How to show a TPopupMenu when you click a TButton?

Question

I want to show a popupmenu when click a button, but this procedure has error in Delphi XE.

procedure ShowPopupMenuEx(var mb1:TMouseButton;var X:integer;var Y:integer;var pPopUP:TPopupMenu);
var
  popupPoint : TPoint;
begin
  if (mb1 = mbLeft) then begin
    popupPoint.X := x ;
    popupPoint.Y := y ;
    popupPoint := ClientToScreen(popupPoint);   //Error Here
    pPopUP.Popup(popupPoint.X, popupPoint.Y) ;   
  end;
end;

procedure TForm1.Button1MouseUp(Sender: TObject; Button: TMouseButton;Shift: TShiftState; X, Y: Integer);
begin
  ShowPopupMenuEx(button,Button1.Left,Button1.Top,PopupMenu1); //Error Here
end;

when click button show this error :

[DCC Error] Form1.pas(205): E2010 Incompatible types: 'HWND' and 'TPoint'
[DCC Error] Form1.pas(398): E2197 Constant object cannot be passed as var parameter
[DCC Error] Form1.pas(398): E2197 Constant object cannot be passed as var parameter

Is there any better way for show popupmenu, when click a button?

Answer 1

Just do

procedure TForm1.Button1Click(Sender: TObject);
var
  pnt: TPoint;
begin
  if GetCursorPos(pnt) then
    PopupMenu1.Popup(pnt.X, pnt.Y);
end;

Some more discussion

If you for some reason need to use OnMosuseUp, you can do

procedure TForm1.Button1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  pnt: TPoint;
begin
  if (Button = mbLeft) and GetCursorPos(pnt) then
    PopupMenu1.Popup(pnt.X, pnt.Y);
end;

Your code doesn't work because

1. ClientToScreen is a function of the Windows API with signature

   function ClientToScreen(hWnd: HWND; var lpPoint: TPoint): BOOL;
   

   But, there is also a TControl.ClientToScreen with signature

   function TControl.ClientToScreen(const Point: TPoint): TPoint;
   

   Hence, if you are in a class method, the class being a decendant of TControl, ClientToScreen will refer to the latter one. If not, it will refer to the former one. And this one, of course, needs to know which window we are to transform coordinates from!

2. Also, if you declare

   var mb1: TMouseButton
   

   as a parameter, then only a variable of type TMouseButton will be accepted. But I cannot see any reason why you would like this signature of your ShowPopupMenuEx function. In fact, I see no need for such a function at all...

An Alternative

My code above will popup the menu at the cursor pos. If you need to fix the point relative to one corner of the button, instead, you can do

// Popup at the top-left pixel of the button
procedure TForm1.Button1Click(Sender: TObject);
begin
  with Button1.ClientToScreen(point(0, 0)) do
    PopupMenu1.Popup(X, Y);
end;

// Popup at the bottom-right pixel of the button
procedure TForm1.Button1Click(Sender: TObject);
begin
  with Button1.ClientToScreen(point(Button1.Width, Button1.Height)) do
    PopupMenu1.Popup(X, Y);
end;

// Popup at the bottom-left pixel of the button
procedure TForm1.Button1Click(Sender: TObject);
begin
  with Button1.ClientToScreen(point(0, Button1.Height)) do
    PopupMenu1.Popup(X, Y);
end;