我在应用程序中的登录例程不会将我定向到主窗体

>我正在使用VS2010构建Windows表单应用程序。我想读取用户标识和密码，并使用数据库检查它们的有效性。如果找到合适的匹配项，我想将用户定向到主窗体。当我输入正确的凭据时，我的代码当前没有定向。可能是什么原因？

string connectionstring = "Data Source=localhost;Initial Catalog=HMS;Persist Security Info=True;User ID=Developer;Password=abc@123";
SqlConnection connection = new SqlConnection(connectionstring);
string SelectStatement = "SELECT * FROM Users where UserID = '@UserID' and Password = '@password'";
SqlCommand insertcommand = new SqlCommand(SelectStatement, connection);
insertcommand.Parameters.AddWithValue("@UserID", textBox1.Text);
insertcommand.Parameters.AddWithValue("@password", textBox2.Text);
SqlDataReader reader;
try
{
  connection.Open();
  reader = insertcommand.ExecuteReader();
  while (reader.Read())
  {
    string userid = reader["UserID"].ToString();
    string pass = reader["Password"].ToString();
    if (userid == textBox1.Text.ToString() && pass == textBox2.Text.ToString()) // login successful
    {
      Mainform main = new Mainform();
      this.Hide();
      main.Show();
    }
    else
    {
      MessageBox.Show("Invalid Username or Password!");
    }
  }//end while
  reader.Close();
  }
  catch (Exception ex)
  {
  throw ex;
}//end catch
finally
{
  connection.Close();
}