安卓系统媒体库

   Android系统的媒体文件管理方式：
     扫描存储设备上的公有媒体文件，并使用SQLite数据库记录下相关的信息：
        一般情况下，系统开机时会发出媒体扫描的广播，通知扫描程序进行扫描；
开发者开发的应用程序也可以调用扫描器实时扫描；
扫描到的媒体除了会在数据库中记录媒体文件的路径意外，还会记录下其他的相关信息，例如入库的时间、修改时间、图片详情、歌曲时长等；
            Android系统使用的ContentProvider以使得设备上的其他应用程序可以随时访问这些媒体数据。
   访问媒体库：系统中包名为com.android.providers.media的应用程序提供了媒体库的ContentProvider；
如何访问媒体库中的图片信息

             方法：

public class MainActivity extends Activity {
    @Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		ContentResolver cr = getContentResolver();
		Uri uri = Media.EXTERNAL_CONTENT_URI;
		Cursor cursor  = cr.query(uri, null, null, null, null);
		for(cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()){
			String path,display;
			long date;
			int size,width,height;
			path = cursor.getString(cursor.getColumnIndex(Media.DATA));
			display = cursor.getString(cursor.getColumnIndex(Media.DISPLAY_NAME));
			date = cursor.getLong(cursor.getColumnIndex(Media.DATE_TAKEN));
			size = cursor.getInt(cursor.getColumnIndex(Media.SIZE));
			width = cursor.getInt(cursor.getColumnIndex("width"));
			
			height = cursor.getInt(cursor.getColumnIndex("height"));
			System.out.println("--------------------------");
			System.out.println("path = " + path);
			System.out.println("display = " + display);
			System.out.println("date = " + new Date(date));
			System.out.println("size = " + size);
			System.out.println("width = " + width);
			System.out.println("height = " + height);
		}
    }
}

 显示媒体库中的图片
              在显示媒体库中的图片时，容易因为图片大小不一致而引发一下OOM的错误


            OOM解决方案
   在一次性加载（无视是在主线程或子线程）大量数据时容易导致OOM（Out if Memory Error）;
            在加载图片时出现OOM，可以试着使用以下的解决方法：
            在使用BitmapFactory类decode图片时，设置Options参数，将图片缩小显示；
    使用Thumbnails生成缩略图的Bitmap对象在显示；
核心代码： 

Image：

	      public class Image {
	private String path;
	private String display;
	private long date;
	private int size;
	private int width;
	private int height;
	private long id;
	
	public long getId() {
		return id;
	}
	public void setId(long id) {
		this.id = id;
	}
	public String getPath() {
		return path;
	}
	public void setPath(String path) {
		this.path = path;
	}
	public String getDisplay() {
		return display;
	}
	public void setDisplay(String display) {
		this.display = display;
	}
	public long getDate() {
		return date;
	}
	public void setDate(long date) {
		this.date = date;
	}
	public int getSize() {
		return size;
	}
	public void setSize(int size) {
		this.size = size;
	}
	public int getWidth() {
		return width;
	}
	public void setWidth(int width) {
		this.width = width;
	}
	public int getHeight() {
		return height;
	}
	public void setHeight(int height) {
		this.height = height;
	}
	
}

        ImageAdapter：

         public class ImageAdapter extends BaseAdapter {
	private List<Image> images;

	public ImageAdapter(List<Image> images) {
		setImages(images);
	}

	private void setImages(List<Image> images) {
		if (images == null) {
			images = new ArrayList<Image>();
		}
		this.images = images;
	}

	@Override
	public int getCount() {
		// TODO Auto-generated method stub
		return images.size();
	}

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {

       ViewHolder holder;
       if(convertView == null){
    	   holder = new ViewHolder();
    	   convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.lv_item, null);
    	   holder.image = (ImageView)convertView.findViewById(R.id.iv_image);
    	   holder.path = (TextView)convertView.findViewById(R.id.tv_item_path);
    	   holder.display = (TextView)convertView.findViewById(R.id.tv_item_name);
    	   holder.px = (TextView)convertView.findViewById(R.id.tv_item_px);
    	   holder.size = (TextView)convertView.findViewById(R.id.tv_item_size);
    	   
