public void Open(File file)
 {
     if (file is Back) {
         Return(ParentFolder);
         return;
     }
     ParentFolder = (Directory)file;
 }
 public bool CanOpen(File file)
 {
     return file is Directory || file is Back;
 }
 public bool CanViewFile(File file)
 {
     return file.GetType() == typeof(File);
 }
 public void ViewFile(File file)
 {
     var document = DocumentManagerService.CreateDocument("FileView", file.Path, this);
     if (document != null) {
         document.Title = file.Path;
         document.Show();
     }
 }