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C# UWP using System.IO.Directory return empty array?

i am trying to return all the files contain in a folder in UWP application for Windows 10, the code is shown below:
var path = #"C:\Users\Desktop";
var files = System.IO.Directory.GetFiles(path); //get empty arrays
But, i get empty string arrays, may I know what causes this problem?

You can't. For uwp and store apps, only the app installation and app temp folders are granted for direct access. 'Direct' means ... accesses without Windows.Storge broker process. (System.IO is 'direct'.)
If you want to access the 'outside' of your app - like as desktop, you need to ask user to pick the location by File/FolderPicker. Without the user interaction, you can't access.
However, Windows.Storage broker service provide the rich methods for file operation, and additional functions like as CommnonQuery features.
There are some exception for pictures, video folders, but the basic concept is same.
Following link may helps you. :)
File access permissions

Probably because C:\Users\Desktop doesn't exist on the system - it would be under C:\Users\YOUR_USERNAME\Desktop.
Additionally, your application might be operating in a sandbox, so all filesystem access will be virtualized to a private silo elsewhere - Windows would pretend that the directory you specified exists but says it's empty, because it doesn't want you accessing the user's files without prior permission.

Windows 10 Universal App File/Directory Access

I´m developing an app that is reading jpeg and pdf files from a configurable location on the filesystem.
Currently there is a running version implemented in WPF and now I´m trying to move to the new Windows Universal apps.
The following code works fine with WPF:
public IList<string> GetFilesByNumber(string path, string number)
{
if (string.IsNullOrWhiteSpace(path))
throw new ArgumentNullException(nameof(path));
if (string.IsNullOrWhiteSpace(number))
throw new ArgumentNullException(nameof(number));
if (!Directory.Exists(path))
throw new DirectoryNotFoundException(path);
var files = Directory.GetFiles(path, "*" + number + "*",
SearchOption.AllDirectories);
if (files == null || files.Length == 0)
return null;
return files;
}
With using Universal Apps I ran into some problems:
Directory.Exists is not available
How can I read from directories outside of my app storage?
To read from an other directory outside the app storage I tried the following:
StorageFolder folder = StorageFolder.GetFolderFromPathAsync("D:\\texts\\");
var fileTypeFilter = new string[] { ".pdf", ".jpg" };
QueryOptions queryOptions = new QueryOptions(CommonFileQuery.OrderBySearchRank, fileTypeFilter);
queryOptions.UserSearchFilter = "142";
StorageFileQueryResult queryResult = folder.CreateFileQueryWithOptions(queryOptions);
IReadOnlyList<StorageFile> files = queryResult.GetFilesAsync().GetResults();
The thing is: It isn´t working, but I get an exception:
An exception of type 'System.UnauthorizedAccessException' occurred in TextManager.Universal.DataAccess.dll but was not handled in user code
Additional information: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
I know that you have to configure some permissions in the manifest, but I can´t find one suitable for filesystem IO operations...
Did someone also have such problems/a possible solution?
Solution:
From the solutions that #Rico Suter gave me, I chosed the FutureAccessList in combination with the FolderPicker. It is also possible to access the entry with the Token after the program was restarted.
I can also recommend you the UX Guidlines and this Github sample.
Thank you very much!

In UWP apps, you can only access the following files and folders:
Directories which are declared in the manifest file (e.g. Documents, Pictures, Videos folder)
Directories and files which the user manually selected with the FileOpenPicker or FolderPicker
Files from the FutureAccessList or MostRecentlyUsedList
Files which are opened with a file extension association or via sharing
If you need access to all files in D:\, the user must manually pick the D:\ drive using the FolderPicker, then you have access to everything in this drive...
UPDATE:
Windows 10 build 17134 (2018 April Update, version 1803) added additional file system access capabilities for UWP apps:
Any UWP app (either a regular windowed app or a console app) that declares an AppExecutionAlias is now granted implicit access to the files and folders in the current working directory and downward, when it’s activated from a command line. The current working directory is from whatever file-system location the user chooses to execute your AppExecutionAlias.
The new broadFileSystemAccess capability grants apps the same access to the file system as the user who is currently running the app without file-picker style prompts. This access can be set in the manifest in the following manner:
xmlns:rescap="http://schemas.microsoft.com/appx/manifest/foundation/windows10/restrictedcapabilities"
...
IgnorableNamespaces="uap mp uap5 rescap">
...
<Capabilities>
<rescap:Capability Name="broadFileSystemAccess" />
</Capabilities>
These changes and their intention are discussed at length in the MSDN Magazine article titled Universal Windows Platform - Closing UWP-Win32 Gaps. The articles notes the following:
If you declare any restricted capability, this triggers additional
scrutiny at the time you submit your package to the Store for
publication. ... You don’t need an AppExecutionAlias if you have this
capability. Because this is such a powerful feature, Microsoft will
grant the capability only if the app developer provides compelling
reasons for the request, a description of how this will be used, and
an explanation of how this benefits the user.
further:
If you declare the broadFileSystemAccess capability, you don’t need to
declare any of the more narrowly scoped file-system capabilities
(Documents, Pictures or Videos); indeed, an app must not declare both
broadFileSystemAccess and any of the other three file-system
capabilities.
finally:
Even after the app has been granted the capability, there’s also a
runtime check, because this constitutes a privacy concern for the
user. Just like other privacy issues, the app will trigger a
user-consent prompt on first use. If the user chooses to deny
permission, the app must be resilient to this.

