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。