media/browse/MediaBrowser.java

/*
 * Copyright (C) 2014 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 android.media.browse;

import android.annotation.IntDef;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.content.pm.ParceledListSlice;
import android.media.MediaDescription;
import android.media.session.MediaController;
import android.media.session.MediaSession;
import android.os.Binder;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Parcel;
import android.os.Parcelable;
import android.os.RemoteException;
import android.os.ResultReceiver;
import android.service.media.IMediaBrowserService;
import android.service.media.IMediaBrowserServiceCallbacks;
import android.service.media.MediaBrowserService;
import android.text.TextUtils;
import android.util.ArrayMap;
import android.util.Log;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.List;
import java.util.Map.Entry;

/**
 * Browses media content offered by a link MediaBrowserService.
 * <p>
 * This object is not thread-safe. All calls should happen on the thread on which the browser
 * was constructed.
 * </p>
 * <h3>Standard Extra Data</h3>
 *
 * <p>These are the current standard fields that can be used as extra data via
 * {@link #subscribe(String, Bundle, SubscriptionCallback)},
 * {@link #unsubscribe(String, SubscriptionCallback)}, and
 * {@link SubscriptionCallback#onChildrenLoaded(String, List, Bundle)}.
 *
 * <ul>
 *     <li> {@link #EXTRA_PAGE}
 *     <li> {@link #EXTRA_PAGE_SIZE}
 * </ul>
 */
public final class MediaBrowser {
    private static final String TAG = "MediaBrowser";
    private static final boolean DBG = false;

    /**
     * Used as an int extra field to denote the page number to subscribe.
     * The value of {@code EXTRA_PAGE} should be greater than or equal to 0.
     *
     * @see #EXTRA_PAGE_SIZE
     */
    public static final String EXTRA_PAGE = "android.media.browse.extra.PAGE";

    /**
     * Used as an int extra field to denote the number of media items in a page.
     * The value of {@code EXTRA_PAGE_SIZE} should be greater than or equal to 1.
     *
     * @see #EXTRA_PAGE
     */
    public static final String EXTRA_PAGE_SIZE = "android.media.browse.extra.PAGE_SIZE";

    private static final int CONNECT_STATE_DISCONNECTING = 0;
    private static final int CONNECT_STATE_DISCONNECTED = 1;
    private static final int CONNECT_STATE_CONNECTING = 2;
    private static final int CONNECT_STATE_CONNECTED = 3;
    private static final int CONNECT_STATE_SUSPENDED = 4;

    private final Context mContext;
    private final ComponentName mServiceComponent;
    private final ConnectionCallback mCallback;
    private final Bundle mRootHints;
    private final Handler mHandler = new Handler();
    private final ArrayMap<String, Subscription> mSubscriptions = new ArrayMap<>();

    private volatile int mState = CONNECT_STATE_DISCONNECTED;
    private volatile String mRootId;
    private volatile MediaSession.Token mMediaSessionToken;
    private volatile Bundle mExtras;

    private MediaServiceConnection mServiceConnection;
    private IMediaBrowserService mServiceBinder;
    private IMediaBrowserServiceCallbacks mServiceCallbacks;

    /**
     * Creates a media browser for the specified media browser service.
     *
     * @param context The context.
     * @param serviceComponent The component name of the media browser service.
     * @param callback The connection callback.
     * @param rootHints An optional bundle of service-specific arguments to send
     * to the media browser service when connecting and retrieving the root id
     * for browsing, or null if none. The contents of this bundle may affect
     * the information returned when browsing.
     * @see android.service.media.MediaBrowserService.BrowserRoot#EXTRA_RECENT
     * @see android.service.media.MediaBrowserService.BrowserRoot#EXTRA_OFFLINE
     * @see android.service.media.MediaBrowserService.BrowserRoot#EXTRA_SUGGESTED
     */
    public MediaBrowser(Context context, ComponentName serviceComponent,
            ConnectionCallback callback, Bundle rootHints) {
        if (context == null) {
            throw new IllegalArgumentException("context must not be null");
        }
        if (serviceComponent == null) {
            throw new IllegalArgumentException("service component must not be null");
        }
        if (callback == null) {
            throw new IllegalArgumentException("connection callback must not be null");
        }
        mContext = context;
        mServiceComponent = serviceComponent;
        mCallback = callback;
        mRootHints = rootHints == null ? null : new Bundle(rootHints);
    }

