Re: DropDownList SelectedIndex problem in C# (from working VB.NET)

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From: Rishad Quazi (rishadq_at_yahoo.com)
Date: 04/29/04 

Date: 29 Apr 2004 15:42:07 -0700

Hi Folks,

Ok, after an afternoon of scouring the net, and generally coming up
empty, I reverted to my strategy of trial-and-error. And lo and
behold, I hit upon it! (and subsequently did the coder's victory dance
around my office :)

Alright, here is the solution to the lengthy problem described below:

The piece of code that invokes the SelectedIndex handler in VB.NET
appears as:

<asp:DropDownList id="ddlPublisher" runat="server"
 DataTextField="pub_name"
 DataValueField="pub_id"
 DataSource="<%# GetPublishers() %>"
 SelectedIndex='<%# GetSelectedIndex(Container.DataItem("pub_id")) %>'
 />

.... and the corresponding C# version is (drum roll):

<asp:DropDownList
        id="ddlPublisher"
        runat="server"
        DataTextField="pub_name"
        DataValueField="pub_id"
        DataSource="<%# GetPublishers() %>"
SelectedIndex='<%# GetSelectedIndex(DataBinder.Eval(Container.DataItem,
"pub_id").ToString()) %>' >

The last line makes all the difference. I have a feeling that it could
be shortened or expressed more succintly, but it works, and I can go
home happy tonight!

