How are DropDown lists retained on postback?

[Guest]

I have an ASP.NET example which programmatically builds a drop down list.

public class WebForm1 : System.Web.UI.Page
{
protected System.Web.UI.WebControls.DropDownList ddlCategories;

public class WebForm1 : System.Web.UI.Page
{
if (!IsPostBack)
{
// If page is requested for the first time
ddlCategories.Items.Add("Web development");
ddlCategories.Items.Add("Programming Languages");
ddlCategories.Items.Add("Certifications");
}

aString = ddlCategories.SelectedItem.ToString();
}

When it IS a postback, how is the Drop Down list populated?

I have confirmed that the drop down list is not populated in the .aspx file

I have disabled viewstate for the application, the list is still populated,
however the "SelectedItem" property is lost.

TIA

 

[Guest]

Error in the top of the code. It should be...

public class WebForm1 : System.Web.UI.Page
{
protected System.Web.UI.WebControls.DropDownList ddlCategories;

// --- error was here. fixed now. ---
private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
.... etc...

 

[Karch]

The values for the dropdown are already rendered and thus will be part of
the page - take a look at the source in the browser. Therefore, it doesn't
depend on viewstate. However, as you see, the selected item does depend on
viewstate since its a server control. That's why you still have the values
in the dropdown, but none of the control property information (which uses
viewstate). Its really not different than building a static web page (html)
and posting back - the values will still be there because they have already
been rendered.

 

[Guest]

Thanks Karch. That answers it for me.

The values for the dropdown are already rendered and thus will be part of
the page - take a look at the source in the browser. Therefore, it doesn't
depend on viewstate. However, as you see, the selected item does depend on
viewstate since its a server control. That's why you still have the values
in the dropdown, but none of the control property information (which uses
viewstate). Its really not different than building a static web page (html)
and posting back - the values will still be there because they have already
been rendered.