    /**
     * Connects to the media browser service.
     * <p>
     * The connection callback specified in the constructor will be invoked
     * when the connection completes or fails.
     * </p>
     */
    public void connect() {
        if (mState != CONNECT_STATE_DISCONNECTING && mState != CONNECT_STATE_DISCONNECTED) {
            throw new IllegalStateException("connect() called while neither disconnecting nor "
                    + "disconnected (state=" + getStateLabel(mState) + ")");
        }

        mState = CONNECT_STATE_CONNECTING;
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                if (mState == CONNECT_STATE_DISCONNECTING) {
                    return;
                }
                mState = CONNECT_STATE_CONNECTING;
                // TODO: remove this extra check.
                if (DBG) {
                    if (mServiceConnection != null) {
                        throw new RuntimeException("mServiceConnection should be null. Instead it"
                                + " is " + mServiceConnection);
                    }
                }
                if (mServiceBinder != null) {
                    throw new RuntimeException("mServiceBinder should be null. Instead it is "
                            + mServiceBinder);
                }
                if (mServiceCallbacks != null) {
                    throw new RuntimeException("mServiceCallbacks should be null. Instead it is "
                            + mServiceCallbacks);
                }

                final Intent intent = new Intent(MediaBrowserService.SERVICE_INTERFACE);
                intent.setComponent(mServiceComponent);

                mServiceConnection = new MediaServiceConnection();

                boolean bound = false;
                try {
                    bound = mContext.bindService(intent, mServiceConnection,
                            Context.BIND_AUTO_CREATE);
                } catch (Exception ex) {
                    Log.e(TAG, "Failed binding to service " + mServiceComponent);
                }

                if (!bound) {
                    // Tell them that it didn't work.
                    forceCloseConnection();
                    mCallback.onConnectionFailed();
                }

                if (DBG) {
                    Log.d(TAG, "connect...");
                    dump();
                }
            }
        });
    }

    /**
     * Disconnects from the media browser service.
     * After this, no more callbacks will be received.
     */
    public void disconnect() {
        // It's ok to call this any state, because allowing this lets apps not have
        // to check isConnected() unnecessarily. They won't appreciate the extra
        // assertions for this. We do everything we can here to go back to a sane state.
        mState = CONNECT_STATE_DISCONNECTING;
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                // connect() could be called before this. Then we will disconnect and reconnect.
                if (mServiceCallbacks != null) {
                    try {
                        mServiceBinder.disconnect(mServiceCallbacks);
                    } catch (RemoteException ex) {
                        // We are disconnecting anyway. Log, just for posterity but it's not
                        // a big problem.
                        Log.w(TAG, "RemoteException during connect for " + mServiceComponent);
                    }
                }
                int state = mState;
                forceCloseConnection();
                // If the state was not CONNECT_STATE_DISCONNECTING, keep the state so that
                // the operation came after disconnect() can be handled properly.
                if (state != CONNECT_STATE_DISCONNECTING) {
                    mState = state;
                }
                if (DBG) {
                    Log.d(TAG, "disconnect...");
                    dump();
                }
            }
        });
    }

    /**
     * Null out the variables and unbind from the service. This doesn't include
     * calling disconnect on the service, because we only try to do that in the
     * clean shutdown cases.
     * <p>
     * Everywhere that calls this EXCEPT for disconnect() should follow it with
     * a call to mCallback.onConnectionFailed(). Disconnect doesn't do that callback
     * for a clean shutdown, but everywhere else is a dirty shutdown and should
     * notify the app.
     * <p>
     * Also, mState should be updated properly. Mostly it should be CONNECT_STATE_DIACONNECTED
     * except for disconnect().
     */
    private void forceCloseConnection() {
        if (mServiceConnection != null) {
            try {
                mContext.unbindService(mServiceConnection);
            } catch (IllegalArgumentException e) {
                if (DBG) {
                    Log.d(TAG, "unbindService failed", e);
                }
            }
        }
        mState = CONNECT_STATE_DISCONNECTED;
        mServiceConnection = null;
        mServiceBinder = null;
        mServiceCallbacks = null;
        mRootId = null;
        mMediaSessionToken = null;
    }

    /**
     * Returns whether the browser is connected to the service.
     */
    public boolean isConnected() {
        return mState == CONNECT_STATE_CONNECTED;
    }

    /**
     * Gets the service component that the media browser is connected to.
     */
    public @NonNull ComponentName getServiceComponent() {
        if (!isConnected()) {
            throw new IllegalStateException("getServiceComponent() called while not connected" +
                    " (state=" + mState + ")");
        }
        return mServiceComponent;
    }

