执行读取器:连接属性尚未初始化. 2010 年 vb.net

Question

我有一个关于"无效操作异常未处理"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

错误显示"执行读取器：连接属性尚未初始化"。 在此代码中：

rd = cmd.ExecuteReader

我不知道我的代码出了什么问题。有人可以帮助我吗？我只是这里的新手。 谢谢。

Answer 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

Answer 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。 使用参数计量查询： 如何创建参数化 SQL 查询？我为什么要这样做？