Android DownloadManager下载文件时，会先下载一个临时文件，然后在下载完成时将其重命名为实际文件。但是，如果您使用默认的下载完成通知打开文件，它将打开这个临时文件，而不是实际文件。

以下是解决此问题的代码示例：

1.创建一个BroadcastReceiver处理DOWNLOAD_COMPLETE action：

public class DownloadReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (DownloadManager.ACTION_DOWNLOAD_COMPLETE.equals(action)) {
            long downloadId = intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, 0);
            DownloadManager downloadManager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
            DownloadManager.Query query = new DownloadManager.Query();
            query.setFilterById(downloadId);
            Cursor cursor = downloadManager.query(query);
            if (cursor.moveToFirst()) {
                int status = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS));
                if (status == DownloadManager.STATUS_SUCCESSFUL) {
                    String uriString = cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));
                    Uri uri = null;
                    if (uriString != null) {
                        uri = Uri.parse(uriString);
                        if (uri != null) {
                            String mime = downloadManager.getMimeTypeForDownloadedFile(downloadId);
                            Intent viewIntent = new Intent(Intent.ACTION_VIEW);
                            viewIntent.setDataAndType(uri, mime);
                            viewIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                            context.startActivity(viewIntent);
                        }
                    }
                }
            }
            cursor.close();
        }
    }
}

2.在AndroidManifest.xml中注册BroadcastReceiver：

使用此方法，当下载完成时，我们可以获取实际文件的URI并使用适当的Intent打开它。