“/EMIS”应用程序中的服务器错误。

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行 46：         DS.Clear()
行 47：         DS = GetDataFromDB(sqlstr)
行 48：         If DS.Tables(0).Rows.Count > 0 Then
行 49：             sqlstr = "SELECT*FROM userID WHERE" & "(用户名='" & strID & " ') AND (密码='" & pwd & " ') "
行 50：             Dim myDS As DataSet

[NullReferenceException: 未将对象引用设置到对象的实例。]
   EMIS.WebfrmLogin.Button1_Click(Object sender, EventArgs e) in C:\Inetpub\wwwroot\EMIS\WebfrmLogin.aspx.vb:48
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +108
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +57
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +18
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +33
   System.Web.UI.Page.ProcessRequestMain() +1277




Imports System


Imports System.Data
Imports System.Drawing
Imports System.Data.OleDb

Module ConnToDB
    Public ConnStr As String = "Provider=Microsoft.Jet.OLEDB.4.0;"
    Public ConnectStr As String = ConnStr & "Data Source=E:\寇换龙\data\student.mdb"
    Public DataAdapter As OleDbDataAdapter
    Public DataConnection As OleDbConnection
    Public myDataSet As DataSet
    Public Index As Integer
    Public pepdom As Integer
    Public No As String
    Public Function GetDataFromDB(ByVal sqlstr As String) As DataSet
        Try
            Dim DataConnection As OleDbConnection
            DataConnection.ConnectionString = ConnectStr
            DataAdapter = New OleDbDataAdapter(sqlstr, DataConnection)
            myDataSet = New DataSet
            DataConnection.Open()
            myDataSet.Clear()
            DataAdapter.Fill(myDataSet)
            DataConnection.Close()
            If Not (myDataSet Is Nothing) Then
                Return myDataSet
            End If
        Catch ex As Exception
            Return Nothing
        End Try
    End Function
    

    Public Function UpdateDataBase(ByVal sqlstr As String) As Boolean
        Dim sqlconn As New OleDbConnection(ConnectStr)
        Try
            Dim cmdTable As OleDbCommand = New OleDbCommand(sqlstr, sqlconn)
            cmdTable.CommandType = CommandType.Text
            sqlconn.Open()
            cmdTable.ExecuteNonQuery()
            sqlconn.Close()
        Catch ex As Exception
            Return False
        End Try
        Return True
    End Function
End Module

Public Class WebfrmLogin
    Inherits System.Web.UI.Page
    Public sqlstr As String
    Public strID As String
    Public pwd As String
    Public DS As DataSet
    Public table As String
  
#Region " Web 窗体设计器生成的代码 "

    '该调用是 Web 窗体设计器所必需的。
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

    End Sub
    Protected WithEvents Image1 As System.Web.UI.WebControls.Image
    Protected WithEvents Label1 As System.Web.UI.WebControls.Label
    Protected WithEvents Image2 As System.Web.UI.WebControls.Image
    Protected WithEvents Label2 As System.Web.UI.WebControls.Label
    Protected WithEvents Label3 As System.Web.UI.WebControls.Label
    Protected WithEvents Label4 As System.Web.UI.WebControls.Label
    Protected WithEvents Button1 As System.Web.UI.WebControls.Button
    Protected WithEvents TextBox1 As System.Web.UI.WebControls.TextBox
    Protected WithEvents TextBox2 As System.Web.UI.WebControls.TextBox
    '注意: 以下占位符声明是 Web 窗体设计器所必需的。
    '不要删除或移动它。
    Private designerPlaceholderDeclaration As System.Object

    Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: 此方法调用是 Web 窗体设计器所必需的
        '不要使用代码编辑器修改它。
        InitializeComponent()
    End Sub

#End Region

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        strID = Trim(Me.TextBox1.Text)
        If strID = "" Then
            Me.Label4.Text = "请输入登录的用户名称。"
            Exit Sub
        End If
        pwd = Trim(Me.TextBox2.Text)
        sqlstr = "SELECT*FROM userID WHERE" & "(用户名='" & strID & "') "
        DS = New DataSet
        DS.Clear()
        DS = GetDataFromDB(sqlstr)
        If DS.Tables(0).Rows.Count > 0 Then
            sqlstr = "SELECT*FROM userID WHERE" & "(用户名='" & strID & " ') AND (密码='" & pwd & " ') "
            Dim myDS As DataSet
            myDS = New DataSet
            myDS.Clear()
            myDS = GetDataFromDB(sqlstr)
            If myDS.Tables(0).Rows.Count > 0 Then
                pepdom = myDS.Tables(0).Rows(0)("权限")
                Me.Response.Redirect("http://localhost/EIMS//WebfrmMain.aspx")
            Else
                Me.Label4.Text = "输入的密码不正确，请重新输入密码。"
                Me.TextBox2.Text = ""
            End If
        Else
            Me.Label4.Text = "查无此人，请确认是否有该用户存在。"
            Me.TextBox1.Text = ""
            Me.TextBox2.Text = ""
        End If
    End Sub
End Class