ExecuteReader：连接属性尚未初始化。在 vb.net 2010 中答案

【问题标题】：ExecuteReader: Connection property has not been initialized. in vb.net 2010ExecuteReader：连接属性尚未初始化。在 vb.net 2010 中
【发布时间】：2017-07-21 15:39:49
【问题描述】：

我有一个关于“invalidoperationexception was unhandled”的错误

我的代码是这样的：

 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    sql = "select * from tb_user where user_name='" + TxtUser.Text + "' and user_password='" + txtPass.Text + "'"
    cmd = New SqlCommand(sql, con)
    rd = cmd.ExecuteReader
    If (rd.HasRows) Then
        rd.Read()
        If rd.Item("user_position") = "Manager" Then
            Form5.MasterDataToolStripMenuItem.Visible = False
            Form5.mTransaction.Visible = False
            Form5.mReport.Visible = True
            Form5.mSetting.Visible = False
        ElseIf rd.Item("user_position") = "Admin" Then
            Form5.MasterDataToolStripMenuItem.Visible = True
            Form5.mTransaction.Visible = True
            Form5.mReport.Visible = False
            Form5.mSetting.Visible = True
        ElseIf rd.Item("user_position") = "Operator" Then
            Form5.MasterDataToolStripMenuItem.Visible = False
            Form5.mTransaction.Visible = True
            Form5.mReport.Visible = True
            Form5.mSetting.Visible = False
        End If
        Form5.useractive.Text = rd.Item("user_name")
        Form5.Statusposition.Text = rd.Item("user_position")
        Form5.ShowDialog()
    Else
        MsgBox("Access Denied! Check Username And Password!")
        TxtUser.Clear()
        txtPass.Clear()
        TxtUser.Focus()
    End If
End Sub

错误提示“ExecuteReader：连接属性尚未初始化。” 在这段代码中：

 rd = cmd.ExecuteReader

我不知道我的代码有什么问题。有人可以帮助我吗？我只是这里的新手。谢谢。

【问题讨论】：

推荐阅读msdn.microsoft.com/en-us/library/9kcbe65k(v=vs.110).aspx

标签： vb.net vb.net-2010 executereader

【解决方案1】：

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Using (con = New SqlClient.SqlConnection(yourconnectionString))
    Try
        con.Open();
        Dim sqlQuery As String = "select * from tb_user where user_name='" + TxtUser.Text + "' and user_password='" + txtPass.Text + "'"
        Dim sqlCommand As SqlClient.SqlCommand = New SqlClient.SqlCommand(sqlQuery, con)
        rd = sqlCommand.ExecuteReader()

        If (rd.HasRows) Then
            rd.Read()
            If rd.Item("user_position") = "Manager" Then
                Form5.MasterDataToolStripMenuItem.Visible = False
                Form5.mTransaction.Visible = False
                Form5.mReport.Visible = True
                Form5.mSetting.Visible = False
            ElseIf rd.Item("user_position") = "Admin" Then
                Form5.MasterDataToolStripMenuItem.Visible = True
                Form5.mTransaction.Visible = True
                Form5.mReport.Visible = False
                Form5.mSetting.Visible = True
            ElseIf rd.Item("user_position") = "Operator" Then
                Form5.MasterDataToolStripMenuItem.Visible = False
                Form5.mTransaction.Visible = True
                Form5.mReport.Visible = True
                Form5.mSetting.Visible = False
            End If
            Form5.useractive.Text = rd.Item("user_name")
            Form5.Statusposition.Text = rd.Item("user_position")
            Form5.ShowDialog()
        Else
            MsgBox("Access Denied! Check Username And Password!")
            TxtUser.Clear()
            txtPass.Clear()
            TxtUser.Focus()
        End If

    Catch ex As Exception

    End Try
End Using

结束子

【讨论】：

【解决方案2】：

我怀疑您没有正确设置您在此处使用的“con”变量：

cmd = New SqlCommand(sql, con)

请不要像这样使用字符串连接生成 SQL 查询。使用参数化查询： How do I create a parameterized SQL query? Why Should I?

【讨论】：