获取窗体外鼠标点击事件,为什么我用钩子也获取不到?

ShowModal后 要获取鼠标在窗体外地点击事件,
看网上说用钩子,可是也是获取不了procedure TForm2.FormCreate(Sender: TObject);
begin
YourHook:=SetWindowsHookEx(WH_MOUSE,@HookProc,0,GetCurrentThreadID);
end;
function HookProc(nCode:Integer;WParam: WPARAM;LParam:LPARAM):LRESULT;stdcall;
var
   r: TRect;
   p: TPoint;
begin
  Result := HC_ACTION;
   if nCode < 0 then Result := CallNextHookEx(YourHook, nCode, wParam, lParam);
  if wParam = WM_LBUTTONDOWN then
  begin
    form2.Memo1.Lines.Add('WM_LBUTTONDOWN');//为什么这边获取不到
  end
  else
Result := CallNextHookEx(YourHook, nCode, wParam, lParam);
end;