Weird happenings with DropDownLists and DataTables

heversin · Apr 28, 2012

Hi, How is it possible for two DropDownLists to be databound to identical DataTables yet display them differently? I used VB.NET to create a DataTable (containing a list of names) from an Access DB, and display this DataTable via a DropDownList. Then I inserted a new row at position 0 into the DataTable, so that the initially displayed value would be "SELECT A NAME". So far, so good. Then, having learning something about creating custom objects, I created my own "Database" object, with two methods, one to create DataTables, and another to insert rows into those DataTables at the specified position. I used this custom object to pull the data out of Access, put it in a DataTable, insert a new row at position 0, and display the DataTable via a DropDownList. Now, the problem. The trouble is, when I did everything using my custom object, although EXACTLY THE SAME DataTable is created as first time round, it does NOT display the same way! The added row "SELECT A NAME" is displayed at the BOTTOM of the DropDownList, instead of being the first item (which is what I want). I can't understand why this is happening. I even went to the trouble of iterating through both DataTables (one created with the custom object, one normally) and displaying the contents on the screen so I could visually check that the content of both DataTables is identical. Can anyone tell me what's going on here? Maybe it's something really simple.... Thanks, JON __________________________________________________ _____________________________ +++++++++++++++++++++ MainPage.aspx +++++++++++++++++++++ <%@ Page Language="VB" Debug="true" Trace="false" %> <%@ Import Namespace="System.Data" %> <%@ Import Namespace="System.Data.OleDb" %> <script runat="server"> sub Page_Load(obj as object, e as eventargs) '*** Set variables for my custom object (code in file Database.vb) dim objDatabase as new BusinessObjects.Database objDatabase.ConnectionString = ConfigurationSettings.AppSettings("ConnectionString") Dim ds as new DataSet() objDataBase.DataSet = ds '*** Create DataTable via custom object method DDL1.DataSource = objDatabase.CreateDataTableDefaultView("ExampleDataTable", "SELECT tblPeople.PersonID, tblPeople.LastName FROM tblPeople;") '*** insert row at position 0 into DataTable via custom object method objDatabase.InsertIntoDataTable("ExampleDataTable", 0, "PersonID", -1, "LastName", "SELECT A NAME") '*** Bind DDL1 to this DataTable DDL1.DataTextField = "LastName" DDL1.DataValueField = "PersonID" DDL1.DataBind() '*** Create a DataTable via normal VB.NET (no custom object) Dim objConn as New OleDbConnection ( ConfigurationSettings.AppSettings("ConnectionString") ) Dim objAdapter as New OleDbDataAdapter ( "SELECT tblPeople.PersonID, tblPeople.LastName FROM tblPeople;", objConn ) objAdapter.Fill(ds, "ExampleDataTable2") '*** insert row at position 0 into DataTable via normal VB.NET Dim DefaultItemParentDataRow as DataRow = ds.Tables("ExampleDataTable2").NewRow() DefaultItemParentDataRow("PersonID") = -1 DefaultItemParentDataRow("LastName") = "SELECT A NAME" ds.Tables("ExampleDataTable2").Rows.InsertAt(DefaultItemParentDataRow, 0) '*** Bind DDL2 to this second DataTable DDL2.DataSource = ds.Tables("ExampleDataTable2") DDL2.DataTextField = "LastName" DDL2.DataValueField = "PersonID" DDL2.DataBind() '*** Iterate through and display content of both DataTables to prove they are identical Dim myRow as DataRow For each myRow in ds.Tables("ExampleDataTable").Rows Response.Write("Person ID: " & myRow.Item("PersonID") & " and LastName is " & myRow.Item("LastName") & " ") next myRow Response.Write("<hr>") For each myRow in ds.Tables("ExampleDataTable2").Rows Response.Write("Person ID: " & myRow.Item("PersonID") & " and LastName is " & myRow.Item("LastName") & " ") next myRow end sub </script> <html><body> <form runat="server"> DDL1 - populated via custom object objDatabase ("SELECT A NAME" displays at END of DDL): <asp

ropDownList runat="server" id="DDL1" /> <hr> DDL2 - populated via normal vb.net code ("SELECT A NAME" displays at BEGINNING of DDL): <asp

ropDownList runat="server" id="DDL2" /> </form> </body></html> +++++++++++++++++++++++++++++++++ Database.vb +++++++++++++++++++++++++++++++++ Imports System Imports System.Data Imports System.Data.OleDb Imports System.Collections Namespace BusinessObjects Public Class Database public ConnectionString as String public DataSet as DataSet private objConn as OleDbConnection private objCmd as OleDbCommand private objAdapter as OleDbDataAdapter public function CreateDataTableDefaultView(DataTableName as String, strQuery as string) as DataView try objConn = new OleDbConnection(ConnectionString) objAdapter = New OleDbDataAdapter(strQuery, objConn) objAdapter.Fill(DataSet, DataTableName) return DataSet.Tables(DataTableName).DefaultView catch ex as OleDbException return nothing end try end function public function InsertIntoDataTable(DataTableName as String, insertAt as Integer, FirstColumnName as String, FirstColumnValue as Integer, SecondColumnName as String, SecondColumnValue as String) Dim myDataRow as DataRow = DataSet.Tables(DataTableName).NewRow() myDataRow(FirstColumnName) = FirstColumnValue myDataRow(SecondColumnName) = SecondColumnValue DataSet.Tables(DataTableName).Rows.InsertAt(myData Row, insertAt) End function End Class End Namespace

Weird happenings with DropDownLists and DataTables

heversin

New Member