登录验证的问题，帮我看看怎么跳出验证循环，返回主窗口

private void btnLogin_Click(object sender, RoutedEventArgs e)
        {            
            if (String.IsNullOrEmpty(this.cbxLoginName.Text)||String.IsNullOrEmpty(this.txtpwd.Text))
            {
                 MessageBox.Show("用户名、密码不能为空","ERROR",MessageBoxButton.OK,MessageBoxImage.Error);
                return;
            }
            else
            {
                user1 = new BAUser();
                user1.LandName = cbxLoginName.Text;
                user1.Valpwd = txtpwd.Text;               
              
                foreach (var item in users001)
                {
                    if (user1.LandName==item.LandName||user1.Valpwd==item.Valpwd)
                    {
                        this.DialogResult = true;
                        this.Close();
                    }
                   
                }
                    MessageBox.Show("用户名或密码错误，请重新输入", "ERROR", MessageBoxButton.OK, MessageBoxImage.Error);
                    return;
                    this.DialogResult = false; 
            }