Disable textbox required field validator control

I want to disable the requiredfield validator control for the textbox based on some condition of a variable:

if(var==null)
{
    //Activate it
}
else
{
开发者_Go百科    //disable it
}

What code do I need here?

if(var == null)
{
  requirefieldvalidator1.Enabled = true;
}
else
{
  requirefieldvalidator1.Enabled = false;
}