If we decide to skip data binding, we are left with two choices of populating a CheckBoxList or a RadioButtonList with their items.

Firstly, we can add items at design time using the ListItemCollection Editor:

Suppose that the above was a screen shot of adding 3 items to a CheckBoxList. At design time, the "aspx" view will show:

  <asp:checkboxlist id=CheckBoxList1
        runat="server">
    <asp:listitem value="Borland">Delphi</asp:listitem>
    <asp:listitem value="Microsoft">VB</asp:listitem>
    <asp:listitem value="MS and Borland">C#</asp:listitem>
  </asp:checkboxlist>

Each item (a single check box) in a CheckBoxList is presented as an ListItem control. The Text property specifies the text displayed in the list control for the item. The Value property allows you to associate a value with the item in the list control, in addition to the text displayed in the control.

At run time, a CheckBoxList will render as a TABLE element if the RepeatLayout is set to RepeatLayout.Table (the default setting). If RepeatLayout.Flow is used, the list is rendered without any table structure (as a SPAN element containing INPUT elements)

Much similar to the CheckBoxList, the RadioButtonList operates on the same prinicples but renders as a set of radio buttons that have their GroupName property "pre-set".

Although we can form the entire list of items using the ListItemCollection Editor (at design time), nothing stops us from dynamically adding or modifying entries at run time as well.

Here's an example, and the steps to build it:

1. Have one design-time CheckBoxList populated as in the above picture
2. Drop a RadioButtonList on a Web Form
3. Add one Label also
4. The "design" should look like:

   

5. Use the Page_Load procedure to populate the RadioButtonList with items. Note that we can check the IsPostback property of the Page in order to fill the list only once. The ViewState will hold and transfer the values between postbacks

   procedure TWebForm5.Page_Load (sender: System.Object; e: System.EventArgs); var idx : integer; sel : string; begin if NOT Page.IsPostBack then //initially begin with RadioButtonList1.Items do begin Add('Show VB'); Add(ListItem.Create('Hide VB')); end; RadioButtonList1.SelectedIndex := 0; RadioButtonList1.AutoPostBack := true; Label1.Text := 'Nothing initially selected'; end else //on every postback ...

   The above code adds two option buttons to the list control and sets some properties. Note the way items are added to the radio button list at run time.

6. Create the event handler for the RadioButtonList's SelectedIndexChanged event, and add the following code:

   procedure TWebForm5. RadioButtonList1_SelectedIndexChanged (sender: System.Object; e: System.EventArgs); var li : ListItem; begin if RadioButtonList1.SelectedIndex = 0 then begin li := ListItem.Create('VB','Microsoft'); CheckBoxList1.Items.Add(li); end else begin li := CheckBoxList1.Items.FindByText('VB'); if li <> nil then CheckBoxList1.Items.Remove(li); end; end;

   Basically, if the "Show VB" option button is clicked, the "VB" item is displayed (re-added if necessary) in the CheckBoxList, otherwise it gets removed from the Items collection.

7. To provide some output, we'll use the Label control. Go back to the Page_Load procedure and add some more code to it:

   ... else //on every postback begin with CheckBoxList1 do for idx := 0 to -1 + Items.Count do begin if Items[idx].Selected then sel := sel + String.Format('{0} : {1}{2}', Items[idx].Value, Items[idx].Text, '<br>'); end; Label1.Text := sel; end; end; //Page_Load

8. Run the project, and "play" with it...

   

Both the RadioButtonList and the CheckBoxList with their Items property provide enough methods and properties to easily iterate through the list and decide on page actions depending on the item(s) being selected.

Attributes don't render?!
Even though we have not yet discussed the Attributes property of a web control, developers already experimenting with ASP.NET might break their heads trying to add a simple "onclick" attribute to an item of a CheckBoxList (for example).
When you use the CheckBoxList (or RadioButtonList) Web Server ASP.NET control, if you try to add custom attributes to an Item, the key-value pairs are not rendered to the result page. Here's how to fix this behavior: CheckBoxListItemAttributes Web Control.

Before we finish this chapter we have to introduce two more selection controls: the ListBox and the DropDownList.

Next page > ListBox, DropDownList > Page 1, 2, 3

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