[英]How to add a new item to dropdownlist when no records are found in database
如果在mysql數據庫中找不到任何項目,如何向dropdownlist添加替代項目。
這是我嘗試過的
Sub getstudent()
Try
Dim val As String = System.Configuration.ConfigurationManager.ConnectionStrings("val").ConnectionString
Using mycon As New MySqlConnection(val)
Using ds As New DataTable
mycon.Open()
Dim SQL As String = "SELECT reg_no, name FROM tbl_students where class='" & Dpclass.SelectedItem.Text & "' and sub_class='" & Dpsub_class.SelectedItem.Text & "' and acad_session='" & acad_session.SelectedItem.Text & "'"
Dim myCommand As New MySqlCommand(SQL, mycon)
Dim myDA As New MySqlDataAdapter
myDA.SelectCommand = myCommand
myDA.Fill(ds)
mycon.Close()
Dpname.DataSource = ds
Dpname.DataTextField = "name"
Dpname.DataValueField = "reg_no"
Dpname.DataBind()
If Dpname.DataTextField < 1 Then
Dpname.Text = "Nothing Found"
End If
Dpname.Items.Insert(0, New ListItem("-select-", "0"))
End Using
End Using
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
我收到錯誤:從字符串“name”到“Double”類型的轉換無效。
檢查你的DataTable是否為空,用另一個值填充它:
If ds.Rows.Count = 0 Then
Dpname.DataSource = new DataTable()
End If
我不能確定這是答案,因為我不知道你正在使用的表的結構,但從我看到的和給出的錯誤看起來你正在添加0作為字符串,它期待一個雙。 嘗試以下方法:
Dpname.Items.Insert(0, New ListItem("-select-", 0))
我終於明白了,感謝Mahdy Aslamy
If ds.rows.count = 0 then
Dpname.items.insert(0, New ListItem("No records Found", "0"))
Else
Dpname.items.insert(0, New ListItem("-Select-, "0""))
End If
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