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管理 TV 用户交互

在直播电视体验中，用户切换频道并看到频道和节目信息暂时消失不见。其他类型的信息如消息（“请勿在家模仿”）、字幕或广告，您可能需要一直保留该状态。与任何电视一样应用，此类信息不应干扰屏幕上播放的节目内容。

图 1. 直播电视应用中的叠加消息。

另外，请考虑是否应该展示某些节目内容，内容分级和家长控制设置，以及应用的行为及通知用户的行为内容遭到屏蔽或无法播放。本课介绍如何开发 TV 输入来了解这些注意事项。

将播放器与 Surface 集成

您的 TV 输入必须将视频渲染到 Surface 对象上，该对象会通过 TvInputService.Session.onSetSurface() 方法。以下示例展示了如何使用 MediaPlayer 实例来玩游戏 Surface 对象中的内容：

Kotlin

override fun onSetSurface(surface: Surface?): Boolean {
    player?.setSurface(surface)
    mSurface = surface
    return true
}

override fun onSetStreamVolume(volume: Float) {
    player?.setVolume(volume, volume)
    mVolume = volume
}

Java

@Override
public boolean onSetSurface(Surface surface) {
    if (player != null) {
        player.setSurface(surface);
    }
    mSurface = surface;
    return true;
}

@Override
public void onSetStreamVolume(float volume) {
    if (player != null) {
        player.setVolume(volume, volume);
    }
    mVolume = volume;
}

同样，下面说明了如何使用 ExoPlayer：

Kotlin

override fun onSetSurface(surface: Surface?): Boolean {
    player?.createMessage(videoRenderer)?.apply {
        type = MSG_SET_SURFACE
        payload = surface
        send()
    }
    mSurface = surface
    return true
}

override fun onSetStreamVolume(volume: Float) {
    player?.createMessage(audioRenderer)?.apply {
        type = MSG_SET_VOLUME
        payload = volume
        send()
    }
    mVolume = volume
}

Java

@Override
public boolean onSetSurface(@Nullable Surface surface) {
    if (player != null) {
        player.createMessage(videoRenderer)
                .setType(MSG_SET_SURFACE)
                .setPayload(surface)
                .send();
    }
    mSurface = surface;
    return true;
}

@Override
public void onSetStreamVolume(float volume) {
    if (player != null) {
        player.createMessage(videoRenderer)
                .setType(MSG_SET_VOLUME)
                .setPayload(volume)
                .send();
    }
    mVolume = volume;
}

使用叠加层

您可以使用叠加层来显示字幕、消息、广告或 MHEG-5 数据广播。默认情况下，叠加层已停用。您可以在创建会话时通过调用 TvInputService.Session.setOverlayViewEnabled(true), 如以下示例中所示：

Kotlin

override fun onCreateSession(inputId: String): Session =
        onCreateSessionInternal(inputId).apply {
            setOverlayViewEnabled(true)
            sessions.add(this)
        }

Java

@Override
public final Session onCreateSession(String inputId) {
    BaseTvInputSessionImpl session = onCreateSessionInternal(inputId);
    session.setOverlayViewEnabled(true);
    sessions.add(session);
    return session;
}

对叠加层使用从 TvInputService.Session.onCreateOverlayView() 返回的 View 对象，如下所示：

Kotlin

override fun onCreateOverlayView(): View =
        (context.getSystemService(LAYOUT_INFLATER_SERVICE) as LayoutInflater).run {
            inflate(R.layout.overlayview, null).apply {
                subtitleView = findViewById<SubtitleView>(R.id.subtitles).apply {
                    // Configure the subtitle view.
                    val captionStyle: CaptionStyleCompat =
                            CaptionStyleCompat.createFromCaptionStyle(captioningManager.userStyle)
                    setStyle(captionStyle)
                    setFractionalTextSize(captioningManager.fontScale)
                }
            }
        }

