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";
if (Screen.ScreenControls[labelName] is ControlLabel label)
{
    label.Text = (tvq.Value as string) ?? "";
}
else
{
    // Handle the case where the control is not of type ControlLabel
    throw new InvalidCastException($"The control with name '{labelName}' is not of type ControlLabel.");
}