Extend the form to add a label that will display the selected book. Set the autopostback attribute of the drop-down control to true, so that when a selection is made, the page is posted back to the server and the label can be filled with the selected title. <asp:DropDownList autopostback="True" The problem you'll encounter is that when the page is reloaded the data will be reloaded as well, and your selection will be lost. You must protect against that by checking the page's IsPostBack property, which is set to true when the page is posted back, as shown in Example 9-1 (VB.NET) and Example 9-2 (C#).
Example 9-1. Checking IsPostBack in VB.NETPrivate Sub Form_Load(ByVal sender As object, _ ByVal e As System.EventArgs) Handles MyBase.Load If Not IsPostBack( ) Then ' create the array list Dim bookList As New ArrayList( ) ' add all the books bookList.Add("Programming ASP.NET") bookList.Add("Programming C#") bookList.Add("Teach Yourself C++ In 21 Days") bookList.Add("Teach Yourself C++ In 24 Hours") bookList.Add("TY C++ In 10 Minutes") bookList.Add("TY More C++ In 21 Days") bookList.Add("C++ Unleashed") bookList.Add("C++ From Scratch") bookList.Add("XML From Scratch") bookList.Add("Web Classes FS") bookList.Add("Beg. OO Analysis & Design") bookList.Add("Clouds To Code") bookList.Add("CIG Career Computer Programming") ' set the data source ddlBooks.DataSource = bookList ' bind to the data ddlBooks.DataBind( ) Else lblMsg.Text = "Selected book: " & ddlBooks.SelectedItem.Text End If End Sub Example 9-2. Checking IsPostBack in C#private void Page_Load(object sender, System.EventArgs e) { if (! Page.IsPostBack) { // create the array list ArrayList bookList = new ArrayList( ); // add all the books bookList.Add("Programming ASP.NET"); bookList.Add("Programming C#"); bookList.Add("Teach Yourself C++ In 21 Days"); bookList.Add("Teach Yourself C++ In 24 Hours"); bookList.Add("TY C++ In 10 Minutes"); bookList.Add("TY More C++ In 21 Days"); bookList.Add("C++ Unleashed"); bookList.Add("C++ From Scratch"); bookList.Add("XML From Scratch"); bookList.Add("Web Classes FS"); bookList.Add("Beg. OO Analysis & Design"); bookList.Add("Clouds To Code"); bookList.Add("CIG Career Computer Programming"); // set the data source ddlBooks.DataSource=bookList; // bind to the data ddlBooks.DataBind( ); } else { lblMsg.Text = "Selected book: " + ddlBooks.SelectedItem.Text; } } In Example 9-1 and Example 9-2, the IsPostBack property is tested. If it returns true, then the page has been posted back to itself by a user taking an action, and the selected item is displayed. If the IsPostBack property returns false, then the book list is populated with data from the ArrayList. |