.NET - Check if directory is accessible without exception handling

Question

I need to go through various directories on the computer (via DirectoryInfo). Some of them aren't accessible, and UnauthorizedAccessException occurs. How can I check directory access without catching the exception?

Answer 1

You need to use the Security namespace.

See this SO answer.

From the answers:

FileIOPermission writePermission = new FileIOPermission(FileIOPermissionAccess.Write, filename);
if(!SecurityManager.IsGranted(writePermission))
{
  //No permission. 
  //Either throw an exception so this can be handled by a calling function
  //or inform the user that they do not have permission to write to the folder and return.
}

Update: (following comments)

FileIOPermission deals with security policies not filesystem permissions, so you need to use DirectoryInfo.GetAccessControl.

Answer 2

Simply put you can't. There is no way to check if a directory is accessible, all you can determine is that it was accessible. The reason why is as soon as the check completes the permissions can changed and invalidate your check. The most reliable strategy you can implement is to access the directories and catch the UnauthorizedAccessException.

I wrote a blog article on this subject recently which goes into a bit of detail here

• http://blogs.msdn.com/jaredpar/archive/2009/12/10/the-file-system-is-unpredictable.aspx