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Why does the dropdownlist always select the same item ?

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chu2654

chu2654

Programmer
Sep 16, 2005
5
TW
Hello, I use a drop downlist "txtmajor" to retrieve data from sql server.

txtmajor.Items.clear()
While reader.Read()
txtmajor.Items.Add(reader.Item("No") & "/" & reader.Item("Subject"))
End While

But when I use txtmajor.SelectedItem.Text.ToString to show the selected item, it is always the first item. How can I solve the problem ?
 
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At what point are you loading the values into the drop down list?

Also, you can simplify your code by binding the reader to the list like so

Code: 
txtmajor.DataSource = reader;
txtmajor.DataValueField = "id";
txtmajor.DataTextField = "Text To Display";
txtmajor.DataBind();

And you can access the selected value with

Code: 
string selectedValue = txtmajor.SelectedValue;
 
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I set the dropdownlist in page_load. Your method still doesn't work.

Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
dim username as string
Call Show_Subject()

End Sub

Sub Show_Subject()
Dim SelectCmd As String
Dim reader As sqlDataReader
SelectCmd = "select no,name from class"
reader = Create_Rd("Diglearning", SelectCmd)
txtmajor.DataSource = reader
txtmajor.DataValueField = "no"
txtmajor.DataTextField = "no"
txtmajor.DataBind()

End Sub

Sub btnSend_Click(ByVal sender As Object, ByVal e As EventArgs)
response.write(txtmajor.SelectedValue)
End Sub

<html>
<head><title></title></head>
<body background="bg1.gif"><center>
<form runat="server">


<asp:DropDownList id="txtmajor" runat="server">
<asp:ListItem>Class</asp:ListItem>
</asp:DropDownList></td>
</tr>





<tr>
<td colspan="2" bgColor=#FFCC66 width="376">
<asp:Button id="btnSend" runat="server" Text="Send" onClick="btnSend_Click"/></td>
</tr>
</table>
<asp:Label id="lblShow1" BackColor="Yellow" runat="server"/>

</asp:panel>
<asp:panel id="panel2" runat="server" width="300" backColor="#CCFFCC">
<asp:Label id="lblShow" runat="server"/>
</asp:panel>
</form></center>
</P>

</body></html>
 
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You are populating the list with each postback

You need to do something like below in the Page_Load. It may not be syntactically perfect, as I am not a VB programmer, but the basic idea is right.

Code: 
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) 
 dim username as string

 if(IsPostBack = false)
  Call Show_Subject()
 End If
    
 End Sub
 
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You also don't need to use the "Call" method in .NET


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Need help finding an answer?

Try the Search Facility or read FAQ222-2244 on how to get better results.

 
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If you want to reload the list every time, use a session variable to capture your selection on the post back. In c# for instance:

if(Page.IsPostBack &&
DropDownList1.SelectedIndex != -1 &&
DropDownList1.SelectedIndex != 0) {
Session["VARIABLE"] = DropDownList1.SelectedValue;
}
DropDownList1.Items.Clear();
//ADD WHATEVER ITEMS YOU WANT TO THE LIST HERE

if(Session["VARIABLE"] != null) {
DropDownList1.SelectedValue = Session["VARIABLE"].ToString().Trim();
} else
DropDownList1.SelectedIndex = 0;

That should work for you if you can translate the concept back to VB....
 
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my 2 pennies, i think its your DataValueField, and DataTextField no populating right...

txtmajor.DataValueField = "no"
txtmajor.DataTextField = "no"

lauch the page with your DDL, then right click the page, view source - scroll to your dropdown list, and it will render as a <SELECT> with <OPTION value="">Bla</OPTION>s

id say post that here, but dont, just make sure each value is unique, the texts can be dup'd though.
 
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