Thanks everyone,

     - RQ

rishadq@yahoo.com (Rishad Quazi) wrote in message news:<6e4bd275.0404290959.63189dd0@posting.google.com>...
> Hello All,
>
> I've been diligently going through the examples in Scott Mitchell's
> "ASP Data Web Controls" book (I would recommend this work -- cleared
> up a lot of questions for me). All of the examples are in VB.NET and
> though I've been able to convert pretty much all of the examples so
> far into C# (my preferred language), there's one critical example that
> has me stumped. In Chapter 9, he demonstrates how to create a DataGrid
> containing a column with a DropDownList containing a foreign key to
> another table (using the pubs database, displaying the books table
> with FK to publishers name table).
>
> Here's the working VB.NET example:
>
> http://2602a.frsc01.forestry.ubc.ca/KickStartVB/Listing9.7.aspx
>
> I managed to get the VB.NET example to work perfectly, but am stumped
> at a critical step of converting it to C#.
>
> Here's the code for the VB.NET example:
>
> .
> .
> .
> .
>
>
> <asp:DataGrid runat="server" id="dgTitle" Font-Name="Verdana"
> Font-Size="9pt"
>
> CellPadding="5"
> AlternatingItemStyle-BackColor="#dddddd" AutoGenerateColumns="False"
>
> DataKeyField="title_id"
> OnEditCommand="dgTitle_EditRow" OnUpdateCommand="dgTitle_UpdateRow"
>
> OnCancelCommand="dgTitle_CancelRow">
> <HeaderStyle BackColor="Navy" ForeColor="White" Font-Size="13pt"
> Font-Bold="True"
>
> HorizontalAlign="Center" />
> <Columns>
> <asp:EditCommandColumn ButtonType="LinkButton" HeaderText="Edit"
>
> EditText="Edit" UpdateText="Update" CancelText="Cancel" />
> <asp:BoundColumn DataField="title" HeaderText="Title" ReadOnly="True"
> />
> <asp:TemplateColumn HeaderText="Publisher">
> <ItemTemplate>
> <%# DataBinder.Eval(Container.DataItem, "pub_name") %>
> </ItemTemplate>
> <EditItemTemplate>
> <asp:DropDownList id="ddlPublisher" runat="server"
> DataTextField="pub_name"
> DataValueField="pub_id"
> DataSource="<%# GetPublishers() %>"
> SelectedIndex='<%# GetSelectedIndex(Container.DataItem("pub_id")) %>'
> />
> </EditItemTemplate>
> </asp:TemplateColumn>
> <asp:BoundColumn DataField="price" DataFormatString="{0:c}"
>
> HeaderText="Price" ReadOnly="True" />
> </Columns>
> </asp:DataGrid>
>
>
> And the server-side code:
>
> Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles
>
> MyBase.Load
> 'Put user code to initialize the page here
> If Not Page.IsPostBack Then
> BindData()
> End If
>
> End Sub
>
> Dim ddlDataSet As DataSet = New DataSet
>
> Sub BindData()
> '1. Create a connection
> Const strConnString As String =
> "server=XXX;uid=pubs;pwd=XXX;database=pubs"
> Dim objConn As New SqlConnection(strConnString)
>
> '2. Create a command object for the query
> Dim strSQL As String = _
> "SELECT title_id, title, t.pub_id, p.pub_name, price FROM titles t " &
> _
> "INNER JOIN publishers p ON t.pub_id = p.pub_id ORDER BY title"
> Dim objCmd As New SqlCommand(strSQL, objConn)
>
> objConn.Open() 'Open the connection
>
> 'Finally, specify the DataSource and call DataBind()
> dgTitle.DataSource =
> objCmd.ExecuteReader(CommandBehavior.CloseConnection)
> dgTitle.DataBind()
>
> objConn.Close() 'Close the connection
> End Sub
>
>
> Function GetPublishers() As DataSet
> '1. Create a connection
> Const strConnString As String =
> "server=XXX;uid=pubs;pwd=XXX;database=pubs"
> Dim objConn As New SqlConnection(strConnString)
>
> '2. Create a command object for the query
> Const strSQL As String = _
> "SELECT pub_id, pub_name FROM publishers ORDER BY pub_name"
>
> Dim myDataAdapter As SqlDataAdapter
> myDataAdapter = New SqlDataAdapter(strSQL, objConn)
>
> 'Fill the DataSet
> objConn.Open() 'Open the connection
> myDataAdapter.Fill(ddlDataSet, "Publishers")
> objConn.Close() 'Close the connection
>
> Return ddlDataSet 'Return the DataSet
> End Function
>
>
