OnValueChange

public void OnBeginValueChange(object sender, TagSubscriptionArgs subscription, TVQ tvq)
{
    //// control that value is being changed on
    // ControlBase control = sender as ControlBase;

    // NOTE: Event is triggered BEFORE control property has been changed.
    // Any modifications to the `tvq` argument will be applied to the control.
    double number;
    if (double.TryParse(tvq?.Value?.ToString() ?? "NaN", out number))
    {
        switch (number) {
            case 0:
                tvq.Value = "Off";
                return;
            case 1:
                tvq.Value = "On";
                return;
            default:
                tvq.Value = "Undefined";
                return;
        }
    }

    tvq.Value = "Error";
}

public void OnEndValueChange(object sender, TagSubscriptionArgs subscription, TVQ tvq)
{
    // control that value is being changed on
    ControlBase control = sender as ControlBase;

    // NOTE: Event is triggered AFTER control property has been changed.
    // Any modifications to the `tvq` argument will NOT be applied to the control.
    double number;
    if (double.TryParse(tvq?.Value?.ToString() ?? "NaN", out number))
    {
        switch (number) {
            case 0:
                tvq.Value = "Off";
                break;
            case 1:
                tvq.Value = "On";
                break;
            default:
                tvq.Value = "Undefined";
                break;
        }
    }
    else
    {
        tvq.Value = "Error";
    }

    // BAD CODE: since value of control has already been changed
    // we need to set the value explicitly which could cause an
    // infinite loop since the OnEndValueChange event gets fired
    // when the value is changed. Fortunately, Axiom prevents this
    // condition from getting stuck in an infinite loop, but it is
    // NOT RECOMMENDED to change the value of the control that
    // the event was triggered on in the OnEndValueChange event.
    control.Value = tvq;

    // GOOD CODE: if we want to change the value of a different
    // control based on the value of this control, we can do it
    // by getting a reference to that control and changing its
    // value. The following code assumes there is a control in
    // the current screen named "Label1".
    string labelName = "Label1";
    ControlLabel label = Screen.ScreenControls[labelName];
    label.Text = (tvq.Value as string) ?? "";
}