读取器关闭时无效尝试调用读取

Question

这是我尝试从登录表单中打开的代码 这是说当阅读器关闭时无效尝试调用读取

    Imports System.Data.SqlClient

    Public Class Form40
    Private Sub Form40_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    Label1.Text = users
    'Dim cmd As New SqlCommand
    Dim user_Name As String
    Dim main_menu1, main_menu2 As String
    If (con.State = ConnectionState.Closed) Then
        Dim cmd As New SqlCommand(" SELECT User_name, main_menu1,main_menu2 FROM users WHERE (User_name = '" & TextBox1.Text & "' )")
        con.Open()
        ' cmd.Connection = con

        ' cmd.CommandText = " SELECT User_name, main_menu1,main_menu2 FROM users WHERE (User_name = '" & TextBox1.Text & "' )"
        Dim ddr As SqlDataReader = cmd.ExecuteReader()
        If ddr.HasRows Then
            While ddr.Read()

                main_menu1 = ddr("main_menu1").ToString()
                main_menu2 = ddr("main_menu2").ToString()
                user_Name = ddr("User_Name").ToString()

                If user_Name = TextBox1.Text And main_menu1 = "True" Then
                    TextBox2.Visible = False
                End If
            End While
        End If
    End If
    con.Close()
End Sub
End Class

这是表单登录的代码

Imports System.Data
Imports System.Data.SqlClient
Public Class LoginForm2
    Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
        ConnectToSQL()
    End Sub
    Private Sub ConnectToSQL()
        Dim Pass_word As String
        Dim Pass_word2 As String
        Dim user_Name As String

        Try
            Dim cmd As New SqlCommand(" SELECT  User_name, Pass_word FROM   users WHERE   (User_name = '" & UsernameTextBox.Text & "' ) AND (Pass_word = '" & PasswordTextBox.Text & "')", con)
            con.Open()
            Dim lrd As SqlDataReader = cmd.ExecuteReader()
            If lrd.HasRows Then
                While lrd.Read()
                    'Do something here
                    Pass_word = lrd("Pass_word").ToString()
                    user_Name = lrd("User_Name").ToString()
                    Pass_word2 = PasswordTextBox.Text()
                    If Pass_word = Pass_word2 And user_Name = UsernameTextBox.Text Then
                        MessageBox.Show("Logged in successfully as " & user_Name, "", MessageBoxButtons.OK, MessageBoxIcon.Information)
                        users = user_Name
                        Me.Hide()
                        Form40.Show()
                        'Clear all fields
                        PasswordTextBox.Text = ""
                        UsernameTextBox.Text = ""
                    End If
                End While
            Else
                MessageBox.Show("Username and Password do not match..", "Authentication Failure", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
                'Clear all fields
                PasswordTextBox.Text = ""
                UsernameTextBox.Text = ""
            End If
            lrd.Close()
        Catch ex As Exception
            MessageBox.Show("Error while connecting to SQL Server." & ex.Message)
        Finally
            con.Close()

        End Try
    End Sub

    Private Sub Cancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Cancel.Click
        Me.Close()
    End Sub
End Class