The file containing the source code shown below is located in the corresponding directory in <sdk>/samples/android-<version>/...
/*
* Copyright (C) 2011 The Android开源工程
*
* 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.example.android.musicplayer;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.media.AudioManager;
import android.media.MediaMetadataRetriever;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.media.MediaPlayer.OnErrorListener;
import android.media.MediaPlayer.OnPreparedListener;
import android.media.RemoteControlClient;
import android.net.Uri;
import android.net.wifi.WifiManager;
import android.net.wifi.WifiManager.WifiLock;
import android.os.IBinder;
import android.os.PowerManager;
import android.util.Log;
import android.widget.Toast;
import java.io.IOException;
/**
* Service that handles media playback. This is the Service through which we perform all the media
* handling in our application. Upon initialization, it starts a {@link MusicRetriever} to scan
* the user's media. Then, it waits for Intents (which come from our main activity,
* {@link MainActivity}, which signal the service to perform specific operations: Play, Pause,
* Rewind, Skip, etc.
*/
public class MusicService extends Service implements OnCompletionListener, OnPreparedListener,
OnErrorListener, MusicFocusable,
PrepareMusicRetrieverTask.MusicRetrieverPreparedListener {
// The tag we put on debug messages
final static String TAG = "RandomMusicPlayer";
// These are the Intent actions that we are prepared to handle. Notice that the fact these
// constants exist in our class is a mere convenience: what really defines the actions our
// service can handle are the <action> tags in the <intent-filters> tag for our service in
// AndroidManifest.xml.
public static final String ACTION_TOGGLE_PLAYBACK =
"com.example.android.musicplayer.action.TOGGLE_PLAYBACK";
public static final String ACTION_PLAY = "com.example.android.musicplayer.action.PLAY";
public static final String ACTION_PAUSE = "com.example.android.musicplayer.action.PAUSE";
public static final String ACTION_STOP = "com.example.android.musicplayer.action.STOP";
public static final String ACTION_SKIP = "com.example.android.musicplayer.action.SKIP";
public static final String ACTION_REWIND = "com.example.android.musicplayer.action.REWIND";
public static final String ACTION_URL = "com.example.android.musicplayer.action.URL";
// The volume we set the media player to when we lose audio focus, but are allowed to reduce
// the volume instead of stopping playback.
public static final float DUCK_VOLUME = 0.1f;
// our media player
MediaPlayer mPlayer = null;
// our AudioFocusHelper object, if it's available (it's available on SDK level >= 8)
// If not available, this will be null. Always check for null before using!
AudioFocusHelper mAudioFocusHelper = null;
// indicates the state our service:
enum State {
Retrieving, // the MediaRetriever is retrieving music
Stopped, // media player is stopped and not prepared to play
Preparing, // media player is preparing...
Playing, // playback active (media player ready!). (but the media player may actually be
// paused in this state if we don't have audio focus. But we stay in this state
// so that we know we have to resume playback once we get focus back)
Paused // playback paused (media player ready!)
};
State mState = State.Retrieving;
// if in Retrieving mode, this flag indicates whether we should start playing immediately
// when we are ready or not.
boolean mStartPlayingAfterRetrieve = false;
// if mStartPlayingAfterRetrieve is true, this variable indicates the URL that we should
// start playing when we are ready. If null, we should play a random song from the device
Uri mWhatToPlayAfterRetrieve = null;
enum PauseReason {
UserRequest, // paused by user request
FocusLoss, // paused because of audio focus loss
};
// why did we pause? (only relevant if mState == State.Paused)
PauseReason mPauseReason = PauseReason.UserRequest;
// do we have audio focus?
enum AudioFocus {
NoFocusNoDuck, // we don't have audio focus, and can't duck
NoFocusCanDuck, // we don't have focus, but can play at a low volume ("ducking")
Focused // we have full audio focus
}
AudioFocus mAudioFocus = AudioFocus.NoFocusNoDuck;
// title of the song we are currently playing
String mSongTitle = "";
// whether the song we are playing is streaming from the network
boolean mIsStreaming = false;
// Wifi lock that we hold when streaming files from the internet, in order to prevent the
// device from shutting off the Wifi radio
WifiLock mWifiLock;
// The ID we use for the notification (the onscreen alert that appears at the notification
// area at the top of the screen as an icon -- and as text as well if the user expands the
// notification area).
final int NOTIFICATION_ID = 1;
// Our instance of our MusicRetriever, which handles scanning for media and
// providing titles and URIs as we need.
