Vb.net net数据库查询和复选框，正确的方法怎么办？

我是Vb.net和Sql Server的新手，不要太苛刻。谁能检查一下我的代码，我觉得这样做是不对的。其目的是仅当单击复选框并显示该查询时才显示查询。 多谢各位

 Private Sub btnFilter_Click(sender As Object, e As EventArgs) Handles btnFilter.Click

    CheckValue = 0 'set to value 0 
    'check if any checkbox is checked.
    For Each C As Control In Me.Controls
        If C.GetType Is GetType(CheckBox) Then
            Dim cb As CheckBox = DirectCast(C, CheckBox)
            If cb.Checked Then
                CheckValue = CheckValue + 1 'only works if value is above 1
            End If
        End If
    Next


    If CheckValue <> 0 Then   'only if check box is checked then rest will run

        Try
            If chkboxId.Checked = True Then 'assign value to checkbox
                chkboxIdstr = "userid"
            Else
                chkboxIdstr = ""
            End If

            If chkboxName.Checked = True Then
                chkboxNamestr = "username"
            Else
                chkboxNamestr = ""
            End If

            'to insert comma, only if both are true.
            If chkboxId.Checked = True And chkboxName.Checked = True Then
                SQLcomma = " , "
            Else
                SQLcomma = ""
            End If

            'so if both are checked we get a comma
            SQL2 = chkboxIdstr + " " + SQLcomma + " " + chkboxNamestr
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

        Try 'sql connect and display
            sqlCon.Open()
            SQL = "SELECT " + SQL2 + " FROM user_info"

            Dim dadapter As New SqlDataAdapter(SQL, sqlCon)
            Dim dset As New DataSet
            sqlCon.Close()
            dadapter.Fill(dset)
            'fill datagrid
            dgv.DataSource = dset.Tables(0)

        Catch ex As Exception
            MsgBox(ex.Message)
            sqlCon.Close()
        End Try
    Else
        MsgBox("Plesase do check any box to filter ")
        Exit Sub

    End If
End Sub

-

---

我通过小型应用程序跟踪和出错来学习，主要是通过谷歌搜索解决方案。

我认为您不需要所有这些代码。只需逐个测试您的复选框，并以增量方式构建要添加到SELECT查询中的列列表

Dim selectColumns As String
Try

    If chkboxId.Checked = True Then 
        selectColumns = "userid,"
    End If

    If chkboxName.Checked = True Then
        selectColumns &= "username,"
    End If

    ' Other columns???? follow the same pattern

    ' If we have something in selectColumns then we could execute the query
    ' but before we trim away the last comma
    If selectColumns.Length > 0 Then 
       selectColumns = selectColumn.TrimEnd(",")

       sqlCon.Open()
       SQL = "SELECT " & selectColumns & " FROM user_info"
       .....
    Else
       ' no data in selectColumns? Message for you user
       MsgBox("Plesase do check any box to filter ")
       Exit Sub
    End If    
Catch ex As Exception
    MsgBox(ex.Message)
    sqlCon.Close()
End Try

试试这个：

Private Sub btnFilter_Click(sender As Object, e As EventArgs) Handles btnFilter.Click

    If chkboxId.Checked OrElse chkboxName.Checked Then
        SQL2 = String.Empty
        If chkboxId.Checked Then
            SQL2 = SQL2 + "userid"
        EndIf

        If chkboxId.Checked AndAlso chkboxName.Checked Then
            SQL2 = SQL2 + " , "
        End If

        If chkboxName.Checked Then
            SQL2 = SQL2 + "username"
        End If

        Try 'sql connect and display
            sqlCon.Open()
            SQL = "SELECT " + SQL2 + " FROM user_info"

            Dim dset As New DataSet
            Using dadapter As New SqlDataAdapter(SQL, sqlCon)
                dadapter.Fill(dset)
            End Using

            'fill datagrid
            dgv.DataSource = dset.Tables(0)

          Catch ex As Exception
             MsgBox(ex.Message)
          Finally
             sqlCon.Close()
          End Try
    Else
        MsgBox("Please do check any box to filter ")
    End If

End Sub

---

如果您使用的是SqlDataAdapter，您不需要打开连接，因为它自己就可以完成，这只是一个问题。如果必须向Select语句传递值，您会怎么做？假设您必须选择一行，其中userid为45。你怎么通过45级考试？马努超。我不知道。我会查一查的。好吧，我就为了这个案子告诉你，因为你无法避免：。从user\u info中选择userid，其中userid=@value user\u infodadapter.SelectCommand.Parameters。AddWithValue@value，谢谢你。但我会试试的。谢谢。没有将错误对象引用设置为对象的实例。在为selectColumns赋予价值后，一切正常。史蒂夫，非常感谢你。在业余时间学习编程。