    	   convertView.setTag(holder);
       }else{
    	   holder = (ViewHolder) convertView.getTag();
       }
       Image img = images.get(position);
       //容易导致OOM问题，Bitmap对象太大
       //Bitmap bm = BitmapFactory.decodeFile(img.getPath());
       Bitmap bm;
//       方法一：自定义方法获取Bitmap
//       bm = decodeFile(img);
//       方法二：使用Thumbnails
       bm = Thumbnails.getThumbnail(parent.getContext().getContentResolver(), img.getId(), Thumbnails.MICRO_KIND, null);
       holder.display.setText(img.getDisplay());
       holder.size.setText(img.getSize() / 1024+ "KB");
       holder.path.setText(img.getPath());
       holder.px.setText(img.getWidth() + " x " + img.getHeight() + "px");
		holder.image.setImageBitmap(bm);
       return convertView;
	}

	static final int MAX_WIDTH = 80;
	static final int MAX_HEIGHT = 80;
	private Bitmap decodeFile(Image img){
		
		Bitmap bm = null;
		Options opts = new Options();
		int rate;
//		未知图片的宽与高时的做法：
		opts.inJustDecodeBounds = true;
		bm = BitmapFactory.decodeFile(img.getPath(),opts);
		int width = opts.outWidth;
		int height = opts.outHeight;
		if(width >height){
			rate = height / MAX_HEIGHT - 1;
		}else{
			rate = width / MAX_WIDTH - 1;
		}
		opts.inJustDecodeBounds = false;
//		当已知图片的宽与高时，可以使用以下的方法
//		if(img.getWidth() > img.getHeight()){
//			rate = img.getWidth() / MAX_WIDTH - 1;
//		}else{
//			rate = img.getHeight() / MAX_HEIGHT - 1;
//		}
		opts.inSampleSize = rate;
		bm = BitmapFactory.decodeFile(img.getPath(),opts);
		return bm;
	}
	private class ViewHolder {
		ImageView image;
		TextView path, display, px, size;
	}

	@Override
	public Object getItem(int position) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public long getItemId(int position) {
		// TODO Auto-generated method stub
		return 0;
	}

}

MainActivity：

   public class MainActivity extends Activity {
	
	private List<Image> images = new ArrayList<Image>();
	private ListView listView;
	private ImageAdapter adapter;
    @Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		loadImages();
		
		listView = (ListView) findViewById(R.id.lv_images);
		adapter = new ImageAdapter(images);
		listView.setAdapter(adapter);
    }
    private void loadImages(){
    	ContentResolver cr = getContentResolver();
		Uri uri = Media.EXTERNAL_CONTENT_URI;
		Cursor cursor  = cr.query(uri, null, null, null, null);
//		Image image = new Image();
		for(cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()){
			Image image = new Image();
			image.setId(cursor.getLong(cursor.getColumnIndex(Media._ID)));
			image.setPath(cursor.getString(cursor.getColumnIndex(Media.DATA)));
			image.setDisplay(cursor.getString(cursor.getColumnIndex(Media.DISPLAY_NAME)));
			image.setDate(cursor.getLong(cursor.getColumnIndex(Media.DATE_TAKEN)));
			image.setSize(cursor.getInt(cursor.getColumnIndex(Media.SIZE)));
			image.setWidth(cursor.getInt(cursor.getColumnIndex("width")));
			image.setHeight(cursor.getInt(cursor.getColumnIndex("height")));
			images.add(image);
		}
		cursor.close();
    }
}

布局：
      activity_main:

         <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <ListView 
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/lv_images"></ListView>
</LinearLayout>

item布局：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
    <ImageView 
        android:id="@+id/iv_image"
        android:layout_width="60dp"
        android:layout_height="60dp"
        android:src="@drawable/ic_launcher"/>
    
    <RelativeLayout 
        android:id="@+id/rl_item"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:layout_marginLeft="10dp"
        android:layout_toRightOf="@+id/iv_image">
        <TextView
            android:id="@+id/tv_item_name"
            android:layout_width="match_parent"
            android:layout_height="20dp"
            android:textSize="16sp"
            android:gravity="left|center"
            android:textStyle="bold"
             android:singleLine="true"
            android:text="im01.jpg"/>
        <TextView
            android:id="@+id/tv_item_px"
            android:textSize="12sp"
            android:textColor="#666666"
            android:gravity="left|center"
            android:layout_width="wrap_content"
            android:layout_height="20dp"
            android:text="1200 X 345px    "
             android:singleLine="true"
            android:layout_below="@+id/tv_item_name"
            