MusicRetriever mRetriever;
// our RemoteControlClient object, which will use remote control APIs available in
// SDK level >= 14, if they're available.
RemoteControlClientCompat mRemoteControlClientCompat;
// Dummy album art we will pass to the remote control (if the APIs are available).
Bitmap mDummyAlbumArt;
// The component name of MusicIntentReceiver, for use with media button and remote control
// APIs
ComponentName mMediaButtonReceiverComponent;
AudioManager mAudioManager;
NotificationManager mNotificationManager;
Notification mNotification = null;
/**
* Makes sure the media player exists and has been reset. This will create the media player
* if needed, or reset the existing media player if one already exists.
*/
void createMediaPlayerIfNeeded() {
if (mPlayer == null) {
mPlayer = new MediaPlayer();
// Make sure the media player will acquire a wake-lock while playing. If we don't do
// that, the CPU might go to sleep while the song is playing, causing playback to stop.
//
// Remember that to use this, we have to declare the android.permission.WAKE_LOCK
// permission in AndroidManifest.xml.
mPlayer.setWakeMode(getApplicationContext(), PowerManager.PARTIAL_WAKE_LOCK);
// we want the media player to notify us when it's ready preparing, and when it's done
// playing:
mPlayer.setOnPreparedListener(this);
mPlayer.setOnCompletionListener(this);
mPlayer.setOnErrorListener(this);
}
else
mPlayer.reset();
}
@Override
public void onCreate() {
Log.i(TAG, "debug: Creating service");
// Create the Wifi lock (this does not acquire the lock, this just creates it)
mWifiLock = ((WifiManager) getSystemService(Context.WIFI_SERVICE))
.createWifiLock(WifiManager.WIFI_MODE_FULL, "mylock");
mNotificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
mAudioManager = (AudioManager) getSystemService(AUDIO_SERVICE);
// Create the retriever and start an asynchronous task that will prepare it.
mRetriever = new MusicRetriever(getContentResolver());
(new PrepareMusicRetrieverTask(mRetriever,this)).execute();
// create the Audio Focus Helper, if the Audio Focus feature is available (SDK 8 or above)
if (android.os.Build.VERSION.SDK_INT >= 8)
mAudioFocusHelper = new AudioFocusHelper(getApplicationContext(), this);
else
mAudioFocus = AudioFocus.Focused; // no focus feature, so we always "have" audio focus
mDummyAlbumArt = BitmapFactory.decodeResource(getResources(), R.drawable.dummy_album_art);
mMediaButtonReceiverComponent = new ComponentName(this, MusicIntentReceiver.class);
}
/**
* Called when we receive an Intent. When we receive an intent sent to us via startService(),
* this is the method that gets called. So here we react appropriately depending on the
* Intent's action, which specifies what is being requested of us.
*/
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
String action = intent.getAction();
if (action.equals(ACTION_TOGGLE_PLAYBACK)) processTogglePlaybackRequest();
else if (action.equals(ACTION_PLAY)) processPlayRequest();
else if (action.equals(ACTION_PAUSE)) processPauseRequest();
else if (action.equals(ACTION_SKIP)) processSkipRequest();
else if (action.equals(ACTION_STOP)) processStopRequest();
else if (action.equals(ACTION_REWIND)) processRewindRequest();
else if (action.equals(ACTION_URL)) processAddRequest(intent);
return START_NOT_STICKY; // Means we started the service, but don't want it to
// restart in case it's killed.