> Function GetSelectedIndex(ByVal pub_id As String) As Integer
> 'Loop through the DataSet ddlDataSet
> Dim iLoop As Integer
> Dim dt As DataTable = ddlDataSet.Tables("Publishers")
> For iLoop = 0 To dt.Rows.Count - 1
> If pub_id = dt.Rows(iLoop)("pub_id").ToString() Then
> Return iLoop
> End If
> Next iLoop
> End Function
>
>
> Sub dgTitle_EditRow(ByVal sender As Object, ByVal e As
> DataGridCommandEventArgs)
> dgTitle.EditItemIndex = e.Item.ItemIndex
> BindData()
> End Sub
>
> Sub dgTitle_UpdateRow(ByVal sender As Object, ByVal e As
> DataGridCommandEventArgs)
> 'Get information from columns...
> Dim ddlPublishers As DropDownList =
> e.Item.Cells(2).FindControl("ddlPublisher")
>
> Dim titleID As String = dgTitle.DataKeys(e.Item.ItemIndex)
>
>
> 'Update the database...
> Dim strSQL As String
> strSQL = "UPDATE titles SET pub_id = @pubIDParam " & _
> "WHERE title_id = @titleIDParam"
>
> Const strConnString As String =
> "server=XXX;uid=pubs;pwd=XXX;database=pubs"
> Dim objConn As New SqlConnection(strConnString)
>
> Dim objCmd As New SqlCommand(strSQL, objConn)
>
> Dim pubIDParam As New SqlParameter("@pubIDParam", SqlDbType.Char, 4)
> Dim titleIDParam As New SqlParameter("@titleIDParam",
> SqlDbType.VarChar, 6)
>
> pubIDParam.Value = ddlPublishers.SelectedItem.Value
> objCmd.Parameters.Add(pubIDParam)
>
> titleIDParam.Value = titleID
> objCmd.Parameters.Add(titleIDParam)
>
> 'Issue the SQL command
> objConn.Open()
> objCmd.ExecuteNonQuery()
> objConn.Close()
>
> dgTitle.EditItemIndex = -1
> BindData()
> End Sub
>
> Sub dgTitle_CancelRow(ByVal sender As Object, ByVal e As
> DataGridCommandEventArgs)
> dgTitle.EditItemIndex = -1
> BindData()
> End Sub
>
>
>
> .
> .
> .
> .
> .
> and here is my non-working C# version. The part that does not work is
> the SelectionIndex section of the front-end code - if I omit it, the
> page works fine, except that when I go into edit mode for a row, the
> dropdown list defaults to the first entry in the list, as expected.
>
> .
> .
> .
> .
>
>
> <asp:DataGrid runat="server" id="dgTitle" Font-Name="Verdana"
>
> Font-Size="9pt" CellPadding="5"
> AlternatingItemStyle-BackColor="#dddddd"
>
> AutoGenerateColumns="False" DataKeyField="title_id"
> OnEditCommand="dgTitle_EditRow" OnUpdateCommand="dgTitle_UpdateRow"
>
> OnCancelCommand="dgTitle_CancelRow"
> Font-Names="Verdana">
> <AlternatingItemStyle BackColor="#DDDDDD"></AlternatingItemStyle>
> <HeaderStyle Font-Size="13pt" Font-Bold="True"
>
> HorizontalAlign="Center" ForeColor="White"
> BackColor="Navy"></HeaderStyle>
> <Columns>
> <asp:EditCommandColumn ButtonType="LinkButton"
>
> UpdateText="Update" HeaderText="Edit" CancelText="Cancel"
> EditText="Edit"></asp:EditCommandColumn>
> <asp:BoundColumn DataField="title" ReadOnly="True"
> HeaderText="Title"></asp:BoundColumn>
> <asp:TemplateColumn HeaderText="Publisher"> <ItemTemplate>
> <%# DataBinder.Eval(Container.DataItem, "pub_name") %>
> </ItemTemplate>
> <EditItemTemplate>
> <asp:DropDownList id="ddlPublisher"
> runat="server" DataTextField="pub_name" DataValueField="pub_id"
> DataSource="<%# GetPublishers() %>"
>
> *** PROBLEM CODE IS HERE ***
> SelectedIndex='< % # GetSelectedIndex(Container.DataItem("pub_id")) %
> >'
> *** PROBLEM CODE ENDS HERE ***
> />
> </EditItemTemplate>
> </asp:TemplateColumn>
> <asp:BoundColumn DataField="price" ReadOnly="True" HeaderText="Price"
> DataFormatString="{0:c}"></asp:BoundColumn>
> </Columns>
> </asp:DataGrid>
>
>
> Server side code:
>
> .
> .
> .
>
> public class ForeignKeyDDL : System.Web.UI.Page
> {
> protected System.Web.UI.WebControls.DataGrid dgTitle;
> protected DataSet ddlDataSet = new DataSet();
>
> private void Page_Load(object sender, System.EventArgs e)
> {
>
> if (!IsPostBack)
> BindData();
>
> }
>
>
> private void BindData() {
>
> // create conn string
> string strConn = "server=XXX;uid=pubs;pwd=XXX";
