DownloadManager是Android為開發(fā)者提供的一個后臺應用組件，它通過Http層進行文件的下載任務.
    1：使用
         首先要在AndroidManifest.xml中申請訪問DownloadManager的權(quán)限
          <permission android:name="android.permission.ACCESS_DOWNLOAD_MANAGER"/>
         添加一個下載任務：
         ContentValues values = new ContentValues();
         values.put(Downloads.URI, url);//指定下載地址
        values.put(Downloads.COOKIE_DATA, cookie);//如果下載Server需要cookie,設(shè)置cookie
        values.put(Downloads.VISIBILITY,Downloads.VISIBILITY_HIDDEN);//設(shè)置下載提示是否在屏幕頂部顯示
        values.put(Downloads.NOTIFICATION_PACKAGE, getPackageName());//設(shè)置下載完成之后回調(diào)的包名
        values.put(Downloads.NOTIFICATION_CLASS, DownloadCompleteReceiver.class.getName());//設(shè)置下載完成之后負責接收的Receiver，這個類要繼承 BroadcastReceiver     
        values.put(Downloads.DESTINATION,save_path);//設(shè)置下載到的路徑，這個需要在Receiver里自行處理
        values.put(Downloads.TITLE,title);//設(shè)置下載任務的名稱
        this.getContentResolver().insert(Downloads.CONTENT_URI, values);//將其插入到DownloadManager的數(shù)據(jù)庫中，數(shù)據(jù)庫會觸發(fā)修改事件，啟動下載任務


   2：如何為DownloadManager設(shè)置代理，比如Wap
             values.put(Downloads.PROXY_HOST,"10.0.0.172");
            values.put(Downloads.PROXY_PORT,"80");


  3:如何在下載過程中監(jiān)聽下載任務
     可以通過監(jiān)聽數(shù)據(jù)庫來實現(xiàn)
    DownloadsChangeObserver mDownloadObserver=new DownloadsChangeObserver(Downloads.CONTENT_URI);
    private class DownloadsChangeObserver extends ContentObserver {
        public DownloadsChangeObserver(Uri uri) {
            super(new Handler());
        }
        @Override
        public void onChange(boolean selfChange) {
            //查詢需要監(jiān)聽的字段
           //比如要監(jiān)聽實時下載進度，查看當前下載狀態(tài)：是否已經(jīng)斷開，或者下載失敗等等
           StringBuilder wherequery = new StringBuilder(Downloads.TITLE);
            wherequery.append("=");
            wherequery.append("'");
            wherequery.append(mTitle);
            wherequery.append("'");

           mDownloadCursor =mContext.getContentResolver().query(Downloads.CONTENT_URI, new String[] {Downloads.TITLE, Downloads.STATUS, Downloads.CURRENT_BYTES，}, wherequery.toString(), null,orderBy)；        
            int mSizeColunmId=mDownloadCursor.getColumnIndexOrThrow(Downloads.CURRENT_BYTES);   
           mDownloadCursor.moveToFirst();    
            int size=mDownloadCursor.getInt(mSizeColunmId);
       ｝
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  4：如何刪除下載記錄
    private void deleteHistory(String title)//刪除掉指定名稱的下載記錄
    { 
        StringBuilder whereDelete = new StringBuilder(Downloads.TITLE);
        whereDelete.append("=");
        whereDelete.append("'");
        whereDelete.append(str);
        whereDelete.append("'");
        this.getContentResolver().delete(Downloads.CONTENT_URI,whereDelete.toString(), null);
    }   

https://github.com/commonsguy/cw-android/tree/master/Internet/Download
http://hi-android.info/src/com/android/providers/downloads/DownloadProvider.java.html