本文开发一个基于Service的音乐播放器，音乐由后台运行的Service负责播放，当后台的播放状态发生变化时，程序将会通过发送广播通知前台Activity更新界面；当点击Activity的界面按钮时，系统将通过发送广播通知后台Service来改变播放状态。
前台Activity界面有两个按钮，分别用于控制播放/暂停、停止，另外还有两个文本框，用于显示正在播放的歌曲名、歌手名。前台Activity的代码如下：
public class MainActivity extends AppCompatActivity implements View.OnClickListener{
private ImageButton mStart;
private ImageButton mStop;
private TextView mMusicName;
private TextView mSongerName;
private ActivityReceiver mActivityReceiver;
public static final String CTL_ACTION = "com.trampcr.action.CTL_ACTION";
public static final String UPDATE_ACTION = "com.trampcr.action.UPDATE_ACTION";
//定义音乐播放状态，0x11代表没有播放，0x12代表正在播放，0x13代表暂停
int status = 0x11;
String[] musicNames = new String[]{"完美生活", "那一年", "故乡"};
String[] songerNames = new String[]{"许巍", "许巍", "许巍"};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mStart = (ImageButton) findViewById(R.id.start);
mStop = (ImageButton) findViewById(R.id.stop);
mMusicName = (TextView) findViewById(R.id.music_name);
mSongerName = (TextView) findViewById(R.id.songer_name);
mStart.setOnClickListener(this);
mStop.setOnClickListener(this);
mActivityReceiver = new ActivityReceiver();
//创建IntentFilter
IntentFilter filter = new IntentFilter();
//指定BroadcastReceiver监听的Action
filter.addAction(UPDATE_ACTION);
//注册BroadcastReceiver
registerReceiver(mActivityReceiver, filter);
Intent intent = new Intent(MainActivity.this, MusicService.class);
//启动后台Service
startService(intent);
}
public class ActivityReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
//获取Intent中的update消息，update代表播放状态
int update = intent.getIntExtra("update", -1);
//获取Intent中的current消息，current代表当前正在播放的歌曲
int current = intent.getIntExtra("current", -1);
if (current >= 0){
mMusicName.setText(musicNames[current]);
mSongerName.setText(songerNames[current]);
}
switch (update){
case 0x11:
mStart.setBackgroundResource(R.drawable.play);
status = 0x11;
break;
//控制系统进入播放状态
case 0x12:
//在播放状态下设置使用暂停图标
mStart.setBackgroundResource(R.drawable.pause);
status = 0x12;
break;
case 0x13:
//在暂停状态下设置使用播放图标
mStart.setBackgroundResource(R.drawable.play);
status = 0x13;
break;
}
}
}
@Override
public void onClick(View v) {
Intent intent = new Intent(CTL_ACTION);
switch (v.getId()){
case R.id.start:
intent.putExtra("control", 1);
break;
case R.id.stop:
intent.putExtra("control", 2);
break;
}
//发送广播，将被Service中的BroadcastReceiver接收到
sendBroadcast(intent);
}
}
ActivityReceiver()用于响应后台Service所发出的广播，该程序将会根据广播Intent里的消息来改变播放状态，并更新程序界面中按钮的图标。
onClick中根据点击的按钮发送广播，发送广播时会把所按下的按钮标识发送出来。
接下来是后台Service，会在播放状态发生改变时对外发送广播。代码如下：
public class MusicService extends Service {
MyReceiver serviceReceiver;
AssetManager mAssetManager;
String[] musics = new String[]{"prefectLife.mp3", "thatYear.mp3", "country.mp3"};
MediaPlayer mMediaPlayer;
int status = 0x11;
int current = 0; // 记录当前正在播放的音乐
@Nullable
@Override
public IBinder onBind(Intent intent) {
return null;
}
@Override
public void onCreate() {
super.onCreate();
mAssetManager = getAssets();
serviceReceiver = new MyReceiver();
//创建IntentFilter
IntentFilter filter = new IntentFilter();
filter.addAction(MainActivity.CTL_ACTION);
registerReceiver(serviceReceiver, filter);
//创建MediaPlayer
mMediaPlayer = new MediaPlayer();
//为MediaPlayer播放完成事件绑定监听器
mMediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
@Override
public void onCompletion(MediaPlayer mp) {
current++;
if (current >= 3) {
current = 0;
}
//发送广播通知Activity更改文本框
Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);
sendIntent.putExtra("current", current);
//发送广播，将被Activity中的BroadcastReceiver接收到
sendBroadcast(sendIntent);
//准备并播放音乐
prepareAndPlay(musics[current]);
}
});
}
public class MyReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
int control = intent.getIntExtra("control", -1);
switch (control){
case 1: // 播放或暂停
//原来处于没有播放状态
if (status ==0x11){
//准备播放音乐
prepareAndPlay(musics[current]);
status = 0x12;
}
//原来处于播放状态
else if (status == 0x12){
//暂停
mMediaPlayer.pause();
status = 0x13; // 改变为暂停状态
}
//原来处于暂停状态
else if (status == 0x13){
//播放
mMediaPlayer.start();
status = 0x12; // 改变状态
}
break;
//停止声音
case 2:
//如果原来正在播放或暂停
if (status == 0x12 || status == 0x13){
//停止播放
mMediaPlayer.stop();
status = 0x11;
}
}
//广播通知Activity更改图标、文本框
Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);
sendIntent.putExtra("update", status);
sendIntent.putExtra("current", current);
//发送广播，将被Activity中的BroadcastReceiver接收到
sendBroadcast(sendIntent);
}
}
private void prepareAndPlay(String music) {
try {
//打开指定的音乐文件
AssetFileDescriptor assetFileDescriptor = mAssetManager.openFd(music);
mMediaPlayer.reset();
//使用MediaPlayer加载指定的声音文件
mMediaPlayer.setDataSource(assetFileDescriptor.getFileDescriptor(), assetFileDescriptor.getStartOffset(), assetFileDescriptor.getLength());
mMediaPlayer.prepare(); // 准备声音
mMediaPlayer.start(); // 播放
} catch (IOException e) {
e.printStackTrace();
}
}
}
MyReceiver用于接收前台Activity所发出的广播，并根据广播的消息内容改变Service的播放状态，当播放状态改变时，该Service对外发送一条广播，广播消息将会被前台Activity接收，前台Activity将会根据广播消息更新界面。
为了让该音乐播放器能按顺序依次播放歌曲，程序为MediaPlayer增加了OnCompletionListener监听器，当MediaPlayer播放完成后将自动播放下一首歌曲。
运行程序，效果图如下：
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。
