AN开发范例实战宝典学习日记一:使用Service 、contentProvider编写的音乐播放器


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


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