private void broadcast(final long Id) {
 
		// 注册广播监听系统的下载完成事件。
		IntentFilter intentFilter = new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE);
		broadcastReceiver = new BroadcastReceiver() {
			@Override
			public void onReceive(Context context, Intent intent) {
				long ID = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, -1);
				if (ID == Id) {
					Toast.makeText(getApplicationContext(), "任务:" + Id + " 下载完成!", Toast.LENGTH_LONG).show();
				}
			}
		};
 
		registerReceiver(broadcastReceiver, intentFilter);
	}