add a double-click event to the header of a Listview ？

{

 MS did not see fit to send a notification to the listview when the user

 Double - clicks on the header. But the header control class does have the

 CS_DBLCLKS Style, so it does get WM_LBUTTONDBLCLK messages, it just does

 not do anything with them. To get at these messages requires API - Style

 subclassing of the header control.

}

uses commctrl;

function HeaderProc(wnd: HWND; Msg: Cardinal; wParam: wParam; lParam: lParam): Longint;

 stdcall;

var

 hti: THDHitTestInfo;

begin

 Result := CallWindowProc(Pointer(GetWindowLong(wnd, GWL_USERDATA)),

   wnd, Msg, wParam, lParam);

 if Msg = WM_LBUTTONDBLCLK then

 begin

   FillChar(hti, SizeOf(hti), 0);

   hti.Point := SmallPointToPoint(TSmallPoint(lParam));

   if SendMessage(wnd, HDM_HITTEST, 0, Longint(@hti)) >= 0 then

     if hti.Flags = HHT_ONHEADER then

       // would usually send a custom notification to GetParent(wnd) here

       Form1.Memo1.Lines.Add(Format('doubleclick on header item %d', [hti.Item]));

 end;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

 wnd: HWND;

 buffer: array [0..80] of Char;

 oldProc: Integer;

begin

 wnd := GetWindow(Listview1.Handle, GW_CHILD);

 if wnd <> 0 then

 begin

   Windows.GetClassname(wnd, buffer, SizeOf(buffer));

   memo1.Text := buffer;

   if (GetClassLong(wnd, GCL_STYLE) and CS_DBLCLKS) <> 0 then

   begin

     Memo1.Lines.Add('Has doubleclicks style');

     oldproc := GetWIndowLong(wnd, GWL_WNDPROC);

     if GetWindowLong(wnd, GWL_USERDATA) <> 0 then

       raise Exception.Create('Cannot sublcass header, USERDATA already in use');

     SetWIndowLong(wnd, GWL_USERDATA, oldproc);

     SetWindowLong(wnd, GWL_WNDPROC, Integer(@HeaderProc));

   end;

 end

 else

   Memo1.Text := 'No child';

end;