查看你是否设置Type类型。
req.setMimeType("application/vnd.android.package-archive");
这句话的意思是，在DownloadManager添加之初就指定该下载文件为APK文件。
具体添加位置：
public long startDownload(String uri, String title, String description) {
DownloadManager.Request req = new DownloadManager.Request(Uri.parse(uri));
req.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI);
req.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
req.setMimeType("application/vnd.android.package-archive");
req.setTitle(title);
req.setDescription(description);
return dm.enqueue(req);
//long downloadId = dm.enqueue(req);
//Log.d("DownloadManager", downloadId + "");
//dm.openDownloadedFile()
}
