无法在android中获取下载管理器的状态

Question

我正在使用android.I我正在尝试使用下载管理器获取下载状态。但它不起作用。我使用了以下代码

    DownloadManager.Query query = null;
    Log.i("service1", "blah");
    Cursor c = null;
    DownloadManager downloadManager = null;
    downloadManager = (DownloadManager)getSystemService(Context.DOWNLOAD_SERVICE);
    Log.i("service2", "blah");
    query = new DownloadManager.Query();
     if(query!=null) {
         Log.i("service3", "blah");
                query.setFilterByStatus(DownloadManager.STATUS_FAILED|DownloadManager.STATUS_PAUSED|DownloadManager.STATUS_SUCCESSFUL|
                        DownloadManager.STATUS_RUNNING|DownloadManager.STATUS_PENDING);
            } else {
                Log.i("service4", "blah");
                return;
            }
    c = downloadManager.query(query);
    if(c.moveToFirst()) { 
        Log.i("service5", "blah");
    int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS)); 
    Log.i("service6", "blah");
    switch(status) { 
    case DownloadManager.STATUS_PAUSED: 
    break; 
    case DownloadManager.STATUS_PENDING: 
    break; 
    case DownloadManager.STATUS_RUNNING: 
        Toast.makeText(this, "Download started", Toast.LENGTH_SHORT).show();
    break; 
    case DownloadManager.STATUS_SUCCESSFUL: 
        Toast.makeText(this, "Download completed", Toast.LENGTH_SHORT).show();
    break; 
    case DownloadManager.STATUS_FAILED: 
    break; 
    }
   }

它不会进入if（c.moveToFirst（））。或者在Android中获取下载状态的任何其他方式？