}
void processTogglePlaybackRequest() {
if (mState == State.Paused || mState == State.Stopped) {
processPlayRequest();
} else {
processPauseRequest();
}
}
void processPlayRequest() {
if (mState == State.Retrieving) {
// If we are still retrieving media, just set the flag to start playing when we're
// ready
mWhatToPlayAfterRetrieve = null; // play a random song
mStartPlayingAfterRetrieve = true;
return;
}
tryToGetAudioFocus();
// actually play the song
if (mState == State.Stopped) {
// If we're stopped, just go ahead to the next song and start playing
playNextSong(null);
}
else if (mState == State.Paused) {
// If we're paused, just continue playback and restore the 'foreground service' state.
mState = State.Playing;
setUpAsForeground(mSongTitle + " (playing)");
configAndStartMediaPlayer();
}
// Tell any remote controls that our playback state is 'playing'.
if (mRemoteControlClientCompat != null) {
mRemoteControlClientCompat
.setPlaybackState(RemoteControlClient.PLAYSTATE_PLAYING);
}
}
void processPauseRequest() {
if (mState == State.Retrieving) {
// If we are still retrieving media, clear the flag that indicates we should start
// playing when we're ready
mStartPlayingAfterRetrieve = false;
return;
}
if (mState == State.Playing) {
// Pause media player and cancel the 'foreground service' state.
mState = State.Paused;
mPlayer.pause();
relaxResources(false); // while paused, we always retain the MediaPlayer
// do not give up audio focus
}
// Tell any remote controls that our playback state is 'paused'.
if (mRemoteControlClientCompat != null) {
mRemoteControlClientCompat
.setPlaybackState(RemoteControlClient.PLAYSTATE_PAUSED);
}
}
void processRewindRequest() {
if (mState == State.Playing || mState == State.Paused)
mPlayer.seekTo(0);
}
void processSkipRequest() {
if (mState == State.Playing || mState == State.Paused) {
tryToGetAudioFocus();
playNextSong(null);
}
}
void processStopRequest() {
processStopRequest(false);
}
void processStopRequest(boolean force) {
if (mState == State.Playing || mState == State.Paused || force) {
mState = State.Stopped;
// let go of all resources...
relaxResources(true);
giveUpAudioFocus();
// Tell any remote controls that our playback state is 'paused'.
if (mRemoteControlClientCompat != null) {
mRemoteControlClientCompat
.setPlaybackState(RemoteControlClient.PLAYSTATE_STOPPED);
}
// service is no longer necessary. Will be started again if needed.
stopSelf();
}
}
/**
* Releases resources used by the service for playback. This includes the "foreground service"
* status and notification, the wake locks and possibly the MediaPlayer.
*
* @param releaseMediaPlayer Indicates whether the Media Player should also be released or not
*/
void relaxResources(boolean releaseMediaPlayer) {
// stop being a foreground service
stopForeground(true);
// stop and release the Media Player, if it's available
if (releaseMediaPlayer && mPlayer != null) {
mPlayer.reset();
mPlayer.release();
mPlayer = null;
}
// we can also release the Wifi lock, if we're holding it
if (mWifiLock.isHeld()) mWifiLock.release();
}
void giveUpAudioFocus() {
if (mAudioFocus == AudioFocus.Focused && mAudioFocusHelper != null
&& mAudioFocusHelper.abandonFocus())
mAudioFocus = AudioFocus.NoFocusNoDuck;
}
/**
* Reconfigures MediaPlayer according to audio focus settings and starts/restarts it. This
* method starts/restarts the MediaPlayer respecting the current audio focus state. So if
* we have focus, it will play normally; if we don't have focus, it will either leave the
* MediaPlayer paused or set it to a low volume, depending on what is allowed by the
* current focus settings. This method assumes mPlayer != null, so if you are calling it,
* you have to do so from a context where you are sure this is the case.
*/
void configAndStartMediaPlayer() {
if (mAudioFocus == AudioFocus.NoFocusNoDuck) {
// If we don't have audio focus and can't duck, we have to pause, even if mState
// is State.Playing. But we stay in the Playing state so that we know we have to resume
// playback once we get the focus back.
if (mPlayer.isPlaying()) mPlayer.pause();
return;
}
else if (mAudioFocus == AudioFocus.NoFocusCanDuck)
mPlayer.setVolume(DUCK_VOLUME, DUCK_VOLUME); // we'll be relatively quiet
else
mPlayer.setVolume(1.0f, 1.0f); // we can be loud
if (!mPlayer.isPlaying()) mPlayer.start();
}
void processAddRequest(Intent intent) {
// user wants to play a song directly by URL or path. The URL or path comes in the "data"
// part of the Intent. This Intent is sent by {@link MainActivity} after the user
// specifies the URL/path via an alert box.
