--- a/libgui/src/qt-interpreter-events.h	Fri Sep 17 12:46:59 2021 -0700
+++ b/libgui/src/qt-interpreter-events.h	Sun Sep 19 15:36:19 2021 +0200
@@ -86,6 +86,8 @@
     void start_gui (bool gui_app = false);
     void close_gui (void);
 
+    bool have_dialogs (void) const { return true; }
+
     std::list<std::string>
     file_dialog (const filter_list& filter, const std::string& title,
                  const std::string& filename, const std::string& pathname,

--- a/libinterp/corefcn/event-manager.cc	Fri Sep 17 12:46:59 2021 -0700
+++ b/libinterp/corefcn/event-manager.cc	Sun Sep 19 15:36:19 2021 +0200
@@ -234,6 +234,17 @@
   return ovl (evmgr.enabled ());
 }
 
+DEFMETHOD (__event_manager_have_dialogs__, interp, , ,
+           doc: /* -*- texinfo -*-
+@deftypefn {} {} __event_manager_have_dialogs__ ()
+Undocumented internal function.
+@end deftypefn */)
+{
+  event_manager& evmgr = interp.get_event_manager ();
+
+  return ovl (evmgr.have_dialogs ());
+}
+
 DEFMETHOD (__event_manager_edit_file__, interp, args, ,
            doc: /* -*- texinfo -*-
 @deftypefn {} {} __event_manager_edit_file__ (@var{file})

--- a/libinterp/corefcn/event-manager.h	Fri Sep 17 12:46:59 2021 -0700
+++ b/libinterp/corefcn/event-manager.h	Sun Sep 19 15:36:19 2021 +0200
@@ -100,6 +100,8 @@
 
     // Dialogs.
 
+    virtual bool have_dialogs (void) const { return false; }
+
     typedef std::list<std::pair<std::string, std::string>> filter_list;
 
     virtual std::list<std::string>
@@ -378,6 +380,13 @@
         m_instance->close_gui ();
     }
 
+    // Dialogs
+
+    bool have_dialogs (void) const
+    {
+      return m_qt_event_handlers && m_qt_event_handlers->have_dialogs ();
+    }
+
     typedef std::list<std::pair<std::string, std::string>> filter_list;
 
     std::list<std::string>
@@ -385,7 +394,7 @@
                  const std::string& filename, const std::string& dirname,
                  const std::string& multimode)
     {
-      return (enabled ()
+      return (enabled () && have_dialogs ()
               ? m_instance->file_dialog (filter, title, filename, dirname,
                                          multimode)
               : std::list<std::string> ());
@@ -398,7 +407,7 @@
                   const std::list<float>& nc,
                   const std::list<std::string>& defaults)
     {
-      return (enabled ()
+      return (enabled () && have_dialogs ()
               ? m_instance->input_dialog (prompt, title, nr, nc, defaults)
               : std::list<std::string> ());
     }
@@ -413,7 +422,7 @@
                  const std::string& ok_string,
                  const std::string& cancel_string)
     {
-      return (enabled ()
+      return (enabled () && have_dialogs ()
               ? m_instance->list_dialog (list, mode, width, height,
                                          initial_value, name, prompt,
                                          ok_string, cancel_string)
@@ -425,7 +434,7 @@
                      const std::string& btn1, const std::string& btn2,
                      const std::string& btn3, const std::string& btndef)
     {
-      return (enabled ()
+      return (enabled () && have_dialogs ()
               ? m_instance->question_dialog (msg, title, btn1,
                                              btn2, btn3, btndef)
               : "");

--- a/scripts/gui/inputdlg.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/inputdlg.m	Sun Sep 19 15:36:19 2021 +0200
@@ -163,7 +163,7 @@
   ## convert numeric values in defaults cell array to strings
   defs = cellfun (@num2str, defaults, "UniformOutput", false);
 
-  if (__event_manager_enabled__ ())
+  if (__event_manager_have_dialogs__ ())
     cstr = __event_manager_input_dialog__ (prompt, title, rowscols, defs);
   else
     error ("inputdlg is not available in this version of Octave");

