Downloadmanager使用

DownloadManager是android提供的一个下载管理器

缺点：不支持断点续传

使用方法:

1. 创建实例:

   DownloadManager manager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);

2. 创建下载任务:

   DownloadManager.Request request = new DownloadManager.Request(Uri.parse(URL));
   //指定保存地址
   request.setDestinationInExternalPublicDir("chuyi", "meizhi.apk");
   //设置允许下载的网络状况
   request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);
   //设置通知栏的行为
   request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
   //通过id唯一标识此下载任务
   long id = manager.enqueue(request);

3. 删除下载任务:

   manager.remove(id);

4. 查询下载任务:

   DownloadManager.Query query = new DownloadManager.Query();
   query.setFilterById(id);
   Cursor cursor = manager.query(query);
   
   if(cursor.moveToFirst()){
       String filename = cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME));
       String fileUri = cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));
       Toast.makeText(context,"下载完成...name:"+filename+",uri:"+fileUri,Toast.LENGTH_SHORT).show();
   }else {
     //TODO
   }
   cursor.close();

5. 查询下载进度:

   DownloadManager.Query query = new DownloadManager.Query().setFilterById(downloadId);
   Cursor c = null;
   try {
       c = downloadManager.query(query);
       if (c != null && c.moveToFirst()) {
           int downloadedBytes = c.getInt(c.getColumnIndexOrThrow(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR));
           int totalBytes = c.getInt(c.getColumnIndexOrThrow(DownloadManager.COLUMN_TOTAL_SIZE_BYTES));
           int state = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
       }
   } finally {
       if (c != null) {
           c.close();
       }
   }
   

6. 监听下载结束通知:

   可以通过接收DownloadManager.ACTION_DOWNLOAD_COMPLETE广播来监听下载结束的通知

   IntentFilter filter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);
       mReceiver = new BroadcastReceiver(){
         public void onReceive(Context c,Intent i){
             long downId = i.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID,-1);
         }
       }
       context.registerReceiver(mReceiver,filter);

7. 监听下载进度:

   主要有三种方案：1.FileReceiver 2.ContentObserver 3.定时任务

   class DownloadChangeObserver extends ContentObserver {
   
   public DownloadChangeObserver(){
       super(handler);
   }
   
   @Override
   public void onChange(boolean selfChange) {
       //查询进度
   }
   
   }
   //in activity
   private DownloadChangeObserver downloadObserver;
   
   @Override
   protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.download_manager_demo);
   ……
   downloadObserver = new DownloadChangeObserver();
   }
   
   @Override
   protected void onResume() {
       super.onResume();
       /** observer download change **/
       getContentResolver().registerContentObserver(DownloadManagerPro.CONTENT_URI, true,
                                                    downloadObserver);
   }
   
   @Override
   protected void onPause() {
       super.onPause();
       getContentResolver().unregisterContentObserver(downloadObserver);
   }

   上面这种做法可能对性能有些损耗，因为会不断触发onChange

   推荐使用ScheduledExecutorService

   public static ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3);
   Runnable command = new Runnable() {
   
       @Override
       public void run() {
           updateView();
       }
   };
   scheduledExecutorService.scheduleAtFixedRate(command, 0, 3, TimeUnit.SECONDS);

   参考资料：

   1. http://www.trinea.cn/android/android-downloadmanager/
   2. http://www.trinea.cn/android/android-downloadmanager/
   3. https://github.com/Trinea/android-common/blob/master/src/cn/trinea/android/common/util/DownloadManagerPro.java