if (mState == State.Retrieving) {
// we'll play the requested URL right after we finish retrieving
mWhatToPlayAfterRetrieve = intent.getData();
mStartPlayingAfterRetrieve = true;
}
else if (mState == State.Playing || mState == State.Paused || mState == State.Stopped) {
Log.i(TAG, "Playing from URL/path: " + intent.getData().toString());
tryToGetAudioFocus();
playNextSong(intent.getData().toString());
}
}
void tryToGetAudioFocus() {
if (mAudioFocus != AudioFocus.Focused && mAudioFocusHelper != null
&& mAudioFocusHelper.requestFocus())
mAudioFocus = AudioFocus.Focused;
}
/**
* Starts playing the next song. If manualUrl is null, the next song will be randomly selected
* from our Media Retriever (that is, it will be a random song in the user's device). If
* manualUrl is non-null, then it specifies the URL or path to the song that will be played
* next.
*/
void playNextSong(String manualUrl) {
mState = State.Stopped;
relaxResources(false); // release everything except MediaPlayer
try {
MusicRetriever.Item playingItem = null;
if (manualUrl != null) {
// set the source of the media player to a manual URL or path
createMediaPlayerIfNeeded();
mPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
mPlayer.setDataSource(manualUrl);
mIsStreaming = manualUrl.startsWith("http:") || manualUrl.startsWith("https:");
playingItem = new MusicRetriever.Item(0, null, manualUrl, null, 0);
}
else {
mIsStreaming = false; // playing a locally available song
playingItem = mRetriever.getRandomItem();
if (playingItem == null) {
Toast.makeText(this,
"No available music to play. Place some music on your external storage "
+ "device (e.g. your SD card) and try again.",
Toast.LENGTH_LONG).show();
processStopRequest(true); // stop everything!
return;
}
// set the source of the media player a a content URI
createMediaPlayerIfNeeded();
mPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
mPlayer.setDataSource(getApplicationContext(), playingItem.getURI());
}
mSongTitle = playingItem.getTitle();
mState = State.Preparing;
setUpAsForeground(mSongTitle + " (loading)");
// Use the media button APIs (if available) to register ourselves for media button
// events
MediaButtonHelper.registerMediaButtonEventReceiverCompat(
mAudioManager, mMediaButtonReceiverComponent);
// Use the remote control APIs (if available) to set the playback state
if (mRemoteControlClientCompat == null) {
Intent intent = new Intent(Intent.ACTION_MEDIA_BUTTON);
intent.setComponent(mMediaButtonReceiverComponent);
mRemoteControlClientCompat = new RemoteControlClientCompat(
PendingIntent.getBroadcast(this /*context*/,
0 /*requestCode, ignored*/, intent /*intent*/, 0 /*flags*/));
RemoteControlHelper.registerRemoteControlClient(mAudioManager,
mRemoteControlClientCompat);
}
mRemoteControlClientCompat.setPlaybackState(
RemoteControlClient.PLAYSTATE_PLAYING);
mRemoteControlClientCompat.setTransportControlFlags(
RemoteControlClient.FLAG_KEY_MEDIA_PLAY |
RemoteControlClient.FLAG_KEY_MEDIA_PAUSE |
RemoteControlClient.FLAG_KEY_MEDIA_NEXT |
RemoteControlClient.FLAG_KEY_MEDIA_STOP);
// Update the remote controls
mRemoteControlClientCompat.editMetadata(true)
.putString(MediaMetadataRetriever.METADATA_KEY_ARTIST, playingItem.getArtist())
.putString(MediaMetadataRetriever.METADATA_KEY_ALBUM, playingItem.getAlbum())
.putString(MediaMetadataRetriever.METADATA_KEY_TITLE, playingItem.getTitle())
.putLong(MediaMetadataRetriever.METADATA_KEY_DURATION,
playingItem.getDuration())
// TODO: fetch real item artwork
.putBitmap(
RemoteControlClientCompat.MetadataEditorCompat.METADATA_KEY_ARTWORK,
mDummyAlbumArt)
.apply();
// starts preparing the media player in the background. When it's done, it will call
// our OnPreparedListener (that is, the onPrepared() method on this class, since we set
// the listener to 'this').
