Binding DropDownList Dynamically

knight1907 · April 3rd, 2006, 12:25 PM

Hi there.
It's a simple procedure hovewer i couldnt accomplish it.
I would like to fill a drop down list dynamically from a data table. The metter is that, i want to do that in code-behind part.

Actually I'm filling the drop down list and binding it, hovewer it seems empty at web page.

I know a solution like adding every row's values of data table to drop down list with Item.Add method in a loop, but i didn't like it. Is there any alternative way ? (C#)
(Also i did it with reader too, but looking for solution related with datatabel)

Thanks for any consideration................

jbenson001 · April 3rd, 2006, 02:35 PM

if you want to bind to a datatabble then you have to do it in the codebehind
otherwiese you will have to add listitems in a loop as you say.

I don't know why you are opposed to either method, but those are your choices unless you hard code the values.

knight1907 · April 3rd, 2006, 03:58 PM

In fact, the situation is a bit complicated, at least for me.

I have a GridView and it takes its data from two tables. In the two of it's EditItemTeplates, I put DropDownLists. Second DDL data changes related to first DDL's selected item.

When the EditCommand(for GridView) event fired, both of them are filled properly, but when i change first DDL's selcted value VS gives an error that is 'there is no data' or something like that for second DDL.

Instead of using DropDownList taken from ToolBox and adding a datasource, I have tried to create a DropDownList in codebehinde part with datatable bounded out of gridview.

I made a search on Internet for such case, i didnt find a good example.

Do you have any suggesion for that situation ?

jbenson001 · April 3rd, 2006, 10:07 PM

What is the exact error? Is it object not set to an instance of an object?

What is the code you have so far? It's a little complicated to do what you want, but not impossible. I have done it before.

Get the exact error and show the code behind you have so far.

knight1907 · April 4th, 2006, 02:58 AM

Code:

 <EditItemTemplate>
   <asp:DropDownList ID="editMarkaDdl" runat="server" DataSourceID="editMarkaDs" 
     DataTextField="marka" DataValueField="markaId" SelectedValue='<%# Bind("markaId") %>' AutoPostBack="true"  OnSelectedIndexChanged="editMarkaDdl_SelectedIndexChanged">
  </asp:DropDownList>

<asp:AccessDataSource ID="editMarkaDs" runat="server" DataFile="~/App_Data/vehiclesDb.mdb"
SelectCommand="SELECT [marka], [markaId] FROM [markaTbl] WHERE ([vehicleTypeId] = ?)">
<SelectParameters>
  <asp:ControlParameter ControlID="vehicleTypeDdl" Name="vehicleTypeId"   PropertyName="SelectedValue" Type="Int32" />

/*vehicleTypeDdl is another DDL on the page (out of the gridview), there is no trouble whit it */

</SelectParameters>
</asp:AccessDataSource>
</EditItemTemplate>

<ItemTemplate> 
<asp:Label ID="Label1" runat="server" Text='<%# Eval("marka") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
                           
<asp:TemplateField HeaderText="MODEL" SortExpression="model">
   <EditItemTemplate>
<asp:DropDownList ID="editModelDdl" runat="server" DataSourceID="editModelDs" DataTextField="model" DataValueField="model" SelectedValue='<%#Bind("model") %>'>
</asp:DropDownList>

<asp:AccessDataSource ID="editModelDs" runat="server" DataFile="~/App_Data/vehiclesDb.mdb"
SelectCommand="SELECT DISTINCT [model] FROM [modelTbl] WHERE ([markaId] = ?)">
<SelectParameters>
 <asp:ControlParameter ControlID="editMarkaDdl" Name="markaId" PropertyName="SelectedValue" Type="Int32" />
</SelectParameters>
</asp:AccessDataSource>
</EditItemTemplate>

Here is the ASP code.
When I hit edit button of girdview, editMarkaDdl and editModelDdl fill properly. When I change the selected value of editMArkaDdl, it says "There is no source code available at the current location".

After opening the Disassembly there another error InvalidOperationException --> Databinding methods such as Eval(), XPath(), and Bind() can only be used in the context of a databound control.

I know I must take care of editMarkaDdl_SelectedIndexChanged but I don't know how.

I mean, at the beginnig of editcommand of gridview, it binds two DDL's properly, then it fails.

By the way, jbenson thanks for consideration......

jbenson001 · April 4th, 2006, 09:01 AM

The problem is that editMarkaDd1 is in a template column. You must have added the control parameter manually because it won't see a template item. You have to use the row databound event to get a reference to the ddl. Something like:

    Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles GridView1.RowDataBound
        If e.Row.RowType = DataControlRowType.DataRow Then
            Dim ddl As New DropDownList
            ddl = e.Row.Cells(cell index).FindControl("editMarkaDdl")

        End If
    End Sub