            />
        <TextView
            android:id="@+id/tv_item_size"
            android:layout_width="match_parent"
            android:layout_height="20dp"
            android:textSize="12sp"
            android:gravity="left|center"
            android:textColor="#666666"
            android:text="234kb"
             android:singleLine="true"
            android:layout_toRightOf="@+id/tv_item_px"
            android:layout_alignTop="@+id/tv_item_px"/>
        <TextView
            android:id="@+id/tv_item_path"
            android:layout_width="match_parent"
            android:layout_height="20dp"
            android:textSize="12sp"
            android:textColor="#666666"
            android:gravity="left|center"
            android:singleLine="true"
            android:layout_below="@+id/tv_item_px"
            android:text="D:world/nicai/nicaii/zaicai.png"/>
            
        
    </RelativeLayout>

</RelativeLayout>

访问媒体库中的音频  代码：

package com.example.lianxi;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import android.app.Activity;
import android.content.ContentResolver;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore.Audio.Media;
import android.widget.ListView;

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		// 媒体库中的音频所具有的部分字段：
		// _id _data titile_size duration album_artist album album_key
		// ContentResolver Uri
		ContentResolver cr = getContentResolver();
		Uri uri = Media.EXTERNAL_CONTENT_URI;
		Cursor cursor = cr.query(uri, null, null, null, null);
		List<Music> musics = new ArrayList<Music>();
		Music music;
		for (cursor.moveToFirst(); cursor.isAfterLast(); cursor.moveToNext()) {
			music = new Music();
			music.setId(cursor.getLong(cursor.getColumnIndex(Media._ID)));
			music.setData(cursor.getString(cursor.getColumnIndex(Media.DATA)));
			music.setTitle(cursor.getString(cursor.getColumnIndex(Media.TITLE)));
			music.setArtist(cursor.getString(cursor
					.getColumnIndex(Media.ARTIST)));
			music.setAlbum(cursor.getString(cursor.getColumnIndex(Media.ALBUM)));
			music.setAlbumkey(cursor.getString(cursor
					.getColumnIndex(Media.ALBUM_KEY)));
			music.setSize(cursor.getInt(cursor.getColumnIndex(Media.SIZE)));
			music.setDuration(cursor.getInt(cursor
					.getColumnIndex(Media.DURATION)));
			musics.add(music);
			System.out.println(music.toString());

		}
		cursor.close();
	}
}

测试结果：

 01-01 13:41:27.514: I/System.out(11445): Music [id=15, data=/storage/emulated/0/Music/Groove Coverage - She.mp3, title=Groove Coverage - She, size=3664535, duration=229033, artist=<unknown>, album=Music]
01-01 13:41:27.518: I/System.out(11445): Music [id=16, data=/storage/emulated/0/Music/number2.mp3, title=number2, size=3664535, duration=229033, artist=<unknown>, album=Music]
01-01 13:41:27.530: I/System.out(11445): Music [id=17, data=/storage/emulated/0/Music/number3.mp3, title=Can't Get You Out Of My Head, size=3681031, duration=230016, artist=Kylie Minogue, album=Can't Get You Out of My Head [UK CD]]
01-01 13:41:27.530: I/System.out(11445): Music [id=18, data=/storage/emulated/0/Music/number1.mp3, title=number1, size=4727537, duration=295471, artist=<unknown>, album=Music]

使用媒体库做出的获取音乐信息

与获取图片类似

MusicAdapter：

public class MusicAdapter extends BaseAdapter{

	private List<Music> musics;
	public MusicAdapter(List<Music> musics){
		setMusics(musics);
	}
	public void setMusics(List<Music> musics){
		if(musics == null){
			musics = new ArrayList<Music>();
		}
		this.musics = musics;
	}
	@Override
	public int getCount() {
		// TODO Auto-generated method stub
		return musics.size();
	}

	private class ViewHolder{
		ImageView image;
		TextView title,duration,artist,album;
	}
	@Override
	public Object getItem(int position) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public long getItemId(int position) {
		// TODO Auto-generated method stub
		return 0;
	}