--- a/scripts/gui/listdlg.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/listdlg.m	Sun Sep 19 15:36:19 2021 +0200
@@ -154,13 +154,13 @@
     error ('listdlg: "SelectionMode" must be "single" or "multiple"');
   endif
 
-  if (! __event_manager_enabled__ ())
+  if (! __event_manager_have_dialogs__ ())
     error ("listdlg is not available in this version of Octave");
   endif
 
   [sel, ok] = __event_manager_list_dialog__ (listcell, selmode, listsize,
-                                           initialvalue, name, prompt,
-                                           okstring, cancelstring);
+                                             initialvalue, name, prompt,
+                                             okstring, cancelstring);
 
 endfunction
 

--- a/scripts/gui/msgbox.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/msgbox.m	Sun Sep 19 15:36:19 2021 +0200
@@ -173,7 +173,7 @@
   endif
 
   ## Make a GUI element or print to console
-  if (__event_manager_enabled__ ())
+  if (__event_manager_have_dialogs__ ())
     retval = __msgbox__ (msg, tit, icon, windowstyle, interpreter);
   else
     if (iscellstr (msg))

--- a/scripts/gui/private/__get_funcname__.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/private/__get_funcname__.m	Sun Sep 19 15:36:19 2021 +0200
@@ -33,7 +33,7 @@
 
 function funcname = __get_funcname__ (basename)
 
-  if (! __event_manager_enabled__ ())
+  if (! __event_manager_enabled__ () || ! __event_manager_have_dialogs__ ())
     tk = graphics_toolkit ();
     funcname = [ "__" basename "_" tk "__"];
     if (numel (tk) > 0 && ! strcmp (tk, "fltk")

--- a/scripts/gui/questdlg.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/questdlg.m	Sun Sep 19 15:36:19 2021 +0200
@@ -124,9 +124,9 @@
 
   endswitch
 
-  if (__event_manager_enabled__ ())
+  if (__event_manager_have_dialogs__ ())
     btn = __event_manager_question_dialog__ (msg, title, options{1}, options{2},
-                                           options{3}, options{4});
+                                             options{3}, options{4});
   else
     error ("questdlg is not available in this version of Octave");
   endif

--- a/scripts/gui/uigetdir.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/uigetdir.m	Sun Sep 19 15:36:19 2021 +0200
@@ -49,7 +49,7 @@
     init_path = fileparts (init_path);
   endif
 
-  if (__event_manager_enabled__ ())
+  if (__event_manager_have_dialogs__ ())
     file_filter = cell (0, 2);
     default_file_name = "";
     dialog_position = [240, 120];
@@ -57,8 +57,8 @@
 
     [filename, dirname, filterindex] ...
       = __event_manager_file_dialog__ (file_filter, dialog_name,
-                                     default_file_name, dialog_position,
-                                     dialog_mode, init_path);
+                                       default_file_name, dialog_position,
+                                       dialog_mode, init_path);
   else
     funcname = __get_funcname__ (mfilename ());
     dirname = feval (funcname, init_path, dialog_name);

--- a/scripts/gui/uigetfile.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/uigetfile.m	Sun Sep 19 15:36:19 2021 +0200
@@ -183,7 +183,7 @@
     endfor
   endif
 
-  if (__event_manager_enabled__ ())
+  if (__event_manager_have_dialogs__ ())
     [retfile, retpath, retindex] = __event_manager_file_dialog__ (outargs{:});
   else
     funcname = __get_funcname__ (mfilename ());

--- a/scripts/gui/uiputfile.m	Fri Sep 17 12:46:59 2021 -0700
+++ b/scripts/gui/uiputfile.m	Sun Sep 19 15:36:19 2021 +0200
@@ -117,7 +117,7 @@
     endif
   endif
 
-  if (__event_manager_enabled__ ())
+  if (__event_manager_have_dialogs__ ())
     [retfile, retpath, retindex] = __event_manager_file_dialog__ (outargs{:});
   else
     funcname = __get_funcname__ (mfilename ());