    /**
     * Gets the root id.
     * <p>
     * Note that the root id may become invalid or change when the
     * browser is disconnected.
     * </p>
     *
     * @throws IllegalStateException if not connected.
     */
    public @NonNull String getRoot() {
        if (!isConnected()) {
            throw new IllegalStateException("getRoot() called while not connected (state="
                    + getStateLabel(mState) + ")");
        }
        return mRootId;
    }

    /**
     * Gets any extras for the media service.
     *
     * @throws IllegalStateException if not connected.
     */
    public @Nullable Bundle getExtras() {
        if (!isConnected()) {
            throw new IllegalStateException("getExtras() called while not connected (state="
                    + getStateLabel(mState) + ")");
        }
        return mExtras;
    }

    /**
     * Gets the media session token associated with the media browser.
     * <p>
     * Note that the session token may become invalid or change when the
     * browser is disconnected.
     * </p>
     *
     * @return The session token for the browser, never null.
     *
     * @throws IllegalStateException if not connected.
     */
     public @NonNull MediaSession.Token getSessionToken() {
        if (!isConnected()) {
            throw new IllegalStateException("getSessionToken() called while not connected (state="
                    + mState + ")");
        }
        return mMediaSessionToken;
    }

    /**
     * Queries for information about the media items that are contained within
     * the specified id and subscribes to receive updates when they change.
     * <p>
     * The list of subscriptions is maintained even when not connected and is
     * restored after the reconnection. It is ok to subscribe while not connected
     * but the results will not be returned until the connection completes.
     * </p>
     * <p>
     * If the id is already subscribed with a different callback then the new
     * callback will replace the previous one and the child data will be
     * reloaded.
     * </p>
     *
     * @param parentId The id of the parent media item whose list of children
     *            will be subscribed.
     * @param callback The callback to receive the list of children.
     */
    public void subscribe(@NonNull String parentId, @NonNull SubscriptionCallback callback) {
        subscribeInternal(parentId, null, callback);
    }

    /**
     * Queries with service-specific arguments for information about the media items
     * that are contained within the specified id and subscribes to receive updates
     * when they change.
     * <p>
     * The list of subscriptions is maintained even when not connected and is
     * restored after the reconnection. It is ok to subscribe while not connected
     * but the results will not be returned until the connection completes.
     * </p>
     * <p>
     * If the id is already subscribed with a different callback then the new
     * callback will replace the previous one and the child data will be
     * reloaded.
     * </p>
     *
     * @param parentId The id of the parent media item whose list of children
     *            will be subscribed.
     * @param options The bundle of service-specific arguments to send to the media
     *            browser service. The contents of this bundle may affect the
     *            information returned when browsing.
     * @param callback The callback to receive the list of children.
     */
    public void subscribe(@NonNull String parentId, @NonNull Bundle options,
            @NonNull SubscriptionCallback callback) {
        if (options == null) {
            throw new IllegalArgumentException("options cannot be null");
        }
        subscribeInternal(parentId, new Bundle(options), callback);
    }

    /**
     * Unsubscribes for changes to the children of the specified media id.
     * <p>
     * The query callback will no longer be invoked for results associated with
     * this id once this method returns.
     * </p>
     *
     * @param parentId The id of the parent media item whose list of children
     *            will be unsubscribed.
     */
    public void unsubscribe(@NonNull String parentId) {
        unsubscribeInternal(parentId, null);
    }

    /**
     * Unsubscribes for changes to the children of the specified media id through a callback.
     * <p>
     * The query callback will no longer be invoked for results associated with
     * this id once this method returns.
     * </p>
     *
     * @param parentId The id of the parent media item whose list of children
     *            will be unsubscribed.
     * @param callback A callback sent to the media browser service to subscribe.
     */
    public void unsubscribe(@NonNull String parentId, @NonNull SubscriptionCallback callback) {
        if (callback == null) {
            throw new IllegalArgumentException("callback cannot be null");
        }
        unsubscribeInternal(parentId, callback);
    }

