thanks for the answer. I was stopped with this.

"MISSING A callback handler is also needed for the X button when you close the dialog otherwise it never closes and remains in the background." I tried the attached code to solve this, but without success. The code execution doesn't stop.. Thanks

-- window_callbacks.ads

with Gtkada.Builder; use Gtkada.Builder;

package Window_Callbacks is
  function On_Window1_Delete_Event (Builder : access Gtkada_Builder_Record'Class) return Boolean;
  procedure On_File1_File_Set (Builder : access Gtkada_Builder_Record'Class);
end Window_Callbacks;



-- window_callbacks.adb

-- units from GtkAda
with Gtk.Main;

-- units from GtkAda
with Gtk.File_Chooser;           use Gtk.File_Chooser;
with Gtk.File_Chooser_Button;    use Gtk.File_Chooser_Button;

with Gtkada.File_Selection;      use Gtkada.File_Selection;


-- units from Glib
with Glib;              use Glib;
with Glib.Object;       use Glib.Object;

-- Ada predefined units
with Ada.Text_IO;            use Ada.Text_IO;
with Ada.Characters.Latin_1; use Ada.Characters.Latin_1;
with Ada.Exceptions;

package body Window_Callbacks  is

  -----------------------------------------------
  -- On_Window1_Delete_Event
  -----------------------------------------------
  function On_Window1_Delete_Event 
                 (Builder : access Gtkada_Builder_Record'Class) return Boolean is
    pragma Unreferenced (Builder);
    begin
      Gtk.Main.Main_Quit;
      return False;
    end On_Window1_Delete_Event;

  ---------------------------------
  -- On_File1_File_Set  --
  ---------------------------------
  procedure On_File1_File_Set (Builder : access Gtkada_Builder_Record'Class) is
                                                      
    Button : access Gtk_File_Chooser_Button_Record;

    function Name_Strict (File_Name : string) return string is
      I : natural := File_Name'Last; 
      begin
        loop
          exit when File_Name (I) = Solidus or File_Name (I) = Reverse_Solidus or I = File_Name'First;
            I := @ - 1;
        end loop;
        if File_Name (I) = Solidus or File_Name (I) = Reverse_Solidus then 
            return File_Name (I+1..File_Name'Last); --folder is present
          else
            return File_Name;     -- folder is absent
        end if;
      end; 

    begin
      -- Get the file chooser button
      Button := Gtk_File_Chooser_Button (Get_Object(Builder, "file1"));

      -- Get the filename
      declare
        File_Name   : constant string := Get_FileName (Button);
        Folder_Name : constant string := Get_Current_Folder (Button);
        begin
          Ada.Text_IO.Put_Line ("File selected : "    & File_Name);
          Ada.Text_IO.Put_Line ("Current Folder : "   & Folder_Name);
          Ada.Text_IO.Put_Line ("Strict File Name : " & Name_Strict (File_Name));
          New_line;
        end;

    end On_File1_File_Set;

end Window_Callbacks;



-- Glade_8

-- units from Gtk
with Gtk.Main;
with Glib.Error;     use Glib.Error;
with Gtk.Widget;     use Gtk.Widget;
with Gtk.Builder;    use Gtk.Builder;
with Gtkada.Builder; use Gtkada.Builder;

-- Ada predefined units
with Ada.Text_IO;       use Ada.Text_IO;

-- Application specific units
with Window_Callbacks; use Window_Callbacks;

procedure Glade_8 is

  Mon_Interface   : Constant String :=
    "<?xml version=""1.0"" encoding=""UTF-8""?>"
  & "<!-- Generated with glade 3.40.0 -->"
  & "<interface>"
  & "  <requires lib=""gtk+"" version=""3.20""/>"
  & "  <object class=""GtkAdjustment"" id=""adjustment1"">"
  & "    <property name=""upper"">100</property>"
  & "    <property name=""step-increment"">1</property>"
  & "    <property name=""page-increment"">10</property>"
  & "  </object>"
  & "  <object class=""GtkListStore"" id=""liststore1"">"
  & "    <columns>"
  & "      <!-- column-name gchararray1 -->"
  & "      <column type=""gchararray""/>"
  & "    </columns>"
  & "    <data>"
  & "      <row>"
  & "        <col id=""0"" translatable=""yes"">test1</col>"
  & "      </row>"
  & "      <row>"
  & "        <col id=""0"" translatable=""yes"">test2</col>"
  & "      </row>"
  & "      <row>"
  & "        <col id=""0"" translatable=""yes"">test3</col>"
  & "      </row>"
  & "    </data>"
  & "  </object>"
  & "  <object class=""GtkWindow"" id=""window"">"
  & "    <property name=""can-focus"">False</property>"
  & "    <child>"
  & "      <object class=""GtkFixed"" id=""fixed1"">"
  & "        <property name=""visible"">True</property>"
  & "        <property name=""can-focus"">False</property>"
  & "        <child>"
  & "          <object class=""GtkFileChooserButton"" id=""file1"">"
  & "            <property name=""width-request"">196</property>"
  & "            <property name=""visible"">True</property>"
  & "            <property name=""can-focus"">False</property>"
  & "            <property name=""title"" translatable=""yes""/>"
  & "            <signal name=""file-set"" handler=""on_file1_file_set"" swapped=""no""/>"
  & "          </object>"
  & "          <packing>"
  & "            <property name=""x"">9</property>"
  & "            <property name=""y"">234</property>"
  & "          </packing>"
  & "        </child>"
  & "      </object>"
  & "    </child>"
  & "  </object>"
  & "</interface>";
  
  Builder       : Gtkada_Builder;
  Error         : aliased Glib.Error.GError;
  use type Glib.Guint;
     
  begin
    Gtk.Main.Init;

    -- Etape 1 : créer un Builder
    Gtk_New (Builder);
    
    if Add_From_String (Gtk_Builder(Builder), Mon_Interface, Error'Access) = 0 then
      Put_Line ("Error : " & Get_Message (Error));
      Error_Free (Error);
      return;
    end if;
   
    -- Etape 2 : créer les handlers des events
    Register_Handler (Builder, "on_window1_delete_event", On_Window1_Delete_Event'Access);
    Register_Handler (Builder, "on_file1_file_set", On_File1_File_Set'Access);

    -- Etape 3 : Do_Connect connecte tous les handlers enregistrés en une fois.
    Do_Connect (Builder);

    -- Etape 4 : Afficher la fenetre avec ses dépendances
    Show_All (Gtk_Widget (Get_Object (GTK_Builder (Builder), "window")));

    -- Etape 5 : Lancer la boucle infinie.
    Gtk.Main.Main;

    -- Etape 6 : Unref pour libérer la memoire associée au Builder.
    Unref (Builder);

  end Glade_8;