How to execute my custom action when right-clicking on a TMemo control?

In a Delphi 10.4.2 32-bit VCL Application, I need to do different actions when the user (left- or right-)clicks on a TMemo control (which is in ReadOnly mode):

procedure TForm1.Memo1MouseDown(Sender: TObject; Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbLeft then
    DoAction1
  else if Button = mbRight then
    DoAction2;
end;

DoAction2 consists of invoking a specific dialog.

However, when I right-click on the Memo control, the native context menu of the TMemo control shows up, and DoAction2 is not executed:

I have tried to deactivate the right-click context menu of the Memo control with this code:

Memo1.OnContextPopup := nil;

But it does not work: The context menu still shows up when right-clicking the Memo control.

So how can I deactivate the native context menu and execute my action when right-clicking on the Memo control?

This is easy.

Your code Memo1.OnContextPopup := nil; has no effect because the Memo1.OnContextPopup property already is nil, as you can see in the Object Inspector; that is, by default you have no custom handler.

What you need to do is to add such a custom handler and set the Handled var property to True. At design time, use the Object Inspector to create an OnContextPopup handler for your memo, with the following code:

procedure TForm1.Memo1ContextPopup(Sender: TObject; MousePos: TPoint;
  var Handled: Boolean);
begin
  Handled := True;
end;

Now the default context menu is suppressed and you can try, for example,

procedure TForm1.Memo1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Button = mbLeft then
    Winapi.Windows.Beep(300, 250)
  else if Button = mbRight then
    Winapi.Windows.Beep(300, 1000);
end;