    /**
     * Retrieves a specific {@link MediaItem} from the connected service. Not
     * all services may support this, so falling back to subscribing to the
     * parent's id should be used when unavailable.
     *
     * @param mediaId The id of the item to retrieve.
     * @param cb The callback to receive the result on.
     */
    public void getItem(final @NonNull String mediaId, @NonNull final ItemCallback cb) {
        if (TextUtils.isEmpty(mediaId)) {
            throw new IllegalArgumentException("mediaId cannot be empty.");
        }
        if (cb == null) {
            throw new IllegalArgumentException("cb cannot be null.");
        }
        if (mState != CONNECT_STATE_CONNECTED) {
            Log.i(TAG, "Not connected, unable to retrieve the MediaItem.");
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    cb.onError(mediaId);
                }
            });
            return;
        }
        ResultReceiver receiver = new ResultReceiver(mHandler) {
            @Override
            protected void onReceiveResult(int resultCode, Bundle resultData) {
                if (!isConnected()) {
                    return;
                }
                if (resultCode != 0 || resultData == null
                        || !resultData.containsKey(MediaBrowserService.KEY_MEDIA_ITEM)) {
                    cb.onError(mediaId);
                    return;
                }
                Parcelable item = resultData.getParcelable(MediaBrowserService.KEY_MEDIA_ITEM);
                if (item != null && !(item instanceof MediaItem)) {
                    cb.onError(mediaId);
                    return;
                }
                cb.onItemLoaded((MediaItem)item);
            }
        };
        try {
            mServiceBinder.getMediaItem(mediaId, receiver, mServiceCallbacks);
        } catch (RemoteException e) {
            Log.i(TAG, "Remote error getting media item.");
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    cb.onError(mediaId);
                }
            });
        }
    }

    private void subscribeInternal(String parentId, Bundle options, SubscriptionCallback callback) {
        // Check arguments.
        if (TextUtils.isEmpty(parentId)) {
            throw new IllegalArgumentException("parentId cannot be empty.");
        }
        if (callback == null) {
            throw new IllegalArgumentException("callback cannot be null");
        }
        // Update or create the subscription.
        Subscription sub = mSubscriptions.get(parentId);
        if (sub == null) {
            sub = new Subscription();
            mSubscriptions.put(parentId, sub);
        }
        sub.putCallback(options, callback);

        // If we are connected, tell the service that we are watching. If we aren't connected,
        // the service will be told when we connect.
        if (isConnected()) {
            try {
                if (options == null) {
                    mServiceBinder.addSubscriptionDeprecated(parentId, mServiceCallbacks);
                }
                mServiceBinder.addSubscription(parentId, callback.mToken, options,
                        mServiceCallbacks);
            } catch (RemoteException ex) {
                // Process is crashing. We will disconnect, and upon reconnect we will
                // automatically reregister. So nothing to do here.
                Log.d(TAG, "addSubscription failed with RemoteException parentId=" + parentId);
            }
        }
    }

    private void unsubscribeInternal(String parentId, SubscriptionCallback callback) {
        // Check arguments.
        if (TextUtils.isEmpty(parentId)) {
            throw new IllegalArgumentException("parentId cannot be empty.");
        }

        Subscription sub = mSubscriptions.get(parentId);
        if (sub == null) {
            return;
        }
        // Tell the service if necessary.
        try {
            if (callback == null) {
                if (isConnected()) {
                    mServiceBinder.removeSubscriptionDeprecated(parentId, mServiceCallbacks);
                    mServiceBinder.removeSubscription(parentId, null, mServiceCallbacks);
                }
            } else {
                final List<SubscriptionCallback> callbacks = sub.getCallbacks();
                final List<Bundle> optionsList = sub.getOptionsList();
                for (int i = callbacks.size() - 1; i >= 0; --i) {
                    if (callbacks.get(i) == callback) {
                        if (isConnected()) {
                            mServiceBinder.removeSubscription(
                                    parentId, callback.mToken, mServiceCallbacks);
                        }
                        callbacks.remove(i);
                        optionsList.remove(i);
                    }
                }
            }
        } catch (RemoteException ex) {
            // Process is crashing. We will disconnect, and upon reconnect we will
            // automatically reregister. So nothing to do here.
            Log.d(TAG, "removeSubscription failed with RemoteException parentId=" + parentId);
        }

        if (sub.isEmpty() || callback == null) {
            mSubscriptions.remove(parentId);
        }
    }