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		// TODO Auto-generated method stub
		ViewHolder holder;
		if(convertView == null){
			convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.lv_item, null);
			holder = new ViewHolder();
			holder.image = (ImageView) convertView.findViewById(R.id.iv_image);
			holder.title = (TextView) convertView.findViewById(R.id.tv_item_title);
			holder.duration = (TextView) convertView.findViewById(R.id.tv_item_time);
			holder.artist = (TextView) convertView.findViewById(R.id.tv_item_artist);
			holder.album = (TextView) convertView.findViewById(R.id.tv_item_name);
		    convertView.setTag(holder);
		}else{
			holder = (ViewHolder) convertView.getTag();
		}
		Music music = musics.get(position);
		
		holder.title.setText(music.getTitle());
		holder.duration.setText(formatDuration(music.getDuration()));
		holder.artist.setText(music.getArtist());
		holder.album.setText(music.getAlbum());
		
		if(music.getImagePath() == null){
			
		}else{
			holder.image.setImageBitmap(BitmapFactory.decodeFile(music.getImagePath()));
		}
		
		return convertView;
	}
	private String formatDuration(int duration){
		return new SimpleDateFormat("mm:ss",Locale.CHINA).format(new Date(duration));
	}

}

Music：

public class Music {
      private long id;
      private String data;
      private String title;
      private int size;
      private int duration;
      private String artist;
      private String album;
      private String albumkey;
      private String imagePath;
      
	public String getImagePath() {
		return imagePath;
	}
	public void setImagePath(String imagePath) {
		this.imagePath = imagePath;
	}
	public String getArtist() {
		return artist;
	}
	public void setArtist(String artist) {
		this.artist = artist;
	}
	public long getId() {
		return id;
	}
	public void setId(long id) {
		this.id = id;
	}
	public String getData() {
		return data;
	}
	public void setData(String data) {
		this.data = data;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public int getSize() {
		return size;
	}
	public void setSize(int size) {
		this.size = size;
	}
	public int getDuration() {
		return duration;
	}
	public void setDuration(int duration) {
		this.duration = duration;
	}
	public String getAlbum() {
		return album;
	}
	public void setAlbum(String album) {
		this.album = album;
	}
	public String getAlbumkey() {
		return albumkey;
	}
	public void setAlbumkey(String albumkey) {
		this.albumkey = albumkey;
	}
	@Override
	public String toString() {
		return "Music [id=" + id + ", data=" + data + ", title=" + title
				+ ", size=" + size + ", duration=" + duration + ", artist="
				+ artist + ", album=" + album + "]";
	}
	
      
}

MainActivity：

public class MainActivity extends Activity {
	
	private List<Music> musics;
	private ListView listView;
	private MusicAdapter adapter;
	private Uri uri;
	private Cursor cursor;
	private ContentResolver cr;
    @Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		loadMusic();
		listView = (ListView) findViewById(R.id.lv_images);
		adapter = new MusicAdapter(musics);
		listView.setAdapter(adapter);
	
    }
    private void loadMusic(){
    	cr = getContentResolver();
		uri = Media.EXTERNAL_CONTENT_URI;
		cursor = cr.query(uri, null, null, null, null);
       musics = new ArrayList<Music>();
       for(cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()){
    	   Music music = new Music();
    	   music.setId(cursor.getLong(cursor.getColumnIndex(Media._ID)));
    	   music.setData(cursor.getString(cursor.getColumnIndex(Media.DATA)));
    	   music.setTitle(cursor.getString(cursor.getColumnIndex(Media.TITLE)));
    	   music.setArtist(cursor.getString(cursor.getColumnIndex(Media.ARTIST)));
    	   music.setAlbum(cursor.getString(cursor.getColumnIndex(Media.ALBUM)));
    	   music.setAlbumkey(cursor.getString(cursor.getColumnIndex(Media.ALBUM_KEY)));
    	   music.setSize(cursor.getInt(cursor.getColumnIndex(Media.SIZE)));
    	   music.setDuration(cursor.getInt(cursor.getColumnIndex(Media.DURATION)));
    	   System.out.println(music.toString());
    	   Uri imageUri = Albums.EXTERNAL_CONTENT_URI;
    	   String[] projection = new String[] {Albums.ALBUM_ART};
		String selection = Albums.ALBUM_KEY + "=?";
		String[] selectionArgs = new String[] {music.getAlbumkey()};
		Cursor imageCursor = cr.query(imageUri, projection, selection, selectionArgs, null);
    	if(imageCursor.moveToFirst()){
    		music.setImagePath(imageCursor.getString(0));
    	}
		musics.add(music);  
    	   
       }
       cursor.close();
    }
}

布局与获取照片信息布局类似，这里不再贴出代码