CODEWITHSUNDEEP
c#asp.net
tesla
tesla

Reputation: 21

MSDN DropDownList example does always return the first value

I really need some help because I can't figure it out myself. Despite I have followed many tutorial my dropdownlist is always returning the first value. So today I've decided to use a code that it should work since it's from msdn.microsoft web site.

I've tried into my index.aspx both c# codes but neither works, it's always return to 'white' (first value). Can anyone please enlighten me.

(ps: I've to use .NET 3.5 mvc2 and I'm using vs 2008)

Thanks.

edit: my index.aspx

edit2: Well, the inexperience made ​​me assume the wrong notion, I was working onto mvc.ViewPage instead of UI.Page. Now it's all working. Thanks again.

<%@ Page Language="C#" AutoEventWireup="True" %>
<%@ Import Namespace="System.Data" %>

<!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" >
<script runat="server" >

  void Selection_Change(Object sender, EventArgs e)
  {
     // 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.SelectedItem.Value);

  }

  void Page_Load(Object sender, EventArgs e)
  {

     // Load data for the DropDownList control only once, when the  
     // page is first loaded. 
     if(!IsPostBack)
     {
        // Specify the data source and field names for the Text  
        // and Value properties of the items (ListItem objects)  
        // in the DropDownList control.
        ColorList.DataSource = CreateDataSource();
        ColorList.DataTextField = "ColorTextField";
        ColorList.DataValueField = "ColorValueField";

        // Bind the data to the control.
        ColorList.DataBind();

        // Set the default selected item, if desired.
        ColorList.SelectedIndex = 0;

     }

  }

  ICollection CreateDataSource() 
  {
     // Create a table to store data for the DropDownList control.
     DataTable dt = new DataTable();

     // Define the columns of the table.
     dt.Columns.Add(new DataColumn("ColorTextField", typeof(String)));
     dt.Columns.Add(new DataColumn("ColorValueField", typeof(String)));

     // Populate the table with sample values.
     dt.Rows.Add(CreateRow("White", "White", dt));
     dt.Rows.Add(CreateRow("Silver", "Silver", dt));
     dt.Rows.Add(CreateRow("Dark Gray", "DarkGray", dt));
     dt.Rows.Add(CreateRow("Khaki", "Khaki", dt));
     dt.Rows.Add(CreateRow("Dark Khaki", "DarkKhaki", dt));

     // Create a DataView from the DataTable to act as the data source 
     // for the DropDownList control.
     DataView dv = new DataView(dt);
     return dv;

  }

  DataRow CreateRow(String Text, String Value, DataTable dt)
  {
     // Create a DataRow using the DataTable defined in the  
     // CreateDataSource method.
     DataRow dr = dt.NewRow();

     // This DataRow contains the ColorTextField and ColorValueField  
     // fields, as defined in the CreateDataSource method. Set the  
     // fields with the appropriate value. Remember that column 0  
     // is defined as ColorTextField, and column 1 is defined as  
     // ColorValueField.
     dr[0] = Text;
     dr[1] = Value;

     return dr;

  }
</script>
<head runat="server">
    <title> DropDownList Data Binding Example </title>
</head>
<body>
    <form id="form1" runat="server">
        <h3> DropDownList Data Binding Example </h3>
        Select a background color for days in the calendar.
        <br /><br /> 
        <asp:Calendar id="Calendar1"
        ShowGridLines="True" 
        ShowTitle="True"
        runat="server"/>
        <br /><br /> 
        <table cellpadding="5">
          <tr>
            <td>
                Background color:
            </td>
          </tr>
          <tr>
            <td>
                <asp:DropDownList id="ColorList"
                    AutoPostBack="True"
                    OnSelectedIndexChanged="Selection_Change"
                    runat="server"/>
            </td>
         </tr>
       </table>
    </form>
</body>
</html>

Upvotes: 0

Views: 1355

Answers (1)

guymid
guymid

Reputation: 1206

The most common error with populating a DropDownList is that the DropDownList is bound to data in the page load. Please make sure that the call to populate it is inside a condition for If (!IsPostback)

This will allow it to load the first time but not on postback when you want it to retain the selected choice. If you don't prevent the binding on postback the data is repopulated in the select element and the selected value is lost.

Upvotes: 3

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