android - 我如何让 ExoPlayer 在我的 Activity 的 onStart() 方法中恢复视频？

Question

我正在使用 ExoPlayer 从 URL 播放一些 mp4。当用户单击主页按钮或任何导致应用程序从用户 View 中删除然后返回到我的应用程序(和视频 Activity )时，我希望视频从它停止的地方继续播放。我尝试通过在 onStop() 中保存视频位置然后重建播放器并在 onStart() 中使用 seekTo() 来实现这一点。我在 onStart() 中检查我当前的 exoplayer 是否为 null，但是此检查从未通过，所以我认为这就是问题所在。现在它是如何编码的我的视频永远不会恢复。如果我通过按下主页按钮离开应用程序 onStop() 被调用，然后当我返回我的应用程序时 onStart() 将被调用，但是视频播放器仍然存在黑色，从不播放视频。如果我删除空检查，每当我从主要 Activity 开始播放视频时，我都会播放两个视频实例，因为它在 onCreate() 和 onStart() 中都被调用.有没有更好的方法来获得我想要的功能？感谢您的帮助!

public class VideoActivity extends AppCompatActivity {

    private SimpleExoPlayer exoPlayer;
    private SimpleExoPlayerView simpleExoPlayerView;
    private long playerPosition;
    private String mp4Url;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.player_activity);

        // Get the Intent that started this activity and extract the video url
        Intent intent = getIntent();
        mp4Url = intent.getStringExtra(MainActivity.VIDEO_URL);
        // Create an exoplayer instance and start playing video
        buildPlayer(mp4Url);

    }

    private void buildPlayer(String mp4Url) {
        // Create a default TrackSelector
        Handler mainHandler = new Handler();
        BandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();
        TrackSelection.Factory videoTrackSelectionFactory = new AdaptiveTrackSelection.Factory(bandwidthMeter);
        TrackSelector trackSelector = new DefaultTrackSelector(videoTrackSelectionFactory);

        // Create the player
        exoPlayer = ExoPlayerFactory.newSimpleInstance(this, trackSelector); // no LoadControl?
        simpleExoPlayerView = new SimpleExoPlayerView(this);
        simpleExoPlayerView = (SimpleExoPlayerView) findViewById(R.id.player_view);

        // Set media controller
        simpleExoPlayerView.setUseController(true);
        simpleExoPlayerView.requestFocus();

        // Bind player to the view
        simpleExoPlayerView.setPlayer(exoPlayer);

        // Create Uri from video location
        // TODO: should this be in some network class? Should I be appending APIKEY here?
        Uri mp4Uri = Uri.parse(mp4Url + "?api_key=" + BuildConfig.GIANTBOMB_API_KEY);
        Timber.v("Video url with api key: " + mp4Uri.toString());

        // Create another bandwidth meter for bandwidth during playback (not strictly necessary)
        DefaultBandwidthMeter playbackBandwidthMeter = new DefaultBandwidthMeter();

        // DataSourceFactory to produce DataSource instances through which media data is loaded
        DefaultDataSourceFactory dataSourceFactory = new DefaultDataSourceFactory(this,
                Util.getUserAgent(this, "GiantBombForAndroid"),
                playbackBandwidthMeter);

        // Produces Extractor instances for parsing the media data
        ExtractorsFactory extractorsFactory = new DefaultExtractorsFactory();

        ExtractorMediaSource.EventListener eventListener = new ExtractorMediaSource.EventListener() {
            @Override
            public void onLoadError(IOException error) {
                Timber.e("Error loading video from source");
            }
        };

        final MediaSource videoSource = new ExtractorMediaSource(mp4Uri,
                dataSourceFactory,
                extractorsFactory,
                mainHandler,
                eventListener);

        exoPlayer.prepare(videoSource);

        exoPlayer.addListener(new ExoPlayer.EventListener() {
            @Override
            public void onLoadingChanged(boolean isLoading) {
                Timber.v("Listener-onLoadingChanged...");

            }

            @Override
            public void onPlayerStateChanged(boolean playWhenReady, int playbackState) {
                Timber.v("Listener-onPlayerStateChanged...");

            }

            @Override
            public void onTimelineChanged(Timeline timeline, Object manifest) {
                Timber.v("Listener-onTimelineChanged...");

            }

            @Override
            public void onTracksChanged(TrackGroupArray trackGroups, TrackSelectionArray trackSelections) {
                // TODO: Do I need anything here?
            }

            @Override
            public void onPlayerError(ExoPlaybackException error) {
                Timber.v("Listener-onPlayerError...");
                exoPlayer.stop();
                exoPlayer.prepare(videoSource);
                exoPlayer.setPlayWhenReady(true);
            }

            @Override
            public void onPositionDiscontinuity() {
                Timber.v("Listener-onPositionDiscontinuity...");

            }

            @Override
            public void onPlaybackParametersChanged(PlaybackParameters playbackParameters) {
                // TODO: Do I need anything here?
            }
        });
        exoPlayer.setPlayWhenReady(true);
    }

    @Override
    protected void onStart() {
        super.onStart();
        Timber.v("onStart()...");
        if (exoPlayer == null) {
            Timber.v("No exoplayer instance, recreating...");
            buildPlayer(mp4Url);
            exoPlayer.seekTo(playerPosition);
        }
    }

    @Override
    protected void onStop(){
        super.onStop();
        Timber.v("onStop()...");
        //TODO: pull player creation code into it's own method so it can be called here as well
        playerPosition = exoPlayer.getCurrentPosition();
        exoPlayer.release();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Timber.v("onDestroy()...");
        exoPlayer.release();
    }
}

Answer 1

目前您正在 onStop() 中调用 release，这将清空播放器的所有重要部分，但不会清空 exoPlayer 字段(并销毁任何状态你没有跟踪自己)。

有几种不同的方法。但无论您做什么，您都可能希望自己跟踪某些状态。下面我将它们用作字段，但它们也可以放在 onSavedInstanceState() 中。在 onStop() 中，我们保存了两条信息，然后在 onStart() 中将它们提取出来。 1) 我们的玩家在暂停时所处的最后位置，以及 2) 我们是否应该在恢复时播放。您可以将 seekTo 调用移出 if == null block ，因为您可能总是希望从中断的地方继续。:

@Override
public void onStart() {
    // ...

    if (exoPlayer == null) {
        // init player
    }

    // Seek to the last position of the player.
    exoPlayer.seekTo(mLastPosition);

    // Put the player into the last state we were in.
    exoPlayer.setPlayWhenReady(mPlayVideoWhenForegrounded);

    // ...
}

@Override
public void onStop() {
    // ...

    // Store off if we were playing so we know if we should start when we're foregrounded again.
    mPlayVideoWhenForegrounded = exoPlayer.getPlayWhenReady();

    // Store off the last position our player was in before we paused it.
    mLastPosition = exoPlayer.getCurrentPosition();

    // Pause the player
    exoPlayer.setPlayWhenReady(false);

    // ...
}

现在我在您的代码示例中看到的另一个问题是 exoPlayer.release() 不会清空 exoPlayer 字段。因此，您可以在 exoPlayer.release() 之后添加 exoPlayer = null 行，这有望解决您的多个 exoPlayer 问题。您还可以将 release() 调用移动到 onDestroy()，但前提是您知道自己正在正确地重新实例化所有内容。