private void addVariableMenuItem_Click(object sender, System.EventArgs e)
        {
            if (upnpService == null) return;

            StateVariableEditForm stateVariableEditForm = new StateVariableEditForm(upnpService);
            DialogResult r = stateVariableEditForm.ShowDialog(this);
            if (r == DialogResult.OK)
            {
                UPnPStateVariable var = stateVariableEditForm.StateVariable;
                if (var != null)
                {
                    upnpService.AddStateVariable(var);
                    updateUserInterface();
                }
            }
        }
        private void stateVariableListView_DoubleClick(object sender, System.EventArgs e)
        {
            if (upnpService == null) return;

            if (stateVariableListView.SelectedItems.Count == 1)
            {
                UPnPStateVariable var = (UPnPStateVariable)stateVariableListView.SelectedItems[0].Tag;
                StateVariableEditForm stateVariableEditForm = new StateVariableEditForm();
                stateVariableEditForm.StateVariable = var;
                DialogResult r = stateVariableEditForm.ShowDialog(this);
                if (r == DialogResult.OK)
                {
                    if(var.Name==stateVariableEditForm.StateVariable.Name)
                    {
                        upnpService.AddStateVariable(stateVariableEditForm.StateVariable);
                    }
                    else
                    {
                        try
                        {
                            upnpService.RemoveStateVariable(var);
                            upnpService.AddStateVariable(stateVariableEditForm.StateVariable);
                        }
                        catch(UPnPStateVariable.CannotRemoveException)
                        {
                            MessageBox.Show("You cannot remove this State variable because it is associated with an existing action");
                            return;
                        }
                    }
                    updateUserInterface();
                }
            }
        }