>
> SqlConnection conn = new SqlConnection(strConn);
>
> // create command obj for the query
> string strSQL = "SELECT title_id, title, t.pub_id, p.pub_name, price
> FROM
>
> titles t ";
> strSQL += "INNER JOIN publishers p ON t.pub_id = p.pub_id
>
> ORDER BY title";
>
> SqlCommand cmd = new SqlCommand(strSQL, conn);
>
> conn.Open();
>
> dgTitle.DataSource =
> cmd.ExecuteReader(CommandBehavior.CloseConnection);
> dgTitle.DataBind();
>
> conn.Close();
>
> }
>
> protected DataSet GetPublishers() {
>
> // create conn string
> string strConn = "server=XXX;uid=pubs;pwd=XXX";
>
> SqlConnection conn = new SqlConnection(strConn);
>
> // create command obj for the query
> string strSQL = "SELECT pub_id, pub_name from publishers order by
>
> pub_name";
>
> SqlDataAdapter da = new SqlDataAdapter();
>
> da = new SqlDataAdapter(strSQL, conn);
>
> conn.Open();
> da.Fill(ddlDataSet, "Publishers");
> conn.Close();
>
> return ddlDataSet;
>
> }
>
> protected int GetSelectedIndex(string pub_id) {
>
> int iLoop;
> DataTable dt = ddlDataSet.Tables["Publishers"];
>
> for (iLoop=0; iLoop<dt.Rows.Count - 1; iLoop++) {
>
> if (pub_id.Equals(dt.Rows[iLoop]["pub_id"].ToString()))
> return iLoop;
> };
>
> return 0;
>
> }
>
> protected void dgTitle_EditRow(object sender, DataGridCommandEventArgs
> e) {
>
> dgTitle.EditItemIndex = e.Item.ItemIndex;
> BindData();
>
> }
>
> protected void dgTitle_UpdateRow(object sender,
> DataGridCommandEventArgs e) {
>
> // get information from columns
> DropDownList ddlPublishers = (DropDownList)
>
> e.Item.Cells[2].FindControl("ddlPublisher");
>
> string titleID = dgTitle.DataKeys[e.Item.ItemIndex].ToString();
>
> // update the database
> string strSQL = "UPDATE titles set pub_id= @pubIDParam where
>
> title_id=@titleIDParam";
>
> string strConn = "server=XXX;uid=pubs;pwd=XXX;database=pubs;";
>
> SqlConnection conn = new SqlConnection(strConn);
>
> SqlCommand cmd = new SqlCommand(strSQL, conn);
>
> SqlParameter pubIDParam = new SqlParameter("@pubIDParam",
> SqlDbType.Char,
>
> 4);
> SqlParameter titleIDParam = new SqlParameter("@titleIDParam",
>
> SqlDbType.VarChar, 6);
>
> pubIDParam.Value = ddlPublishers.SelectedItem.Value;
> cmd.Parameters.Add(pubIDParam);
>
> titleIDParam.Value = titleID;
> cmd.Parameters.Add(titleIDParam);
>
> // issue the SQL command
> conn.Open();
> cmd.ExecuteNonQuery();
> conn.Close();
>
> dgTitle.EditItemIndex = -1;
> BindData();
>
> }
>
> protected void dgTitle_CancelRow(object sender,
> DataGridCommandEventArgs e) {
>
> dgTitle.EditItemIndex = -1;
> BindData();
>
> }
>
>
> .
> .
> .
>
>
>
> I think the C# server side code is working fine. My problem is with
> the syntax in the front-end .aspx code. When I try to run the code, I
> get the following compile time error:
>
> .
> .
> .
>
> Description: An error occurred during the compilation of a resource
> required to service this
> request. Please review the following specific error details and modify
> your source code appropriately.
>
> Compiler Error Message: CS0118:
> 'System.Web.UI.WebControls.DataGridItem.DataItem' denotes a
>
> 'property' where a 'method' was expected
>
> Source Error:
>
>
>
> Line 26: </ItemTemplate>
> Line 27: <EditItemTemplate>
> Line 28: <asp:DropDownList id="ddlPublisher"
>
> runat="server" DataTextField="pub_name" DataValueField="pub_id"
> DataSource="<%# GetPublishers() %>"
> Line 29: SelectedIndex='<%#
> GetSelectedIndex(Container.DataItem("pub_id")) %>'
>
> />
> Line 30: </EditItemTemplate>
>
> .
> .
> .
>
> I've pretty sure the problem is with my expression of the
> SelectedIndex attribute of the
> EditItemTemplate, but I've tried quite a few combinations and nothing
> seems to work.
>
> Sorry about the long post folks.
>
> Thanks again for any help anyone can provide.
>
> Regards,
>
> - Rishad

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