objective-c - MPMoviePlayerViewController 后台处理。从后台返回前台后如何继续播放？

Question

我正在处理视频流应用程序。它是用 ARC for iOS5 构建的。 为了显示 View ，我以这种方式使用 MPMoviePlayerViewController:

.h

@interface EpisodesTableViewController : UITableViewController<EpisodeUrlResolverDelegate> {
    NSTimeInterval playbackTime;
    EpisodeUrlResolver *episodeUrlResolver;
}
@property (strong, nonatomic) MPMoviePlayerViewController *player;
@end

.m

@implementation EpisodesTableViewController
@synthesize episodes, player;

- (void)viewDidLoad
{
    [super viewDidLoad];
    episodeUrlResolver = [[Soap4MeEpisodeUrlResolver alloc] init];
    [episodeUrlResolver setDelegate:self];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willEnterForeground) name:@"WillEnterForeground" object:nil];                 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(willEnterBackground) name:@"WillEnterBackground" object:nil];
}

- (void)viewDidUnload
{
    episodeUrlResolver = nil;
    player = nil;
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"WillEnterForeground" object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:@"WillEnterBackground" object:nil];
    [super viewDidUnload];
}

- (void)url:(NSURL *)url WasResolvedForEpisode:(Episode *)episode {
    player = [[MPMoviePlayerViewController alloc] initWithContentURL:url];
    player.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
    player.moviePlayer.allowsAirPlay = YES;
    [self presentModalViewController:player animated:YES];
}

- (void)willEnterBackground {
    if (player) {
        playbackTime = player.moviePlayer.currentPlaybackTime;
    }
}

- (void)willEnterForeground {
    if (!player)
        return;
    if(player.moviePlayer.playbackState == MPMoviePlaybackStateInterrupted || player.moviePlayer.playbackState == MPMoviePlaybackStateStopped || player.moviePlayer.playbackState == MPMoviePlaybackStatePaused)
    {
        [self continuePlayback];
    }
}

- (void)continuePlayback {
    [self presentModalViewController:player animated:YES];
    [player.moviePlayer setInitialPlaybackTime:playbackTime];
    NSLog(@"%f", player.moviePlayer.initialPlaybackTime);
    [player.moviePlayer play];
}

关于提供的代码的几句话: 当视频的 url 被解析后，我创建了用于视频播放的 MPMoviePlayerViewController 对象。播放开始。然后当应用程序使用主页按钮进入后台时 MPMoviePlayerViewController 自动暂停播放并从屏幕上消失(奇怪的行为，对我来说)。这就是为什么我必须在应用程序进入后台时节省播放时间，并在应用程序返回前台时再次显示现有的 MPMoviePlayerViewController 并恢复播放时间。 当用户按下主页按钮然后返回应用程序时，它工作正常。

但当用户锁定设备时它不起作用。 WillEnterBackground 通知在 applicationWillEnterForeground 被调用，因此对于锁定事件它也被调用。 但是如果用户锁定设备时 MPMoviePlayerViewController 没有像用户按下主页按钮时那样被正确关闭。它在屏幕上是隐藏的，但是调用代码

[self presentModalViewController:player animated:YES];

抛出异常

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Application tried to present modally an active controller <EpisodesTableViewController: 0x91b3950>.'

我试图更改代码以关闭 Controller :

- (void)willEnterForeground {
        if (!player)
            return;
        if(player.moviePlayer.playbackState == MPMoviePlaybackStateInterrupted || player.moviePlayer.playbackState == MPMoviePlaybackStateStopped || player.moviePlayer.playbackState == MPMoviePlaybackStatePaused)
        {
            if (self.presentedViewController) {
            [self dismissViewControllerAnimated:YES completion:^{
                [self continuePlayback];

            }];
        }
        else {
            [self continuePlayback];
        }
        }
    }

现在它不会抛出异常，但会显示警告

wait_fences: failed to receive reply: 10004003

completion block 也永远不会被调用。

如何正确解决背景/前景继续播放模态显示的 MPMoviePlayerViewController？ 感谢您的回复。

Answer 1

我解决了这个问题。

方法 -willEnterBackground 应该如下所示:

- (void)willEnterBackground {
    if (player) {
        playbackTime = player.moviePlayer.currentPlaybackTime;
        [self dismissModalViewControllerAnimated:NO];
    }
}

当应用进入后台模式时，我们必须手动关闭 MPMoviePlayerViewController。 注意只用

[self dismissModalViewControllerAnimated:NO];

代替

[self dismissMoviePlayerViewControllerAnimated];

那是因为 MPMoviePlayerViewController 显示为

[self presentModalViewController:player animated:YES];