    /**
     * For debugging.
     */
    private static String getStateLabel(int state) {
        switch (state) {
            case CONNECT_STATE_DISCONNECTING:
                return "CONNECT_STATE_DISCONNECTING";
            case CONNECT_STATE_DISCONNECTED:
                return "CONNECT_STATE_DISCONNECTED";
            case CONNECT_STATE_CONNECTING:
                return "CONNECT_STATE_CONNECTING";
            case CONNECT_STATE_CONNECTED:
                return "CONNECT_STATE_CONNECTED";
            case CONNECT_STATE_SUSPENDED:
                return "CONNECT_STATE_SUSPENDED";
            default:
                return "UNKNOWN/" + state;
        }
    }

    private final void onServiceConnected(final IMediaBrowserServiceCallbacks callback,
            final String root, final MediaSession.Token session, final Bundle extra) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                // Check to make sure there hasn't been a disconnect or a different
                // ServiceConnection.
                if (!isCurrent(callback, "onConnect")) {
                    return;
                }
                // Don't allow them to call us twice.
                if (mState != CONNECT_STATE_CONNECTING) {
                    Log.w(TAG, "onConnect from service while mState="
                            + getStateLabel(mState) + "... ignoring");
                    return;
                }
                mRootId = root;
                mMediaSessionToken = session;
                mExtras = extra;
                mState = CONNECT_STATE_CONNECTED;

                if (DBG) {
                    Log.d(TAG, "ServiceCallbacks.onConnect...");
                    dump();
                }
                mCallback.onConnected();

                // we may receive some subscriptions before we are connected, so re-subscribe
                // everything now
                for (Entry<String, Subscription> subscriptionEntry : mSubscriptions.entrySet()) {
                    String id = subscriptionEntry.getKey();
                    Subscription sub = subscriptionEntry.getValue();
                    List<SubscriptionCallback> callbackList = sub.getCallbacks();
                    List<Bundle> optionsList = sub.getOptionsList();
                    for (int i = 0; i < callbackList.size(); ++i) {
                        try {
                            mServiceBinder.addSubscription(id, callbackList.get(i).mToken,
                                    optionsList.get(i), mServiceCallbacks);
                        } catch (RemoteException ex) {
                            // Process is crashing. We will disconnect, and upon reconnect we will
                            // automatically reregister. So nothing to do here.
                            Log.d(TAG, "addSubscription failed with RemoteException parentId="
                                    + id);
                        }
                    }
                }
            }
        });
    }

    private final void onConnectionFailed(final IMediaBrowserServiceCallbacks callback) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                Log.e(TAG, "onConnectFailed for " + mServiceComponent);

                // Check to make sure there hasn't been a disconnect or a different
                // ServiceConnection.
                if (!isCurrent(callback, "onConnectFailed")) {
                    return;
                }
                // Don't allow them to call us twice.
                if (mState != CONNECT_STATE_CONNECTING) {
                    Log.w(TAG, "onConnect from service while mState="
                            + getStateLabel(mState) + "... ignoring");
                    return;
                }

                // Clean up
                forceCloseConnection();

                // Tell the app.
                mCallback.onConnectionFailed();
            }
        });
    }

    private final void onLoadChildren(final IMediaBrowserServiceCallbacks callback,
            final String parentId, final ParceledListSlice list, final Bundle options) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                // Check that there hasn't been a disconnect or a different
                // ServiceConnection.
                if (!isCurrent(callback, "onLoadChildren")) {
                    return;
                }

                if (DBG) {
                    Log.d(TAG, "onLoadChildren for " + mServiceComponent + " id=" + parentId);
                }

                // Check that the subscription is still subscribed.
                final Subscription subscription = mSubscriptions.get(parentId);
                if (subscription != null) {
                    // Tell the app.
                    SubscriptionCallback subscriptionCallback = subscription.getCallback(options);
                    if (subscriptionCallback != null) {
                        List<MediaItem> data = list == null ? null : list.getList();
                        if (options == null) {
                            if (data == null) {
                                subscriptionCallback.onError(parentId);
                            } else {
                                subscriptionCallback.onChildrenLoaded(parentId, data);
                            }
                        } else {
                            if (data == null) {
                                subscriptionCallback.onError(parentId, options);
                            } else {
                                subscriptionCallback.onChildrenLoaded(parentId, data, options);
                            }
                        }
                        return;
                    }
                }
                if (DBG) {
                    Log.d(TAG, "onLoadChildren for id that isn't subscribed id=" + parentId);
                }
            }
        });
    }

