function call user control based on the parent pag

Don't. Instead, do it the other way: create an event in your child form, which the parent form subscribes to. That way, the child does not need to know anything about the existence of the parent - it just signals "I have data!" and the parent will process it as required if it is interested.


In the child form:

public partial class frmChild : Form
   {
   // Signal data change happened
   public event EventHandler Changed;

   protected virtual void OnChanged(EventArgs e)
      {
      EventHandler eh = Changed;
      if (eh != null)
         {
         eh(this, e);
         }
      }

   private void DoSomethingToChangeData()
      {
      OnChanged(null);
      }
   }

----- The asign to eh is in case the handler changes between null check
----- and exec.
----- (unlikely, but possible)

----- The null check is to ensure there is a handler. If not, better to
----- ignore it gracefully, than to rely on the thrown exception
----- (NullReferenceException)

In the Parent form:

private void ShowChildForm()
    {
    // Link in his event so if it changes, we detect it.
    frmChild fd = new frmChild();
    fd.Change += new frmChange.ChangeHandler(Changed);
    fd.ShowDialog();
    }

//
// Fired when the data is changed at a lower level.
//
private void Changed(object sender, EventArgs e)
    {
    }