小编use*_*785的帖子

即时通讯从数据库中获取价值。出现错误，提示“从DBNULL转换为Double无效。” 有人，请帮助我吗？

公共函数Total（）为Double Dim Total为Double

    Dim strConn As String
    strConn = ConfigurationManager.ConnectionStrings("***").ToString
    Dim conn As New SqlConnection(strConn)

    Dim strSql As String
    strSql = "SELECT SUM (p.Price * c.Quantity) as 'Total' " & _
    "FROM CartItem sci INNER JOIN Product p ON c.ProductID=p.ProductID " & _
    "WHERE c.CartID=@CartID "

    Dim cmd As New SqlCommand(strSql, conn)

    cmd.Parameters.AddWithValue("@CartID", CartID)

    Dim da As New SqlDataAdapter(cmd)

    Dim ds As New DataSet

    conn.Open()

    da.Fill(ds, "CartItem")

    conn.Close()

    If (ds.Tables("CartItem").Rows.Count) <> 0 Then
        **Total = ds.Tables("ShopCartItem").Rows(0)("Total")**
    Else
        Total …