    /**
     * Return true if {@code callback} is the current ServiceCallbacks. Also logs if it's not.
     */
    private boolean isCurrent(IMediaBrowserServiceCallbacks callback, String funcName) {
        if (mServiceCallbacks != callback || mState == CONNECT_STATE_DISCONNECTING
                || mState == CONNECT_STATE_DISCONNECTED) {
            if (mState != CONNECT_STATE_DISCONNECTING && mState != CONNECT_STATE_DISCONNECTED) {
                Log.i(TAG, funcName + " for " + mServiceComponent + " with mServiceConnection="
                        + mServiceCallbacks + " this=" + this);
            }
            return false;
        }
        return true;
    }

    private ServiceCallbacks getNewServiceCallbacks() {
        return new ServiceCallbacks(this);
    }

    /**
     * Log internal state.
     * @hide
     */
    void dump() {
        Log.d(TAG, "MediaBrowser...");
        Log.d(TAG, "  mServiceComponent=" + mServiceComponent);
        Log.d(TAG, "  mCallback=" + mCallback);
        Log.d(TAG, "  mRootHints=" + mRootHints);
        Log.d(TAG, "  mState=" + getStateLabel(mState));
        Log.d(TAG, "  mServiceConnection=" + mServiceConnection);
        Log.d(TAG, "  mServiceBinder=" + mServiceBinder);
        Log.d(TAG, "  mServiceCallbacks=" + mServiceCallbacks);
        Log.d(TAG, "  mRootId=" + mRootId);
        Log.d(TAG, "  mMediaSessionToken=" + mMediaSessionToken);
    }

    /**
     * A class with information on a single media item for use in browsing/searching media.
     * MediaItems are application dependent so we cannot guarantee that they contain the
     * right values.
     */
    public static class MediaItem implements Parcelable {
        private final int mFlags;
        private final MediaDescription mDescription;

        /** @hide */
        @Retention(RetentionPolicy.SOURCE)
        @IntDef(flag=true, value = { FLAG_BROWSABLE, FLAG_PLAYABLE })
        public @interface Flags { }

        /**
         * Flag: Indicates that the item has children of its own.
         */
        public static final int FLAG_BROWSABLE = 1 << 0;

        /**
         * Flag: Indicates that the item is playable.
         * <p>
         * The id of this item may be passed to
         * {@link MediaController.TransportControls#playFromMediaId(String, Bundle)}
         * to start playing it.
         * </p>
         */
        public static final int FLAG_PLAYABLE = 1 << 1;

        /**
         * Create a new MediaItem for use in browsing media.
         * @param description The description of the media, which must include a
         *            media id.
         * @param flags The flags for this item.
         */
        public MediaItem(@NonNull MediaDescription description, @Flags int flags) {
            if (description == null) {
                throw new IllegalArgumentException("description cannot be null");
            }
            if (TextUtils.isEmpty(description.getMediaId())) {
                throw new IllegalArgumentException("description must have a non-empty media id");
            }
            mFlags = flags;
            mDescription = description;
        }

        /**
         * Private constructor.
         */
        private MediaItem(Parcel in) {
            mFlags = in.readInt();
            mDescription = MediaDescription.CREATOR.createFromParcel(in);
        }

        @Override
        public int describeContents() {
            return 0;
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            out.writeInt(mFlags);
            mDescription.writeToParcel(out, flags);
        }

        @Override
        public String toString() {
            final StringBuilder sb = new StringBuilder("MediaItem{");
            sb.append("mFlags=").append(mFlags);
            sb.append(", mDescription=").append(mDescription);
            sb.append('}');
            return sb.toString();
        }

        public static final Parcelable.Creator<MediaItem> CREATOR =
                new Parcelable.Creator<MediaItem>() {
                    @Override
                    public MediaItem createFromParcel(Parcel in) {
                        return new MediaItem(in);
                    }

                    @Override
                    public MediaItem[] newArray(int size) {
                        return new MediaItem[size];
                    }
                };

        /**
         * Gets the flags of the item.
         */
        public @Flags int getFlags() {
            return mFlags;
        }

        /**
         * Returns whether this item is browsable.
         * @see #FLAG_BROWSABLE
         */
        public boolean isBrowsable() {
            return (mFlags & FLAG_BROWSABLE) != 0;
        }

        /**
         * Returns whether this item is playable.
         * @see #FLAG_PLAYABLE
         */
        public boolean isPlayable() {
            return (mFlags & FLAG_PLAYABLE) != 0;
        }

        /**
         * Returns the description of the media.
         */
        public @NonNull MediaDescription getDescription() {
            return mDescription;
        }

        /**
         * Returns the media id in the {@link MediaDescription} for this item.
         * @see android.media.MediaMetadata#METADATA_KEY_MEDIA_ID
         */
        public @Nullable String getMediaId() {
            return mDescription.getMediaId();
        }
    }