Java

@Override
public View onCreateOverlayView() {
    LayoutInflater inflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
    View view = inflater.inflate(R.layout.overlayview, null);
    subtitleView = (SubtitleView) view.findViewById(R.id.subtitles);

    // Configure the subtitle view.
    CaptionStyleCompat captionStyle;
    captionStyle = CaptionStyleCompat.createFromCaptionStyle(
            captioningManager.getUserStyle());
    subtitleView.setStyle(captionStyle);
    subtitleView.setFractionalTextSize(captioningManager.fontScale);
    return view;
}

叠加层的布局定义可能如下所示：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.exoplayer.text.SubtitleView
        android:id="@+id/subtitles"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|center_horizontal"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginBottom="32dp"
        android:visibility="invisible"/>
</FrameLayout>

控制内容

当用户选择某个频道时，您的 TV 输入会处理 TvInputService.Session 对象中的 onTune() 回调。系统 TV 应用的家长控制功能会根据内容分级来决定显示哪些内容。以下各部分介绍了如何使用 TvInputService.Session notify 方法与系统 TV 应用通信。

让视频无法播放

当用户更改频道时，您需要确保屏幕不会显示任何散乱的画面。在 TV 输入呈现内容时再呈现视频伪影。调用 TvInputService.Session.onTune() 时：您可以调用 TvInputService.Session.notifyVideoUnavailable() 来阻止显示该视频并传递 VIDEO_UNAVAILABLE_REASON_TUNING 常量，如如以下示例中所示。

Kotlin

override fun onTune(channelUri: Uri): Boolean {
    subtitleView?.visibility = View.INVISIBLE
    notifyVideoUnavailable(TvInputManager.VIDEO_UNAVAILABLE_REASON_TUNING)
    unblockedRatingSet.clear()

    dbHandler.apply {
        removeCallbacks(playCurrentProgramRunnable)
        playCurrentProgramRunnable = PlayCurrentProgramRunnable(channelUri)
        post(playCurrentProgramRunnable)
    }
    return true
}

Java

@Override
public boolean onTune(Uri channelUri) {
    if (subtitleView != null) {
        subtitleView.setVisibility(View.INVISIBLE);
    }
    notifyVideoUnavailable(TvInputManager.VIDEO_UNAVAILABLE_REASON_TUNING);
    unblockedRatingSet.clear();

    dbHandler.removeCallbacks(playCurrentProgramRunnable);
    playCurrentProgramRunnable = new PlayCurrentProgramRunnable(channelUri);
    dbHandler.post(playCurrentProgramRunnable);
    return true;
}

然后，当内容渲染到 Surface 时，调用 TvInputService.Session.notifyVideoAvailable() 以允许视频显示，如下所示：

Kotlin

fun onRenderedFirstFrame(surface:Surface) {
    firstFrameDrawn = true
    notifyVideoAvailable()
}

Java

@Override
public void onRenderedFirstFrame(Surface surface) {
    firstFrameDrawn = true;
    notifyVideoAvailable();
}

这种过渡仅持续几分几秒，但呈现空白屏幕会这要比让图片闪烁奇怪的闪烁和抖动的效果要好。

如需详细了解如何使用 Surface，另请参阅将播放器与 Surface 集成。并��用 Surface 呈现视频。

提供家长控制

如需确定特定内容是否因家长控制功能和内容分级而被禁播，您可以查看 TvInputManager 类方法，isParentalControlsEnabled() 和 isRatingBlocked(android.media.tv.TvContentRating)。您可能还需要确保内容的 TvContentRating 包含在一组当前允许的内容分级。以下示例显示了这些考虑因素。

