[Lazarus] controling a loop

[Schindler Karl-Michael]

Hi.
                                                                                                                                                                                                                                              
I want to control the execution of a loop with a checkbox. If the checkbox is checked the loop should run, if it is unchecked no action. I tried this with onClick:

CheckBox.Click(Sender:TObject);
begin
  repeat
    Some Action …
    Form.Update;
  until (CheckBox.State <> checked)
end;

The loop starts, but i cannot click the Checkbox again for switching off. How to do it? Is it possible without threads?

Michael.