The accepted answer is no longer complete. It is now possible to declare broadFileSystemAccess in the app manifest to arbitrarily read the file system.
The File Access Permissions page has details.
Note that the user can still revoke this permission via the settings app.

You can do it from UI in VS 2017.
Click on manifest file -> Capabilities -> Check photo library or whatever stuff you want.

According to MSDN doc : "The file picker allows an app to access files and folders, to attach files and folders, to open a file, and to save a file."
https://msdn.microsoft.com/en-us/library/windows/apps/hh465182.aspx
You can read a file using the filepicker through a standard user interface.
Regards

this is not true:
Files which are opened with a file extension association or via sharing
try it, by opening files from mail (outlook) or from the desktop...
it simply does not work
you first have to grant the rights by the file picker.
so this ist sh...

This is a restricted capability. Access is configurable in Settings > Privacy > File system. and enable acces for your app. Because users can grant or deny the permission any time in Settings, you should ensure that your app is resilient to those changes. If you find that your app does not have access, you may choose to prompt the user to change the setting by providing a link to the Windows 10 file system access and privacy article. Note that the user must close the app, toggle the setting, and restart the app. If they toggle the setting while the app is running, the platform will suspend your app so that you can save the state, then forcibly terminate the app in order to apply the new setting. In the April 2018 update, the default for the permission is On. In the October 2018 update, the default is Off.
More info

Get Users/Shared Folder in Mac using C#

Im trying to get the Users/Shared folder location in Mac so that i can write common user data(license) to it.I tried using
System.IO.Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.CommonApplicationData));
But its returning the folder in which I'm logged in.I know that i need to place the common application data in the Application Support folder but i think root privilege is required for this.If there is a better way to write to that folder,please suggest.
UPDATE:
I tried doing
File.Copy ("myfile.rtf", "Users//Shared//ll.txt");
But i get this exception >> Destination directory not found: Users/Shared

In OS X the directory is simply /Users/Shared, and it's directly off the root of the volume. There's no need to do Environment.GetFolderPath...
If you want to have user data or application data that can be shared by multiple users (read+write) you'll either want to create your own directory:
/Users/Shared/MyApp
and/or you can use:
/Users/Shared/Library/Application Support/MyApp
This way your application can share user data and application settings with all users. The /Library/Application Support folder (not to be confused with the one shared one), is owned by the system and anything that needs to write to it must obtain permission. The contents are read only, even for admin level users — something you'll want to consider when deciding where to store shared application data.

how to create sqlite database in windows store app located at a specific folder

Need help, I can't seem to access any other .sqlite database if its not located in the apps localfolder. Every tutorial I look at they always use
Path.Combine(Windows.Storage.ApplicationData.Current.LocalFolder.Path, "Example.sqlite");
I tried this:
const string testing = #"C:\Users\***\AppData\Local\Packages\*************\LocalState";
this.DBPath = Path.Combine(testing, "Example.sqlite");
using (var db = new SQLite.SQLiteConnection(this.DBPath))
{
db.CreateTable<Customer>();
}
and it worked. but when I change it to:
const string testing = #"C:\Databases";
It can't open the database even if I copied the database from the local folder of the app.
Any suggestions ? I'm still trying to learn.

You can't access the C: drive for windows store apps. It's part of the store's sandbox. Each app is limited to which files and folders can be viewed. If you have a local database file you need to access, define the file as content in your app and access it using the path "ms-appx:///..."

use file picker to select which folder you want to save the db file.
refer this article:
http://msdn.microsoft.com/en-us/library/windows/apps/hh967755.aspx?cs-save-lang=1&cs-lang=csharp#code-snippet-1

C# Windows Store BackgroundDownloader to removable storage

I am working on an app that will run on all Windows 8 devices (RT support a must) and I am working on adding some offline capabilities, but I can't figure out how to download to a removable storage device such as a USB drive or, in the case of a Surface RT, the micro SD card. Ideally I would like to be able to have the user specify the directory, but it may end up downloading hundreds of files so it has to be specified just once, not once per file. I also want to avoid requiring the user to manually configure libraries.
I have found plenty of articles about how to download to the various libraries, but those go to the internal storage and thus has very limited space on a Surface RT. How can I have the user specify a location for a large number of files to download and/or download to a removable storage device?
A really slick solution would be a way to programmatically create a library in a location of the user's choosing so the user can choose if they want it on the local system or on a removable device.
I appreciate any suggestions.

You should take advantage of FutureAccessList. It allows you to reuse files and folders that the user has previously granted you access to.
First the user will select the target folder using a FolderPicker:
var picker = new FolderPicker();
picker.FileTypeFilter.Add("*");
var folder = await picker.PickSingleFolderAsync();
You then add the folder to FutureAccessList and get back a string token which you can store for later use (e.g. to ApplicationData.LocalSettings):
var token = StorageApplicationPermissions.FutureAccessList.Add(folder);
When you want to download a file, first get the folder from FutureAccessList and create the target file:
var folder = await StorageApplicationPermissions.FutureAccessList
.GetFolderAsync(token);
var file = await folder.CreateFileAsync(filename);
With that data you can create a DownloadOperation:
var downloader = new BackgroundDownloader();
var download = downloader.CreateDownload(uri, file);
From here on proceed as if you were downloading to any other location (start the download, monitor progress...).