我可以下载一个文件并保存在下载文件夹中：

DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
    request.setDescription(descricao);
    request.setTitle(titulo);

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        request.allowScanningByMediaScanner();
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
    }
    request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS,nome);

    enq = downloadManager.enqueue(request);

在此之后,我的文件在目录文件夹中保存正确：Android>>内部共享存储>>下载.
***我看到这条路径在ubuntu中手动打开设备的高清.由于图像显示路径.
Android HD by ubuntu folder – see the path

我尝试用这个打开这个文件：

downloadManager = (DownloadManager)getContext().getSystemService(DOWNLOAD_SERVICE);
        BroadcastReceiver receiver = new 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.Query query = new DownloadManager.Query();
                    query.setFilterById(enq);
                    Cursor c = downloadManager.query(query);
                    if(c.moveToFirst()) {
                        int columnIndex = c.getColumnIndex(DownloadManager.COLUMN_STATUS);
                        if(DownloadManager.STATUS_SUCCESSFUL == c.getInt(columnIndex)) {
                            String uriString = c.getString(c.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI));

                            if (uriString.substring(0,7).matches("file://")) {
                                uriString =  uriString.substring(7);
                            }

                            File file = new File(uriString);

                            Uri uriFile = FileProvider.getUriForFile(getContext(),BuildConfig.APPLICATION_ID + ".fileprovider",file);
                            String mimetype = "application/pdf";
                            Intent myIntent = new Intent(Intent.ACTION_VIEW);
                            myIntent.setDataAndType(uriFile,mimetype);

                            Intent intentChooser = Intent.createChooser(myIntent,"Choose Pdf Application");
                            startActivity(intentChooser);
                        }
                    }
                }
            }
        };

        getContext().registerReceiver(receiver,new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));

我在清单中声明我的文件提供程序：

<provider
        android:name="android.support.v4.content.FileProvider"
        android:authorities="${applicationId}.fileprovider"
        android:exported="false"
        android:grantUriPermissions="true">
        <Meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/provider_paths"/>
    </provider>

并与此：

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="Download" path="Download/"/>
</paths>

但是,当我单击按钮下载时,我收到此消息：“此文件无法访问.请检查位置或网络,然后重试.”

恢复：

1 – 文件已下载并保存在目录文件夹中.

2 – 意图已启动,但文件未打开.

3 – 调试模式在“new File(urlString)”中给出了这个：“urlString = / storage / emulated / 0 / Download / name.pdf”

4 – 在“FileProvider.getUriFromFile …”调试模式具有：

“uriFile = content：//com.example.android.parlamentaresapp.fileprovider/Download/name.pdf”

谢谢.