//
// Until the media player is prepared, we *cannot* call start() on it!
mPlayer.prepareAsync();
// If we are streaming from the internet, we want to hold a Wifi lock, which prevents
// the Wifi radio from going to sleep while the song is playing. If, on the other hand,
// we are *not* streaming, we want to release the lock if we were holding it before.
if (mIsStreaming) mWifiLock.acquire();
else if (mWifiLock.isHeld()) mWifiLock.release();
}
catch (IOException ex) {
Log.e("MusicService", "IOException playing next song: " + ex.getMessage());
ex.printStackTrace();
}
}
/** Called when media player is done playing current song. */
public void onCompletion(MediaPlayer player) {
// The media player finished playing the current song, so we go ahead and start the next.
playNextSong(null);
}
/** Called when media player is done preparing. */
public void onPrepared(MediaPlayer player) {
// The media player is done preparing. That means we can start playing!
mState = State.Playing;
updateNotification(mSongTitle + " (playing)");
configAndStartMediaPlayer();
}
/** Updates the notification. */
void updateNotification(String text) {
PendingIntent pi = PendingIntent.getActivity(getApplicationContext(), 0,
new Intent(getApplicationContext(), MainActivity.class),
PendingIntent.FLAG_UPDATE_CURRENT);
mNotification.setLatestEventInfo(getApplicationContext(), "RandomMusicPlayer", text, pi);
mNotificationManager.notify(NOTIFICATION_ID, mNotification);
}
/**
* Configures service as a foreground service. A foreground service is a service that's doing
* something the user is actively aware of (such as playing music), and must appear to the
* user as a notification. That's why we create the notification here.
*/
void setUpAsForeground(String text) {
PendingIntent pi = PendingIntent.getActivity(getApplicationContext(), 0,
new Intent(getApplicationContext(), MainActivity.class),
PendingIntent.FLAG_UPDATE_CURRENT);
mNotification = new Notification();
mNotification.tickerText = text;
mNotification.icon = R.drawable.ic_stat_playing;
mNotification.flags |= Notification.FLAG_ONGOING_EVENT;
mNotification.setLatestEventInfo(getApplicationContext(), "RandomMusicPlayer",
text, pi);
startForeground(NOTIFICATION_ID, mNotification);
}
/**
* Called when there's an error playing media. When this happens, the media player goes to
* the Error state. We warn the user about the error and reset the media player.
*/
public boolean onError(MediaPlayer mp, int what, int extra) {
Toast.makeText(getApplicationContext(), "Media player error! Resetting.",
Toast.LENGTH_SHORT).show();
Log.e(TAG, "Error: what=" + String.valueOf(what) + ", extra=" + String.valueOf(extra));
mState = State.Stopped;
relaxResources(true);
giveUpAudioFocus();
return true; // true indicates we handled the error
}
public void onGainedAudioFocus() {
Toast.makeText(getApplicationContext(), "gained audio focus.", Toast.LENGTH_SHORT).show();
mAudioFocus = AudioFocus.Focused;
// restart media player with new focus settings
if (mState == State.Playing)
configAndStartMediaPlayer();
}
public void onLostAudioFocus(boolean canDuck) {
Toast.makeText(getApplicationContext(), "lost audio focus." + (canDuck ? "can duck" :
"no duck"), Toast.LENGTH_SHORT).show();
mAudioFocus = canDuck ? AudioFocus.NoFocusCanDuck : AudioFocus.NoFocusNoDuck;
// start/restart/pause media player with new focus settings
if (mPlayer != null && mPlayer.isPlaying())
configAndStartMediaPlayer();
}
public void onMusicRetrieverPrepared() {
// Done retrieving!
mState = State.Stopped;
// If the flag indicates we should start playing after retrieving, let's do that now.
if (mStartPlayingAfterRetrieve) {
tryToGetAudioFocus();
playNextSong(mWhatToPlayAfterRetrieve == null ?
null : mWhatToPlayAfterRetrieve.toString());
}
}
@Override
public void onDestroy() {
// Service is being killed, so make sure we release our resources
mState = State.Stopped;
relaxResources(true);
giveUpAudioFocus();
}
@Override
public IBinder onBind(Intent arg0) {
return null;
}
}