发生在 iPhone 4.3 模拟器中。有什么想法吗？

更新 4：

不过，我对这种奇怪的行为一无所知。所以，我现在正在使用类似于 UPDATE 1 中的时间技巧，如下moviePlayBackDidFinish:

NSTimeInterval currentCallback = [NSDate timeIntervalSinceReferenceDate];
NSTimeInterval difference      = currentCallback - _lastCallback;
_lastCallback                  = currentCallback;
if (difference < 5.0) {
    return;
}
// code to play video....

【问题讨论】：

我使用 AVQueuePlayer 解决了一个类似的问题，使用 AVAsset 和 AVPlayerItem 以更少的代码处理非常好的排队电影。
@Winston 目前，我正在使用时间技巧（请参阅更新的问题）。我确实看过AVQueuePlayer、AVAsset 和AVPlayerItem，在这种情况下它似乎是一个不错的候选者。感谢您指出它们（我以前没有听说过它们）。不幸的是，那个项目已经结束了，我现在在做一个不同的项目。但是，从现在开始，我会强烈考虑在新项目中使用AVQueuePlayer。
很高兴能向您指出一些新的东西，感谢您的回复。

标签： iphone objective-c ios mpmediaplayercontroller

【解决方案1】：

您可以为下一首曲目创建新播放器：

MPMoviePlayerController *player = [[MPMoviePlayerController alloc] initWithContentURL: _movieUrl];
if (player)
{
    [self setMoviePlayer:player];
}
[self.moviePlayer play];

代替

self.moviePlayer.contentURL = _movieUrl;

通知MPMoviePlayerPlaybackDidFinishNotification 将调用一次。

【讨论】：

【解决方案2】：

我遇到了同样的问题。并以这种方式解决：

我创建了一种跳过视频的新方法

- (void) skipVideo {
    [_moviePlayer stop];
}

在skipVideo 中停止播放器将导致MPMovieFinishReasonPlaybackEnded 通知（在模拟器和设备上）。现在设置播放器的contentUrl时，不会引起其他MPMovieFinishReasonPlaybackEnded通知，所以moviePlayBackDidFinish只被调用一次；

在播放下一个视频（playNextVideo）之前，您必须致电

[_moviePlayer prepareToPlay];

这对我来说很好！

【讨论】：