SaveFileDialog exception in my WPF app

Question

One of my customers is experiencing a crash in my WPF application when saving a file.

My save file code is:

var saveFileDialog = new SaveFileDialog {
  InitialDirectory = string.Concat(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), @"\MyApp"),
  FileName = "MyFile", 
  OverwritePrompt = true,
  AddExtension = true
};

if (saveFileDialog.ShowDialog() == true) {
  ...
}

And here is the exception they are getting:

Value does not fall within the expected range.

A System.ArgumentException occurred
   at MS.Internal.Interop.HRESULT.ThrowIfFailed(String message)
   at MS.Internal.AppModel.ShellUtil.GetShellItemForPath(String path)
   at Microsoft.Win32.FileDialog.PrepareVistaDialog(IFileDialog dialog)
   at Microsoft.Win32.FileDialog.RunVistaDialog(IntPtr hwndOwner)
   at Microsoft.Win32.FileDialog.RunDialog(IntPtr hwndOwner)
   at Microsoft.Win32.CommonDialog.ShowDialog()

(Where the ShowDialog in the last line refers to the call I make in my code above.)

So my hunch is that in my customer's case, the call to Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) is returning something that the SaveFileDialog does not like as the InitialDirectory. I've found in web searches (and validated) that this error occurs when passing a relative path as the InitialDirectory of the SaveFileDialog. Is it possible that Environment.SpecialFolder.MyDocuments could be returned as a relative path? If not, does anybody know another potentially invalid format? Could a certain SpecialFolder.MyDocuments network path be the cause? Any other ideas?

I don't have direct access to my customer's machine and they aren't particularly tech savvy so it's not possible to be 100% certain what is happening.

Answer 1

Found it.

InitialDirectory = string.Concat(
    Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments),
    @"\MyApp"
)

Environment.SpecialFolder.MyDocuments was being returned on my customer's machine with a trailing '\' character, and so the complete concatenated path had a double '\' in it.

SaveFileDialog crashes when you pass an InitialDirectory path containing a double '\' (which is a flaw in my opinion - it should more gracefully handle or coerce invalid inputs).

I use the Path.Combine static method instead now to handle both variants:

InitialDirectory = Path.Combine(
    Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments),
    "MyApp"
)

And it crashes no more.