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

Question

注意:请参阅底部的更新。

---

我有一个应用程序可以从列表中一个一个地播放视频。因此，为了测试此功能，我创建了一个只有一个 View Controller 的简单应用程序。我在实现 this 之前引用了此博客 View Controller 。 View Controller 命名为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中只注册了一次(在viewDidLoad调用的initPlayer中)。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。 (事实上，在出现问题的原始项目中，nextVideo会预先从服务器缓存一个视频，如果缓存中存在，则返回缓存视频的路径。否则，它返回 nil。)。在这里，首先播放 sintel_trailer.mp4。播放结束后，它播放的不是 elephants_dream_trailer.mp4，而是 big_buck_bunny_trailer.mp4。也就是说，它循环播放中间跳过的视频。那么，是什么导致 MPMoviePlayerPlaybackDidFinishNotification 调用两次？我为此工作了两天，仍然没有运气。有什么想法吗？

更新 1:

目前我正在回调 moviePlayBackDidFinish: 中使用一个开关，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，并希望将其删除。

更新 2:

到目前为止，我一直在使用 iPhone 4.3 模拟器进行尝试。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，它没有任何问题。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)变得毫无用处(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。你知道如何解决这个问题吗？为什么在 4.3 上有两个回调？

更新 3:

我查明了导致问题的线路。它在 playNextVideo 方法中。导致问题的行是 _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，我现在在 moviePlayBackDidFinish:

上使用类似于 UPDATE 1 中的时间技巧，如下所示

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

Answer 1

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只调用一次；

在播放下一个视频之前(在playNextVideo)你必须调用

[_moviePlayer prepareToPlay];

这对我来说很好用!