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ASP.NET: Dynamically set Text and Value fields for a DropDownList
This code was written in response to a message posted on one of the ASPAlliance lists.
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In this article, we will look at a technique that allows us to switch the value and text represenation of the items in a DropDownList. I know, it's
probably not something you will see in many applications but it is yet another example of the power of ASP.NET.
The code sample below uses a few best pratices you should understand and be aware of:
*The code below uses structured error handling techniques in the form of the Try...Catch statement. Go here
to read more about the great new structured error handling we VBers now have.
*The code below also uses a connection string stored in a web.config configuration file. Go here to read more about
the web.config configuration file and how it can be used to store application wide data.
*The code below also follows proper database resouce management per this best practice.
Code:
<%@ Page Language="VB" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<html>
<script language="VB" runat="server">
Sub Page_Load(sender As Object, e As EventArgs)
If Not IsPostBack Then
DropDownList1.DataTextField = "pub_name"
DropDownList1.DataValueField = "pub_id"
BindList()
End If
End Sub
Sub ButtonClick(sender As Object, e As EventArgs)
If sender.ID = "Button1" Then
DropDownList1.DataTextField = "pub_id"
DropDownList1.DataValueField = "pub_name"
Else
DropDownList1.DataTextField = "pub_name"
DropDownList1.DataValueField = "pub_id"
End If
BindList()
Button1.Visible = "False"
Button2.Visible = "True"
End Sub
Sub BindList()
Dim myConnection As SqlConnection = new SqlConnection(ConfigurationSettings.AppSettings("DSN_pubs"))
Dim myCommand As SqlCommand = new SqlCommand("Select pub_id, pub_name From publishers", myConnection)
Dim myDataReader As SqlDataReader
Try
myConnection.Open()
myDataReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection)
DropDownList1.DataSource = myDataReader
DropDownList1.DataBind()
Catch myException As Exception
Response.Write("An error has occurred: " & myException.ToString())
Finally
If Not myDataReader Is Nothing Then
myDataReader.Close()
End If
DropDownList1.Items.Insert(0, "Select an Item")
DropDownList1.SelectedIndex = 0
End Try
End Sub
</script>
<body>
<form runat="Server">
<asp:DropDownList id="DropDownList1" runat="server" />
<asp:Button id="Button1" Text="Switch Em" OnClick="ButtonClick" runat="server" />
<asp:Button id="Button2" Text="Switch Em Back" OnClick="ButtonClick" Visible="False" runat="server" />
</form>
</body>
</html>
Result:
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