c:\users\public folder not accessible from metro apps on x86 machines - windows-store-apps

Question

I am not able to access C:\Users\Public\Documents folder from Windows store app running on a x86 machine using StorageFolder.GetFolderFromPathAsync("C:\Users\Public\Documents"). It works fine on my win8 desktop. any idea why I get this error?
Thanks,
MetroUI.

Answer 1

You can't access the file system outside your apps sandbox using that method. That will only access files in your apps isolated storage.
If you want to get files from outside the sandbox you will have to use a FileOpenPicker and have the user select the file
var picker = new FileOpenPicker();
picker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
var file = await picker.PickSingleFileAsync();
if (file != null)
{
IRandomAccessStream stream = await file.OpenAsync(Windows.Storage.FileAccessMode.Read);
}
Then you would work with the data in the stream.

Answer 2

J.B is right, you can't access that folder directly due to sandbox limitations, but there are 2 other approaches you can take that might suite you better.
If you Add Documents Library to your app's Capabilities, you will be able to access the files in user's Documents library directly (it should include Public Documents as well, unless the user changed his settings), as long as you have declared a File Type Association for that extension to your app's Declarations. You can set both by editing Package.appxmanifest. Use the following code to access the StorageFolder:
var folder = KnownFolders.DocumentsLibrary;
Keep in mind that you need a company account to publish apps with Documents Library capability to Windows Store.
Alternatively you can use FolderPicker so that the user will grant you access to that folder. In this case you don't need any capabilities or declarations and you will be able to access all files:
var picker = new FolderPicker();
picker.FileTypeFilter.Add(".txt");
var folder = await picker.PickSingleFolderAsync();
You don't need the user to select the folder every time the app starts. You can store its reference to FutureAccessList to access it later and store the corresponding token (e.g. to settings):
var token = StorageApplicationPermissions.FutureAccessList.Add(folder);
When you want to access the folder again just use the token to get the folder reference:
folder = await StorageApplicationPermissions.FutureAccessList.GetFolderAsync(token);
var items = await folder.GetItemsAsync();