In this example:
Program project1; uses Windows, messages; {custom process for wm_close message call} procedure onclose (H: hwnd); begin if idok = MessageBox (H, 'Are you sure you want to disable it? ',' Hint ', mb_okcancel) Then destroywindow (h); end; function wndproc (WND: hwnd; MSG: uint; wparam: integer; lparam: integer): integer; stdcall; begin result: = 0; Case MSG of wm_close: onclose (WND); {call the custom onclose process when receiving the wm_close message} wm_destroy: postquitmessage (0); else result: = defwindowproc (WND, MSG, wparam, lparam); end; function regmywndclass: Boolean; var CLS: twndclass; begin Cls. style: = cs_hredraw or cs_vredraw; Cls. lpfnwndproc: = @ wndproc; Cls. cbclsextra: = 0; Cls. cbwndextra: = 0; Cls. hinstance: = hinstance; Cls. hicon: = 0; Cls. hcursor: = loadcursor (0, idc_arrow); Cls. hbrbackground: = hbrush (color_window + 1); Cls. lpszmenuname: = nil; Cls. lpszclassname: = 'mywnd'; Result: = registerclass (CLS) 0; end ;{Program Entry} const tit = 'new form'; Ws = ws_overlappedwindow; X = 100; y = 100; W = 300; H = 180; var hwnd: thandle; MSG: tmsg; begin regmywndclass; hwnd: = createwindow ('mywnd', tit, WS, X, Y, W, H, 0, 0, hinstance, nil); showwindow (hwnd, sw_shownormal ); updatewindow (hwnd); While (getmessage (MSG, 0, 0, 0) do begin translatemessage (MSG); dispatchmessage (MSG); end.