Beginning Web Development, Silverlight, and ASP.NET AJAX

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CHAPTER 3 ■ WEB FORMS WITH ASP.NET
Creating Controls at Runtime
Because controls are objects, and because the page controls are a collection, you can also
create controls at runtime. So, if you consider the previous example, you can add a new
list box to the bottom of the form quite easily with this code:
protected void Page_Load(object sender, EventArgs e)
{
foreach(Control ctrl in Page.Controls)
{
ListBox1.Items.Add(ctrl.GetType().ToString() + ":" + ctrl.ID);
}
theHead.Title = "Dynamically Created Title!";
ListBox newListBox = new ListBox();
newListBox.Items.Add(new ListItem("Item on my Dynamic List"));
Page.Form.Controls.Add(newListBox);
}
Note that you have to add a control to a control container—you cannot add it directly
to the page—so Page.Controls.Add will fail. If you want to add it to the top level of the
page, use Page.Form.Controls.Add, as just shown. Additionally, you can add the control to
an existing panel on the page. For example, you can add one to a named panel (Panel1)
like this:
Panel1.Controls.Add(newListBox);
When you run the application, you can see the new list box on your page (see
Figure 3-8).
Of course, you can also handle events on dynamically created controls. You do so by
adding an event handler to the object, specifying the event that you want to handle. So,
for example, if you want to handle a SelectedIndexChanged event on a dynamically created
list, you would do this first by assigning the event handler like this:
newListBox.SelectedIndexChanged +=
new EventHandler(newListBox_SelectedIndexChanged);