    /**
     * Callbacks for connection related events.
     */
    public static class ConnectionCallback {
        /**
         * Invoked after {@link MediaBrowser#connect()} when the request has successfully completed.
         */
        public void onConnected() {
        }

        /**
         * Invoked when the client is disconnected from the media browser.
         */
        public void onConnectionSuspended() {
        }

        /**
         * Invoked when the connection to the media browser failed.
         */
        public void onConnectionFailed() {
        }
    }

    /**
     * Callbacks for subscription related events.
     */
    public static abstract class SubscriptionCallback {
        Binder mToken;

        public SubscriptionCallback() {
            mToken = new Binder();
        }

        /**
         * Called when the list of children is loaded or updated.
         *
         * @param parentId The media id of the parent media item.
         * @param children The children which were loaded.
         */
        public void onChildrenLoaded(@NonNull String parentId, @NonNull List<MediaItem> children) {
        }

        /**
         * Called when the list of children is loaded or updated.
         *
         * @param parentId The media id of the parent media item.
         * @param children The children which were loaded.
         * @param options The bundle of service-specific arguments sent to the media
         *            browser service. The contents of this bundle may affect the
         *            information returned when browsing.
         */
        public void onChildrenLoaded(@NonNull String parentId, @NonNull List<MediaItem> children,
                @NonNull Bundle options) {
        }

        /**
         * Called when the id doesn't exist or other errors in subscribing.
         * <p>
         * If this is called, the subscription remains until {@link MediaBrowser#unsubscribe}
         * called, because some errors may heal themselves.
         * </p>
         *
         * @param parentId The media id of the parent media item whose children could
         *            not be loaded.
         */
        public void onError(@NonNull String parentId) {
        }

        /**
         * Called when the id doesn't exist or other errors in subscribing.
         * <p>
         * If this is called, the subscription remains until {@link MediaBrowser#unsubscribe}
         * called, because some errors may heal themselves.
         * </p>
         *
         * @param parentId The media id of the parent media item whose children could
         *            not be loaded.
         * @param options The bundle of service-specific arguments sent to the media
         *            browser service.
         */
        public void onError(@NonNull String parentId, @NonNull Bundle options) {
        }
    }

    /**
     * Callback for receiving the result of {@link #getItem}.
     */
    public static abstract class ItemCallback {
        /**
         * Called when the item has been returned by the connected service.
         *
         * @param item The item that was returned or null if it doesn't exist.
         */
        public void onItemLoaded(MediaItem item) {
        }

        /**
         * Called there was an error retrieving it or the connected service doesn't support
         * {@link #getItem}.
         *
         * @param mediaId The media id of the media item which could not be loaded.
         */
        public void onError(@NonNull String mediaId) {
        }
    }

    /**
     * ServiceConnection to the other app.
     */
    private class MediaServiceConnection implements ServiceConnection {
        @Override
        public void onServiceConnected(final ComponentName name, final IBinder binder) {
            postOrRun(new Runnable() {
                @Override
                public void run() {
                    if (DBG) {
                        Log.d(TAG, "MediaServiceConnection.onServiceConnected name=" + name
                                + " binder=" + binder);
                        dump();
                    }

                    // Make sure we are still the current connection, and that they haven't called
                    // disconnect().
                    if (!isCurrent("onServiceConnected")) {
                        return;
                    }

                    // Save their binder
                    mServiceBinder = IMediaBrowserService.Stub.asInterface(binder);

                    // We make a new mServiceCallbacks each time we connect so that we can drop
                    // responses from previous connections.
                    mServiceCallbacks = getNewServiceCallbacks();
                    mState = CONNECT_STATE_CONNECTING;

                    // Call connect, which is async. When we get a response from that we will
                    // say that we're connected.
                    try {
                        if (DBG) {
                            Log.d(TAG, "ServiceCallbacks.onConnect...");
                            dump();
                        }
                        mServiceBinder.connect(mContext.getPackageName(), mRootHints,
                                mServiceCallbacks);
                    } catch (RemoteException ex) {
                        // Connect failed, which isn't good. But the auto-reconnect on the service
                        // will take over and we will come back. We will also get the
                        // onServiceDisconnected, which has all the cleanup code. So let that do
                        // it.
                        Log.w(TAG, "RemoteException during connect for " + mServiceComponent);
                        if (DBG) {
                            Log.d(TAG, "ServiceCallbacks.onConnect...");
                            dump();
                        }
                    }
                }
            });
        }

