Showing 'This folder is empty' background when my shell extension folder is empty

Question

In my shell extension, I want to mimic explorer's behavior and show 'This folder is empty' message when in fact my folder is empty:

However, I can't accomplish it.

Using API Monitor, I see that when explorer refreshes an empty folder, IEnumIDList::Next() is returning the following:

Meaning, that the 'next' item returned is NULL, the number of items is 0 and the result is S_FALSE.

As mentioned, I tried to mimic the return values, and indeed no items are loaded for the folder, but no message appear either.

So what API would trigger this message?

Answer 1

Your IEnumIDList implementation must implement IObjectWithSite. Sample of implementation:

  var
    ServiceProvider: IServiceProvider;
    ShellBrowser: IShellBrowser;
    ShellView: IShellView;
    FolderView2: IFolderView2;
  begin
    if not Assigned(ASite) then Exit;
    OleCheck(ASite.QueryInterface(IServiceProvider, ServiceProvider));
    try
      OleCheck(ServiceProvider.QueryService(SID_STopLevelBrowser, IShellBrowser, ShellBrowser));
      try
        OleCheck(ShellBrowser.QueryActiveShellView(ShellView));
        try
          OleCheck(ShellView.QueryInterface(IFolderView2, FolderView2));
          try
            FolderView2.SetText(FVST_EMPTYTEXT, 'The message you want to see');
          finally
            FolderView2 := nil;
          end;
        finally
          ShellView := nil;
        end;
      finally
        ShellBrowser := nil;
      end;
    finally
      ServiceProvider := nil;
    end;
  end;

Result:

Also you can use the same code in your IShellFolder implementation.