android - DownloadManager 没有开始下载文件

Question

假设我要下载这个文件(随机文件): http://www.analysis.im/uploads/seminar/pdf-sample.pdf

这是我的代码:

DownloadManager.Request req = new DownloadManager.Request(Uri.parse("http://www.analysis.im/uploads/seminar/pdf-sample.pdf"));

req.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI | DownloadManager.Request.NETWORK_MOBILE)
   .setAllowedOverRoaming(false)
   .setTitle("Random title")
   .setDescription("Random description")
   .setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "pdf-sample.pdf");

在 Debug模式下，我可以看到所有参数都是正确的，为什么下载没有开始？

编辑

我当前的权限:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.INTERNET"/>

Answer 1

你允许在DownloadManager.Request.NETWORK_MOBILE的网络类型下下载，但为什么要设置setAllowedOverRoaming(false)？

我尝试使用 Downloadmanager 下载文件，这是我的代码:

String url = "http://example.com/large.zip";
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));

// only download via WIFI
request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);
request.setTitle("Example");
request.setDescription("Downloading a very large zip");

// we just want to download silently
request.setVisibleInDownloadsUi(false);
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_HIDDEN);
request.setDestinationInExternalFilesDir(context, null, "large.zip");

// enqueue this request
DownloadManager downloadManager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
downloadID = downloadManager.enqueue(request);

希望您有所启发。