1、主Activity的 code。
对按钮绑定事件,并在触发后发送Intent意图给service。之所以用setcontent的 方法。是因为这样的话,可以知道信息来源的类名、包名
package com.example.mediaplaer4musicbyservice; import android.app.Activity; import android.content.ComponentName; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.view.View.OnClickListener; public class MediaPlaer4MusicByService extends Activity implements OnClickListener{ private Button mPrevious,mPlay,mNext,mPause; private ComponentName component; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); //oncreate里代码一如既往的少 setupViews(); } //初始化一些工作 public void setupViews(){ component = new ComponentName(this, MusicService.class); mPrevious = (Button)findViewById(R.id.previous); mPlay = (Button)findViewById(R.id.play); mNext = (Button)findViewById(R.id.next); mPause = (Button)findViewById(R.id.pause); mPrevious.setOnClickListener(this); mPlay.setOnClickListener(this); mNext.setOnClickListener(this); mPause.setOnClickListener(this); } //按钮点击事件响应 public void onClick(View v) { if(v == mPrevious){ Intent mIntent = new Intent(MusicService.PREVIOUS_ACTION); mIntent.setComponent(component); startService(mIntent); }else if(v == mPlay){ Intent mIntent = new Intent(MusicService.PLAY_ACTION); mIntent.setComponent(component); startService(mIntent); }else if(v == mNext){ Intent mIntent = new Intent(MusicService.NEXT_ACTION); mIntent.setComponent(component); startService(mIntent); }else{ Intent mIntent = new Intent(MusicService.PAUSE_ACTION); mIntent.setComponent(component); startService(mIntent); } } }
2、MusicService.java
package com.example.mediaplaer4musicbyservice; import java.io.IOException; import android.app.Service; import android.content.Intent; import android.database.Cursor; import android.media.MediaPlayer; import android.net.Uri; import android.os.IBinder; import android.provider.MediaStore; import android.widget.Toast; public class MusicService extends Service { String[] mCursorCols = new String[] { "audio._id AS _id", // index must match IDCOLIDX below MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.ALBUM, MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.DATA, MediaStore.Audio.Media.MIME_TYPE, MediaStore.Audio.Media.ALBUM_ID, MediaStore.Audio.Media.ARTIST_ID, MediaStore.Audio.Media.DURATION }; private MediaPlayer mMediaPlayer; private Cursor mCursor; private int mPlayPosition = 0; public static final String PLAY_ACTION = "com.tutor.music.PLAY_ACTION"; public static final String PAUSE_ACTION = "com.tutor.music.PAUSE_ACTION"; public static final String NEXT_ACTION = "com.tutor.music.NEXT_ACTION"; public static final String PREVIOUS_ACTION = "com.tutor.music.PREVIOUS_ACTION"; @Override public IBinder onBind(Intent arg0) { // TODO Auto-generated method stub return null; } @Override public void onCreate() { super.onCreate(); mMediaPlayer = new MediaPlayer(); //通过一个URI可以获取所有音频文件 Uri MUSIC_URL = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI; //这里我过滤了一下,因为我机里有些音频文件是游戏音频,很短 //播放不到一秒钟,我这里作了处理,默认大于10秒的可以看作是歌 mCursor = getContentResolver().query(MUSIC_URL, mCursorCols, "duration > 10000", null, null); } @Override public void onStart(Intent intent, int startId) { super.onStart(intent, startId); String action = intent.getAction(); if(action.equals(PLAY_ACTION)){ play(); }else if(action.equals(PAUSE_ACTION)){ pause(); }else if(action.equals(NEXT_ACTION)){ next(); }else if(action.equals(PREVIOUS_ACTION)){ previous(); } } //play the music public void play() { inite(); } //暂停时,结束服务 public void pause() { stopSelf(); } //上一首 public void previous() { if (mPlayPosition == 0) { mPlayPosition = mCursor.getCount() - 1; } else { mPlayPosition--; } inite(); } public void next() { if (mPlayPosition == mCursor.getCount() - 1) { mPlayPosition = 0; } else { mPlayPosition++; } inite(); } public void inite() { mMediaPlayer.reset(); String dataSource = getDateByPosition(mCursor, mPlayPosition); String info = getInfoByPosition(mCursor, mPlayPosition); //用Toast显示歌曲信息 Toast.makeText(getApplicationContext(), info, Toast.LENGTH_SHORT).show(); try { mMediaPlayer.setDataSource(dataSource); mMediaPlayer.prepare(); mMediaPlayer.start(); } catch (IllegalArgumentException e1) { e1.printStackTrace(); } catch (IllegalStateException e1) { e1.printStackTrace(); } catch (IOException e1) { e1.printStackTrace(); } } //根据位置来获取歌曲位置 public String getDateByPosition(Cursor c,int position){ c.moveToPosition(position); int dataColumn = c.getColumnIndex(MediaStore.Audio.Media.DATA); String data = c.getString(dataColumn); return data; } //获取当前播放歌曲演唱者及歌名 public String getInfoByPosition(Cursor c,int position){ c.moveToPosition(position); int titleColumn = c.getColumnIndex(MediaStore.Audio.Media.TITLE); int artistColumn = c.getColumnIndex(MediaStore.Audio.Media.ARTIST); String info = c.getString(artistColumn)+" " + c.getString(titleColumn); return info; } //服务结束时要释放MediaPlayer public void onDestroy() { super.onDestroy(); mMediaPlayer.release(); } }
(1)mCursorCols是定义准备用来数据查询的字段
(2)是注册意图的意思:
<span style="white-space:pre"> </span>public static final String PLAY_ACTION = "com.tutor.music.PLAY_ACTION"; public static final String PAUSE_ACTION = "com.tutor.music.PAUSE_ACTION"; public static final String NEXT_ACTION = "com.tutor.music.NEXT_ACTION"; public static final String PREVIOUS_ACTION = "com.tutor.music.PREVIOUS_ACTION";
(3)
这是contentProvider标志音乐的uri
Uri MUSIC_URL = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;(4)service在主Activity 调用startService之后的工作流程是怎样的呢?这涉及到service的生命周期
首先startService(),service就会启动oncreate(),onStart()。这样启动的service会一直在后台进行,直到调用了Context.stopService()或者stopSelf()方法。
如果一个service已经启动,在别的地方再次启动该service的时候,此时不再onCreate不再执行,而是从onStart()开始执行。
(5)另外下面的
<span style="white-space:pre"> </span>public IBinder onBind(Intent arg0) { // TODO Auto-generated method stub return null; }什么意思呢?这涉及到service的 另一种生命周期。把这个service和调用service的客户类绑定起来,如果客户类销毁了,该service也会被销毁。
bindService()执行之后,service会执行上面的方法onBind(),你可以从这里返回一个实现Ibind接口的类,在客户端操作这个类就能和service通信了。
如果service还没有运行 ,使用这个方法启动service就会执行onCreate而不执行onStart()方法
(6)
mCursor = getContentResolver().query(MUSIC_URL, mCursorCols, "duration > 10000", null, null);
getContentResolver().query这个方法的第一个参数是uri,第二个参数是要查询的列的字段,第三个是筛选条件,第四个替代第三个?部分,第五个是排序顺序
详情见:点击打开链接
(7)注册的意图是为了知道调用service的主人需要service做什么
(8)cursor类的
getColumnIndex返回指定列的index