Re: [delphi-en] Re: How to implement drag drop in VCL controls?

[Martin Wynne]

Hi TFE,

Here you go, use the OnMouseDown and OnMouseMove events for the TImage or 
whatever:

(can no doubt be much improved, dredged up from some old code, not checked)
-------------------

var
 control_mousedown_X,control_mousedown_Y:integer;

//_______________________________________________

procedure my_form.my_controlMouseDown(Sender: TObject; Button: TMouseButton; 
Shift: TShiftState; X, Y: Integer);

var
  mousedown_p,control_p:TPoint;
  
begin
  if GetCursorPos(mousedown_p)=False then begin mousedown_p.X:=0; 
mousedown_p.Y:=0; end; // mouse position in screen co-ords.

  control_p.X:= my_control.Left;
  control_p.Y:= my_control.Top;

  control_mousedown_X:=mousedown_p.X-(my_form.ClientToScreen(control_p)).X;  // 
mouse offset within the control
  control_mousedown_Y:=mousedown_p.Y-(my_form.ClientToScreen(control_p)).Y;

end;
//_______________________________________________

procedure Tmy_form.my_controlMouseMove(Sender: TObject; Shift: TShiftState; X, 
Y: Integer);

var
  mps:TPoint;

begin
  if Shift=[ssLeft]   // mouse down, dragging?
     then begin
            if GetCursorPos(mps)=False then begin mps.X:=0; mps.Y:=0; end;

            with my_control do begin
              Left:=(my_form.ScreenToClient(mps)).X-control_mousedown_X;
              Top:=(my_form.ScreenToClient(mps)).Y-control_mousedown_Y;
            end;//with
          
          end;
end;
//______________________________________________

regards,

Martin.