Kotlin

private fun checkContentBlockNeeded() {
    currentContentRating?.also { rating ->
        if (!tvInputManager.isParentalControlsEnabled
                || !tvInputManager.isRatingBlocked(rating)
                || unblockedRatingSet.contains(rating)) {
            // Content rating is changed so we don't need to block anymore.
            // Unblock content here explicitly to resume playback.
            unblockContent(null)
            return
        }
    }
    lastBlockedRating = currentContentRating
    player?.run {
        // Children restricted content might be blocked by TV app as well,
        // but TIF should do its best not to show any single frame of blocked content.
        releasePlayer()
    }

    notifyContentBlocked(currentContentRating)
}

Java

private void checkContentBlockNeeded() {
    if (currentContentRating == null || !tvInputManager.isParentalControlsEnabled()
            || !tvInputManager.isRatingBlocked(currentContentRating)
            || unblockedRatingSet.contains(currentContentRating)) {
        // Content rating is changed so we don't need to block anymore.
        // Unblock content here explicitly to resume playback.
        unblockContent(null);
        return;
    }

    lastBlockedRating = currentContentRating;
    if (player != null) {
        // Children restricted content might be blocked by TV app as well,
        // but TIF should do its best not to show any single frame of blocked content.
        releasePlayer();
    }

    notifyContentBlocked(currentContentRating);
}

确定是否应屏蔽相应内容后，请通知系统 TV 调用 TvInputService.Session 方法 notifyContentAllowed() 或 notifyContentBlocked() ，如上例所示。

使用 TvContentRating 类生成系统定义的字符串包含COLUMN_CONTENT_RATING TvContentRating.createRating() 方法，如下所示：

Kotlin

val rating = TvContentRating.createRating(
        "com.android.tv",
        "US_TV",
        "US_TV_PG",
        "US_TV_D", "US_TV_L"
)

Java

TvContentRating rating = TvContentRating.createRating(
    "com.android.tv",
    "US_TV",
    "US_TV_PG",
    "US_TV_D", "US_TV_L");

处理轨道选择

TvTrackInfo 类包含有关以下媒体轨道的信息：作为轨道类型（视频、音频或字幕），等等。

您的 TV 输入会话第一次能够获取曲目信息时，应调用将 TvInputService.Session.notifyTracksChanged() 替换为用于更新系统 TV 应用的所有轨道的列表。何时轨道信息发生了变化，调用 notifyTracksChanged() 以更新系统。

系统 TV 应用会提供一个界面，以便用户在有多个轨道时选择特定轨道指定轨道类型可以使用哪些轨道；例如不同语言的字幕你的电视会响应 onSelectTrack() 从系统 TV 应用调用 notifyTrackSelected() ，如以下示例所示。请注意，当 null 时，作为轨道 ID 传递，这将取消选择相应轨道。

Kotlin

override fun onSelectTrack(type: Int, trackId: String?): Boolean =
        mPlayer?.let { player ->
            if (type == TvTrackInfo.TYPE_SUBTITLE) {
                if (!captionEnabled && trackId != null) return false
                selectedSubtitleTrackId = trackId
                subtitleView.visibility = if (trackId == null) View.INVISIBLE else View.VISIBLE
            }
            player.trackInfo.indexOfFirst { it.trackType == type }.let { trackIndex ->
                if( trackIndex >= 0) {
                    player.selectTrack(trackIndex)
                    notifyTrackSelected(type, trackId)
                    true
                } else false
            }
        } ?: false

Java

@Override
public boolean onSelectTrack(int type, String trackId) {
    if (player != null) {
        if (type == TvTrackInfo.TYPE_SUBTITLE) {
            if (!captionEnabled && trackId != null) {
                return false;
            }
            selectedSubtitleTrackId = trackId;
            if (trackId == null) {
                subtitleView.setVisibility(View.INVISIBLE);
            }
        }
        int trackIndex = -1;
        MediaPlayer.TrackInfo[] trackInfos = player.getTrackInfo();
        for (int index = 0; index < trackInfos.length; index++) {
            MediaPlayer.TrackInfo trackInfo = trackInfos[index];
            if (trackInfo.getTrackType() == type) {
                trackIndex = index;
                break;
            }
        }
        if (trackIndex >= 0) {
            player.selectTrack(trackIndex);
            notifyTrackSelected(type, trackId);
            return true;
        }
    }
    return false;
}

使用频道数据

支持时移