安卓系統媒體庫

安卓系統媒體庫
Android系統的媒體檔案管理方式：
掃描存放裝置上的公有媒體檔案，並使用SQLite資料庫記錄下相關的資訊：
一般情況下，系統開機時會發出媒體掃描的廣播，通知掃描程式進行掃描；
開發人員開發的應用程式也可以調用掃描器即時掃描；
掃描到的媒體除了會在資料庫中記錄媒體檔案的路徑意外，還會記錄下其他的相關資訊，例如入庫的時間、修改時間、圖片詳情、歌曲時間長度等；
Android系統使用的ContentProvider以使得裝置上的其他應用程式可以隨時訪問這些媒體資料。
訪問媒體庫：系統中包名為com.android.providers.media的應用程式提供了媒體庫的ContentProvider；
如何訪問媒體庫中的圖片資訊

方法：

 

public class MainActivity extends Activity {    @Overrideprotected 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);}    }}

顯示媒體庫中的圖片
在顯示媒體庫中的圖片時，容易因為圖片大小不一致而引發一下OOM的錯誤


OOM解決方案
在一次性載入（無視是在主線程或子線程）大量資料時容易導致OOM（Out if Memory Error）;
在載入圖片時出現OOM，可以試著使用以下的解決方案：
在使用BitmapFactory類decode圖片時，設定Options參數，將圖片縮小顯示；
使用Thumbnails產生縮圖的Bitmap對象在顯示；
核心代碼：

 

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

images; public ImageAdapter(List images) { setImages(images); } private void setImages(List images) { if (images == null) { images = new ArrayList(); } 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); //容易導致OOM問題，Bitmap對象太大 //Bitmap bm = BitmapFactory.decodeFile(img.getPath()); Bitmap bm; // 方法一：自訂方法擷取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; // 未知圖片的寬與高時的做法： 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; // 當已知圖片的寬與高時，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

images = new ArrayList(); 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:

 

 

item布局：

 

 

訪問媒體庫中的音頻 代碼：

 

 

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 {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);// 媒體庫中的音頻所具有的部分欄位：// _id _data titile_size duration album_artist album album_key// ContentResolver UriContentResolver cr = getContentResolver();Uri uri = Media.EXTERNAL_CONTENT_URI;Cursor cursor = cr.query(uri, null, null, null, null);List musics = new ArrayList();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();}}

測試結果：

 

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=, 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=, 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=, album=Music]

使用媒體庫做出的擷取音樂資訊

與擷取圖片類似

MusicAdapter：

 

public class MusicAdapter extends BaseAdapter{private List musics;public MusicAdapter(List musics){setMusics(musics);}public void setMusics(List musics){if(musics == null){musics = new ArrayList();}this.musics = musics;}@Overridepublic int getCount() {// TODO Auto-generated method stubreturn musics.size();}private class ViewHolder{ImageView image;TextView title,duration,artist,album;}@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn null;}@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// TODO Auto-generated method stubViewHolder 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;}@Overridepublic 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 musics;private ListView listView;private MusicAdapter adapter;private Uri uri;private Cursor cursor;private ContentResolver cr;    @Overrideprotected 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();       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();    }}

布局與擷取照片資訊布局類似，這裡不再貼出代碼