MPMoviePlayerViewController backgrounding deal. How to continue playing after returning from background to foreground?

Question

I'm working on application for video streaming. It is built with ARC for iOS5. To display view I use MPMoviePlayerViewController this way:

.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];
}

Few words about presented code: when url for video is resolved I create the MPMoviePlayerViewController object for video playback. Playback is started. Then when app is going background with home button MPMoviePlayerViewController automatically pauses playback and dissapears from screen (weird behavior, as for me). Thats why I have to save playback time when app is going background and show existing MPMoviePlayerViewController again with restored playback time when app is back to foreground. It works fine when user presses home button and then is going back to application.

But it doesn't work when user locks the device. WillEnterBackground notification is fired when applicationWillEnterForeground is called, so for locking event it is called too. But in case when user locks the device MPMoviePlayerViewController wasn't being dismissed properly as in situation when user presses home button. It is hidden from the screen, but calling the code

[self presentModalViewController:player animated:YES];

throws the exception

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

I tried to change the code to dismiss 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];
        }
        }
    }

Now it doesn't throw the exception, but displays warning

wait_fences: failed to receive reply: 10004003

Also completion block is never called.

How to properly to solve the background/foreground continue playing with modally displayed MPMoviePlayerViewController? Thanks for replies.

Answer 1

I solved the problem.

Method -willEnterBackground should look like:

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

We have to dismiss MPMoviePlayerViewController manually when app is entering background mode. Pay attention to use only

[self dismissModalViewControllerAnimated:NO];

instead of

[self dismissMoviePlayerViewControllerAnimated];

Thats because MPMoviePlayerViewController was shown with

[self presentModalViewController:player animated:YES];