Lablgtk motion_notify event doesn't work

I want to implement drawing area that responds with some action when the mouse click within area. So i connected to motion_notify event, but nothing happen when mouse button is clicked. Here is example code:

File graph.ml

open GObj
class gridViewCanvas ?width ?height ?packing ?show rows cols =

  let vbox = GPack.vbox ?width ?height ?packing ?show () in

  let da = GMisc.drawing_area ~packing:vbox#add () in
  let drawable = lazy (new GDraw.drawable da#misc#window) in

  object (self)
    inherit widget vbox#as_widget

    initializer
      ignore(da#event#connect#expose
          ~callback: (fun _ -> self#repaint (); false));
      ignore(da#event#connect#motion_notify
          ~callback: (fun _ -> prerr_endline "OK"; false))

    method private drawGrid drawable =
      let (width, height) = drawable#size in
      let cellWidth = float_of_int width /. float_of_int cols in
      let cellHeight = float_of_int height /. float_of_int rows in

      drawable#set_foreground `BLACK;
      let currHeight : float ref = ref 0. in
      for i = 0 to rows - 1 do
        drawable#line ~x: 0 ~y: (int_of_float !currHeight)
                      ~x: width ~y: (int_of_float !currHeight);
        currHeight := !currHeight +. cellHeight;
      done;

      let currWidth : float ref = ref 0. in
      for i = 0 to cols - 1 do
        drawable#line ~x: (int_of_float !currWidth) ~y: 0
                      ~x: (int_of_float !currWidth) ~y: height;
        currWidth := !currWidth +. cellWidth;
      done;
      ()

    method private repaint () =
     let drawable = Lazy.force drawable in
     let (width, height) = drawable#size in
     drawable#set_foreground `WHITE;
     drawable#rectangle ~x:0 ~y:0 ~width ~height ~filled:true ();

     self#drawGrid drawable
end

File test.ml

open GMain
open GdkKeysyms
open Graph

let locale = GtkMain.Main.init ()

let main () =
  let window = GWindow.window ~width:640 ~height:480
                          ~title:"Title" () in
  let vbox = GPack.vbox ~packing:window#add () in
  window#connect#destroy ~callback:Main.quit;

  let menubar = GMenu.menu_bar ~packing:vbox#pack () in
  let factory = new GMenu.factory menubar in
  let accel_group = factory#accel_group in
  let file_menu = factory#add_submenu "File" in

  let factory = new GMenu.factory file_menu ~accel_group in
  factory#add_item "Quit" ~key:_Q ~callback: Main.quit;

  let graph = new gridViewCanvas ~packing:vbox#add 5 3 in

  window#show ();
  Main.main ()

let () =
  main ()

compiling with
ocamlfind ocamlc -g -package lablgtk2 -linkpkg graph.ml test.ml -o graphtest

Any idea what I'm doing wrong?

This is because the sensitivity of your widget to events is not set. Your widget will come to live if you add the following line after the initializer clause :

            da#event#add[`ALL_EVENTS];

Much more events are available, and you provide the list of the events to which your widget will be sensitive.