Question

Problem accessing mp3 files in WinRT app.

‘System.UnauthorizedAccessException’ occurs when app tries to open a mp3 file by name in the same folder as a file returned by FileOpenPicker. Put another way, the user picks an info file in Documents with the same name as a mp3 file. App opens the info file just fine but cannot open the mp3 file.

For example: I have a pair of files (file1.info) and (file1.mp3). A filepicker allows selecting a (*.info) file.

The user selects (file1.info). The app then opens both (file1.info) and (file1.mp3). Both files reside in a DocumentsLibrary folder, but are NOT in the MusicLibrary. The problem is when I try to open (file1.mp3) I get the ‘UnauthorizedAccessException’.

To prepro the issue:

Files:
Copy an mp3 file to Documents.
Create a text file with the same base name as the mp3 file and change its extension to .info.

In Package.appxmanifest > Declarations add a ‘File Type Associations’ declaration. Check ‘Open is safe’. Add

supported file types ‘.mp3’ and ‘.info’. Leave ‘Content type’ empty.

Code:

Dim file as StorageFile
Dim fileopenpicker As FileOpenPicker
Dim infofile As StorageFile
Dim mp3file As StorageFile 
Dim filename As String
fileopenpicker = New FileOpenPicker()
fileopenpicker.FileTypeFilter.Add(".info")
fileopenpicker.FileTypeFilter.Add(".mp3")
fileopenpicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary
file = Await fileopenpicker.PickSingleFileAsync()
If file.Path.EndsWith(".info") Then
    infofile = file
    filename = file.Path.Substring(0, file.Path.Length - 4) & "mp3"
    ' This command fails with 'System.UnauthorizedAccessException'
    mp3file = Await StorageFile.GetFileFromPathAsync(filename)
Else 'file is an mp3 file
    mp3file = file
    filename = file.Path.Substring(0, file.Path.Length - 3) & "info"
    ' This command succeeds!
    infofile = Await StorageFile.GetFileFromPathAsync(filename)
End If

So it appears that there is some specific problem with opening an mp3 file when the file is not actually chosen by the fileopenpicker.

Answer 1

I checked this issue with an app that has the capability Documents Library and the filetypes .mp3 and .info declared. I figured out that it seems to be a very strange bug. If you pass the path to the documents library folder using an uppercase drive letter after having opened a FileOpenPicker you get an UnauthorizedAccessException. Using the path with a lowercase drive letter works. Strangely you can use an uppercase drive letter before having opened a FileOpenPicker.

So the workaround is to lowercase the path.

Here’s the code I used (C#):

// Trying to get some files from the documents library
// Note: F:\Program Data is my primary documents library folder
string mp3FilePath = @"F:\Program Data\2Mann1Maus.mp3";

// This works even if the drive letter is uppercase
StorageFile file1 = await StorageFile.GetFileFromPathAsync(mp3FilePath);

// It also works with a lowercase drive letter
string infoFilePath = @"f:\Program Data\2Mann1Maus.info";
StorageFile file2 = await StorageFile.GetFileFromPathAsync(infoFilePath);

FileOpenPicker fileopenpicker = new FileOpenPicker();
fileopenpicker.FileTypeFilter.Add(".info");
fileopenpicker.FileTypeFilter.Add(".mp3");
fileopenpicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
StorageFile file = await fileopenpicker.PickSingleFileAsync();
if (file.Path.EndsWith(".info"))
{
   string filename = file.Path.Substring(0, file.Path.Length - 4) + "mp3";   

   // This works
   string testFileName1 = filename.Substring(0, 1).ToLower() + 
      filename.Substring(1,  filename.Length - 1);
   StorageFile mp3file1 = await StorageFile.GetFileFromPathAsync(testFileName1);

   // This works as well
   string testFileName2 = filename.ToLower();
   StorageFile mp3file2 = await StorageFile.GetFileFromPathAsync(testFileName2); 

   // This does cause an UnauthorizedAccessException
   StorageFile mp3file3 = await StorageFile.GetFileFromPathAsync(filename);
}
else
{
   StorageFile mp3file = file;
   String filename = file.Path.Substring(0, file.Path.Length - 3) + "info"; 

   // This works
   string testFileName1 = filename.Substring(0, 1).ToLower() + 
      filename.Substring(1, filename.Length - 1);
   StorageFile infoFile1 = await StorageFile.GetFileFromPathAsync(testFileName1); 

   // This works as well
   string testFileName2 = filename.ToLower();
   StorageFile infoFile2 = await StorageFile.GetFileFromPathAsync(testFileName2); 

   // This does cause an UnauthorizedAccessException
   StorageFile infoFile3 = await StorageFile.GetFileFromPathAsync(filename);
}