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BOOK: Beginning ASP.NET 3.5 : in C# and VB BOOK ISBN: 978-0-470-18759-3
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Old May 2nd, 2008, 08:24 PM
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Default Two Level Dynamic DropDown List Error Question

I am trying to dynamicly load selections in a DropDown List based on the section that was selected in the first drop down and display a message when the button is clicked. I get an error message concerning the void on the button click. I will include all of the code for your review.

Thank you,


Mark up code
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="TwoLevelDropDown.aspx.cs" Inherits="Demos_TwoLevelDropDown" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>

    <form id="form1" runat="server">
    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True"
        onselectedindexchanged="DropDownList1_SelectedInde xChanged">

    <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="false">

    <asp:Button ID="Button1" runat="server" Font-Bold="True"
        onclick="Button1_Click" Text="Selections Button" />


C# Code

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

public partial class Demos_TwoLevelDropDown : System.Web.UI.Page
    protected void Page_Load(object sender, EventArgs e)


    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        string[] CarArray = new string[4] { "Ford", "Honda", "BMW", "Dodge" };
        string[] AirplaneArray = new string[3] { "Boeing 777", "Boeing 747", "Boeing 777" };
        string[] TrainArray = new string[3] { "Bullet Train", "Amtrack", "Tram" };

        if (DropDownList1.SelectedValue == "Car")
            DropDownList2.DataSource = CarArray;
        else if(DropDownList1.SelectedValue == "Airplane")
            DropDownList2.DataSource = AirplaneArray;
            DropDownList2.DataSource = TrainArray;

protected void Button1_Click(object sender, EventArgs e)
  Response.Write("You selected <b>" +
        DropDownList1.SelectedValue.ToStrng() + ": " +
        DropDownList2.SelectedValue.ToString() + "</b>");
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Old May 3rd, 2008, 02:37 AM
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Hi there,

Is this related to the book Beginning ASP.NET 3.5? If so, can you specify which chapter / page this is about?

If it's not related, can you please post this question in the general Beginning ASP.NET forum: http://p2p.wrox.com/forum.asp?FORUM_ID=348


Imar Spaanjaars
Everyone is unique, except for me.
Author of Beginning ASP.NET 3.5 : in C# and VB, ASP.NET 2.0 Instant Results and Dreamweaver MX 2004
Want to be my colleague? Then check out this post.

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