TextBox not firing valueChangedEvent in GWT

Question

I have this code and do action is never fired

  TextBox textbox = new TextBox();
    textbox .addValueChangeHandler(new ValueChangeHandler<String>() {
                @Override
                public void onValueChange(ValueChangeEvent<String> event) {
                    //do action
                }

            });

what am I doing wrong ?

One information a forgot the textBox was setEnable(true), is for this reason i don't use other handler. I find a solution the way to fire the event is when the textBox was set and for that i use coutTotal.setText("someText") but for fire the event i need to use coutTotal.setValue("sometext", true)

private void computeTotal() {
            Double total = 0.0;
            for (int i = 0; i < discloserPanel.getWidgetCount(); i++) {
                if (discloserPanel.getWidget(i) instanceof LigneCout) {
                    LigneCout ligneCout = (LigneCout) discloserPanel.getWidget(i);
                    total += ligneCout.getSousTotal();
                }
            }
            coutTotal.setValue(FormHelper.prepareDoubleForForm(total, 0), true);
        }