DropDownList control

bmains · November 20th, 2003, 11:17 AM

Hello,

I'm using a drop down list control on the page, and I databind it in this manner:

Code:

DropDownList1.DataSource = objDataSet
DropDownList1.DataMember = "DB"
DropDownList1.DataTextField = "name"
DropDownList1.DataValueField = "name"
DropDownList1.DataBind()

The problem I'm having is that of the 40+ records that are loaded into it, when I go to reference it in any of the ways below:

Code:

DropDownList1.SelectedValue
DropDownList1.SelectedItem.Text
DropDownList1.SelectedItem.Value
DropDownList1.SelectedIndex

I only get the first entry. The selected index is zero, and the values and text values is only the first one, no matter what record I have selected. I've tested the SelectedIndexChanged with the AutoPostback to true, and when the index changed, it did post back. But even then, the value was still 0 for the index.

Why is this happening?

Thanks,

Brian Mains

planoie · November 20th, 2003, 11:49 AM

You should handle changes in a dropdownlist using the dropdownlist's eventhandler instead of checking in page load. It's possible you aren't seeing the change, because .Net hasn't checked the control to see if it has changed yet. I would think it would have, but the easy way to solve this is to use the event handler.

For the dropdownlist, you can specify "onSelectedIndexChange" in the control markup and specify the function to call. Inside the function you can then check the SelectedIndex and use SelectedItem and be assured that it will give you the item you actually selected.

From MSDN help:
<code>
      Sub Selection_Change(sender As Object, e As EventArgs)

         ' Set the background color for days in the Calendar control
         ' based on the value selected by the user from the
         ' DropDownList control.
         Calendar1.DayStyle.BackColor = _
             System.Drawing.Color.FromName(ColorList.SelectedIt em.Value)

      End Sub
</code>

<markup>
               <asp:DropDownList id="ColorList"
                    AutoPostBack="True"
                    OnSelectedIndexChanged="Selection_Change"
                    runat="server">

                  <asp:ListItem Selected="True" Value="White"> White </asp:ListItem>
                  <asp:ListItem Value="Silver"> Silver </asp:ListItem>
                  <asp:ListItem Value="DarkGray"> Dark Gray </asp:ListItem>
                  <asp:ListItem Value="Khaki"> Khaki </asp:ListItem>
                  <asp:ListItem Value="DarkKhaki"> Dark Khaki </asp:ListItem>

               </asp:DropDownList>
</markup>

Peter
------------------------------------------------------
Work smarter, not harder.

bmains · November 21st, 2003, 08:52 AM

I do have a OnSelectedIndexChanged event defined for the drop down list. All I had in the page_load event was the data binding information. Any other ideas? Also, where do you specify the data binding information?

Thanks,

Brian

planoie · November 21st, 2003, 10:07 AM

I bind in page load based on Not IsPostback (usually I create a private method to do the binding to the control and call that from page load).

Is your bind conditional based on postback? If not you could have problems, because every time the page loads, you'll end up rebinding the control. When that happens, viewstate and postback data gets all messed up so the framework doesn't raise the correct events. I'll bet that's what's happening.

You only need to bind once (when Not IsPostback). The viewstate will remember what's in the select(and what value was previously selected. That's how it knows which events (OnSelectedIndexChanged) to raise.

Peter
------------------------------------------------------
Work smarter, not harder.

bmains · November 21st, 2003, 01:23 PM

Thanks, that solved the problem. I should have realized that, but I didn't.