vb.net 数据集返回空值

Question

您好，我已经用谷歌搜索了...已经 2 天了...这些空洞的东西真让我头疼! ...请有人告诉我我的代码有什么问题吗？？？？

在这里:-

Public Sub checkemail()
    sqlcheckemail = "select Email from WEBUSER where Email='" + TBEmail.Text + "'"
    Dim dscheckemail As New DataSet
    Dim sqlCnn As New SqlConnection
    'Dim MYNULL As String
    sqlCnn = New SqlConnection(connStr)
    sqlCmd = New SqlCommand(sqlcheckemail, sqlCnn)
    sqlCnn.Open()
    da.SelectCommand = sqlCmd
    da.Fill(dscheckemail)
    'MYNULL = CheckDBNull(dscheckemail)
    'If Not (dscheckemail.Tables.Count > 0) AndAlso (dscheckemail.Tables(0).Rows.Count > 0) Then
    'If Not IsDBNull(dscheckemail) Then
    'If Not (dscheckemail Is Nothing) Then
    'If MYNULL = "NULL" Then
    If Not dscheckemail Is Nothing Then
        LabelGender.Text = "There is something"
        'MsgBox("Unable to register because the E-mail address has already registered as a user, Please register using different Email address or contact administrator")
        'Response.Redirect("~/Rnewuser.aspx")
    Else
        'MsgBox("u can register")
        LabelGender.Text = "NULL"
    End If

    sqlCmd.Dispose()
    sqlCnn.Close()
End Sub

如果你看到我评论过的那个是我已经在谷歌上测试过的那个……所以现在如果电子邮件地址存在于数据库中……一切都很好……但是如果它不存在代码应该处理不满足第一个 if 语句的那个​​……但现在我得到的结果是“有东西”，尽管数据库中不存在电子邮件……

请帮帮我!!!!我以前做过这个无效的事情..但很久以前我没有保存代码..现在我正在为我自己的网站做这件事..这让我很崩溃

Answer 1

dataset 不是nothing 所以进入if，你应该检查里面的datatable。

'is not nothing, but is safer this way
If Not dscheckemail Is Nothing Then

    'Check there is a datatable inside the dataset and that it has rows
    If dscheckemail.Tables(0) Is Nothing OrElse dscheckemail.Tables(0).Rows.Count = 0 Then
        'is really empty
    Else
        'You have a dataTable with data.
    End If

End If