        @Override
        public void onServiceDisconnected(final ComponentName name) {
            postOrRun(new Runnable() {
                @Override
                public void run() {
                    if (DBG) {
                        Log.d(TAG, "MediaServiceConnection.onServiceDisconnected name=" + name
                                + " this=" + this + " mServiceConnection=" + mServiceConnection);
                        dump();
                    }

                    // Make sure we are still the current connection, and that they haven't called
                    // disconnect().
                    if (!isCurrent("onServiceDisconnected")) {
                        return;
                    }

                    // Clear out what we set in onServiceConnected
                    mServiceBinder = null;
                    mServiceCallbacks = null;

                    // And tell the app that it's suspended.
                    mState = CONNECT_STATE_SUSPENDED;
                    mCallback.onConnectionSuspended();
                }
            });
        }

        private void postOrRun(Runnable r) {
            if (Thread.currentThread() == mHandler.getLooper().getThread()) {
                r.run();
            } else {
                mHandler.post(r);
            }
        }

        /**
         * Return true if this is the current ServiceConnection. Also logs if it's not.
         */
        private boolean isCurrent(String funcName) {
            if (mServiceConnection != this || mState == CONNECT_STATE_DISCONNECTING
                    || mState == CONNECT_STATE_DISCONNECTED) {
                if (mState != CONNECT_STATE_DISCONNECTING && mState != CONNECT_STATE_DISCONNECTED) {
                    // Check mState, because otherwise this log is noisy.
                    Log.i(TAG, funcName + " for " + mServiceComponent + " with mServiceConnection="
                            + mServiceConnection + " this=" + this);
                }
                return false;
            }
            return true;
        }
    }

    /**
     * Callbacks from the service.
     */
    private static class ServiceCallbacks extends IMediaBrowserServiceCallbacks.Stub {
        private WeakReference<MediaBrowser> mMediaBrowser;

        public ServiceCallbacks(MediaBrowser mediaBrowser) {
            mMediaBrowser = new WeakReference<MediaBrowser>(mediaBrowser);
        }

        /**
         * The other side has acknowledged our connection. The parameters to this function
         * are the initial data as requested.
         */
        @Override
        public void onConnect(String root, MediaSession.Token session,
                final Bundle extras) {
            MediaBrowser mediaBrowser = mMediaBrowser.get();
            if (mediaBrowser != null) {
                mediaBrowser.onServiceConnected(this, root, session, extras);
            }
        }

        /**
         * The other side does not like us. Tell the app via onConnectionFailed.
         */
        @Override
        public void onConnectFailed() {
            MediaBrowser mediaBrowser = mMediaBrowser.get();
            if (mediaBrowser != null) {
                mediaBrowser.onConnectionFailed(this);
            }
        }

        @Override
        public void onLoadChildren(String parentId, ParceledListSlice list) {
            onLoadChildrenWithOptions(parentId, list, null);
        }

        @Override
        public void onLoadChildrenWithOptions(String parentId, ParceledListSlice list,
                final Bundle options) {
            MediaBrowser mediaBrowser = mMediaBrowser.get();
            if (mediaBrowser != null) {
                mediaBrowser.onLoadChildren(this, parentId, list, options);
            }
        }
    }

    private static class Subscription {
        private final List<SubscriptionCallback> mCallbacks;
        private final List<Bundle> mOptionsList;

        public Subscription() {
            mCallbacks = new ArrayList<>();
            mOptionsList = new ArrayList<>();
        }

        public boolean isEmpty() {
            return mCallbacks.isEmpty();
        }

        public List<Bundle> getOptionsList() {
            return mOptionsList;
        }

        public List<SubscriptionCallback> getCallbacks() {
            return mCallbacks;
        }

        public SubscriptionCallback getCallback(Bundle options) {
            for (int i = 0; i < mOptionsList.size(); ++i) {
                if (MediaBrowserUtils.areSameOptions(mOptionsList.get(i), options)) {
                    return mCallbacks.get(i);
                }
            }
            return null;
        }

        public void putCallback(Bundle options, SubscriptionCallback callback) {
            for (int i = 0; i < mOptionsList.size(); ++i) {
                if (MediaBrowserUtils.areSameOptions(mOptionsList.get(i), options)) {
                    mCallbacks.set(i, callback);
                    return;
                }
            }
            mCallbacks.add(callback);
            mOptionsList.add(options);
        }
    }
}