private void onUserAdd(object sender, EventArgs e) { try { // does user belong to group ? foreach (object o in listboxUsers.Items) { DCUser user = o as DCUser; if (null != user && string.Equals(tbUserToAdd.Text, user.Name, StringComparison.CurrentCultureIgnoreCase)) { MessageBox.Show(string.Format("User '{0}' already member of group {1}!", user.Name)); return; } } PLMPackServiceClient client = WCFClientSingleton.Instance.Client; // does user exist if (!client.UserExists(tbUserToAdd.Text)) { MessageBox.Show(string.Format("User '{0}' does not exist!")); return; } // add user to group client.AddUserToCurrentGroup(tbUserToAdd.Text); tbUserToAdd.Text = string.Empty; FillUserList(); } catch (Exception ex) { _log.Error(ex.ToString()); } }