Add remote volume slider to sound settings

1. Add RemoteVolumePreferenceController to control volume through
MediaSessions.
2. Add related preference to skip calling AudioManager.

Bug: 126199571
Test: RunSettingsRoboTests
Change-Id: I9cb85ccf5f49be6d127cb61caf445b2ee7dfb579

src/com/android/settings/notification/RemoteVolumePreferenceController.java

@@ -0,0 +1,159 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.notification;
+
+import android.content.Context;
+import android.media.session.MediaController;
+import android.media.session.MediaSession;
+import android.media.session.MediaSessionManager;
+import android.os.Looper;
+import android.text.TextUtils;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.lifecycle.OnLifecycleEvent;
+
+import com.android.settings.R;
+import com.android.settingslib.core.lifecycle.Lifecycle;
+import com.android.settingslib.volume.MediaSessions;
+
+import java.util.List;
+
+public class RemoteVolumePreferenceController extends
+    VolumeSeekBarPreferenceController {
+
+    private static final String KEY_REMOTE_VOLUME = "remote_volume";
+    @VisibleForTesting
+    static final int REMOTE_VOLUME = 100;
+
+    private MediaSessionManager mMediaSessionManager;
+    private MediaSessions mMediaSessions;
+    private MediaSession.Token mActiveToken;
+
+    private MediaSessions.Callbacks mCallbacks = new MediaSessions.Callbacks() {
+        @Override
+        public void onRemoteUpdate(MediaSession.Token token, String name,
+                MediaController.PlaybackInfo pi) {
+            mActiveToken = token;
+            mPreference.setMax(pi.getMaxVolume());
+            mPreference.setVisible(true);
+            setSliderPosition(pi.getCurrentVolume());
+        }
+
+        @Override
+        public void onRemoteRemoved(MediaSession.Token t) {
+            if (mActiveToken == t) {
+                mActiveToken = null;
+                mPreference.setVisible(false);
+            }
+        }
+
+        @Override
+        public void onRemoteVolumeChanged(MediaSession.Token token, int flags) {
+            if (mActiveToken == token) {
+                final MediaController mediaController = new MediaController(mContext, token);
+                final MediaController.PlaybackInfo pi = mediaController.getPlaybackInfo();
+                setSliderPosition(pi.getCurrentVolume());
+            }
+        }
+    };
+
+    public RemoteVolumePreferenceController(Context context) {
+        super(context, KEY_REMOTE_VOLUME);
+        mMediaSessionManager = context.getSystemService(MediaSessionManager.class);
+        mMediaSessions = new MediaSessions(context, Looper.getMainLooper(), mCallbacks);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        final List<MediaController> controllers = mMediaSessionManager.getActiveSessions(null);
+        for (MediaController mediaController : controllers) {
+            final MediaController.PlaybackInfo pi = mediaController.getPlaybackInfo();
+            if (isRemote(pi)) {
+                mActiveToken = mediaController.getSessionToken();
+                return AVAILABLE;
+            }
+        }
+
+        // No active remote media at this point
+        return CONDITIONALLY_UNAVAILABLE;
+    }
+
+    @OnLifecycleEvent(Lifecycle.Event.ON_RESUME)
+    public void onResume() {
+        super.onResume();
+        mMediaSessions.init();
+    }
+
+    @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)
+    public void onPause() {
+        super.onPause();
+        mMediaSessions.destroy();
+    }
+
+    @Override
+    public int getSliderPosition() {
+        if (mPreference != null) {
+            return mPreference.getProgress();
+        }
+        //TODO(b/126199571): get it from media controller
+        return 0;
+    }
+
+    @Override
+    public boolean setSliderPosition(int position) {
+        if (mPreference != null) {
+            mPreference.setProgress(position);
+        }
+        //TODO(b/126199571): set it through media controller
+        return false;
+    }
+
+    @Override
+    public int getMaxSteps() {
+        if (mPreference != null) {
+            return mPreference.getMax();
+        }
+        //TODO(b/126199571): get it from media controller
+        return 0;
+    }
+
+    @Override
+    public boolean isSliceable() {
+        return TextUtils.equals(getPreferenceKey(), KEY_REMOTE_VOLUME);
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return KEY_REMOTE_VOLUME;
+    }
+
+    @Override
+    public int getAudioStream() {
+        // This can be anything because remote volume controller doesn't rely on it.
+        return REMOTE_VOLUME;
+    }
+
+    @Override
+    public int getMuteIcon() {
+        return R.drawable.ic_volume_remote_mute;
+    }
+
+    public static boolean isRemote(MediaController.PlaybackInfo pi) {
+        return pi != null
+                && pi.getPlaybackType() == MediaController.PlaybackInfo.PLAYBACK_TYPE_REMOTE;
+    }
+}