Collecting RadioButtonList Controls in VS .NET

Creator QR-Code in VS .NET Collecting RadioButtonList Controls

The ASPNET RadioButtonList control allows you to create many radio buttons with one control In this section, you build a survey form, work with the Collection editor, and hook up an event handler

The survey interface consists of a prompt, a set of radio buttons as choices, a button, and an area for a response Follow these steps to create the basic interface 1 In the ASPNET page Design view, add a Label control with the ID lblPrompt and set the Text value to Rate Your Fear of the Borg 2 From the Toolbox, drop a RadioButtonList control on the design surface and set its ID to rblBorg 3 Add another Label with the ID lblResponse and a Button control

Think of a game of Bingo where players are filling their cards with markers Suddenly, a hand shoots into the air and a player shouts, Bingo! That s an event Consider the player with the filled card as an ASPNET control that raises an event called Bingo The game s assistants are event handlers who intervene when someone claims to have a full card The following pseudo-code (unusable code that represents a programming idea) shows how you might handle a Bingo event Protected Sub BingoPlayer1_Bingo _ (ByVal player As Object, _ ByVal e As _ SystemBingoEventArgs) Dim blnIsValidBingo as _ boolean Dim walker as New _ Assistant() blnIsValidBingo = _ walkerVerify(eCard) End Sub In ASPNET, when someone clicks a button, the button doesn t shout, Bingo! It raises a Click event If no code is on the page to handle the event, nothing much happens However, if a designated event handler for the mouse click is on the page, the handler subroutine goes into action That action could be changing a label s color from blue to red or sending the accumulated data to a database

You can add items to a RadioButtonList control at design-time by using a designer called Collection editor Collection editors mostly work alike, regardless of the collection type Follow these steps to design options for a questionnaire: 1 Click the RadioButtonList control s Smart Tag arrow, and from the menu, choose Edit Items The ListItem Collection editor opens 2 Click the Add button (on the lower-left side) As shown in Figure 5-3, ListItem appears in the Members area on the left Notice the 0 preceding the ListItem The first item in a NET collection is numbered zero See the The Borg and NET collections sidebar for more 3 In the properties area on the right, set the Text value to Plenty and the Value property to 3

Figure 5-3: A collection editor allows you to add, remove, and change individual items within a collection

4 Add three more items to the collection and set their Text and Value properties as follows: Text Somewhat Whatever Zilch Value 2 1 0

5 Click OK to close the ListItem Collection editor As shown in Figure 5-4, the user interface elements are in place In the next section, you add some logic and interactivity

So far, the survey form is just a (Vulcan-like) interface with no logic Follow these steps to capture the user s choice and show that choice in the browser:

Fans of the science fiction series Star Trek know all about the Borg, those gray technoinvaders who wander around muttering, Resistance is futile A NET collection resembles The Borg Collective in that items within a collection are similar but have distinguishing characteristics (such as different machine parts) You deal with members of a collection as a set or group Your code can examine each member one by one from first to last In geekspeak, the action of flipping through the set is iterating through a collection The For Each loop is frequently used to give collections an efficient once-over Like you can with cyborgs, you can refer to members of a NET collection by an index number that reflects their position within the collective, er collection One notable thing about collections in NET is that their numbering is zero-based That means the index number of the first item is 0 The index number of the second item is 1 Imagine the chaos within the Borg Collective when you infuse it with the knowledge that Seven of Nine is actually a Six of Nine in NET s zero-based counting

1 In Design view, double-click an empty part of the page to create an event handler for the Page object s Load event The IDE automatically inserts the following event handler code (formatted differently here) into the page: Protected Sub Page_Load(ByVal sender As Object, _ ByVal e As SystemEventArgs) End Sub 2 In the line above the End Sub keywords, insert the following code: lblResponseText = rblBorgSelectedValue When you run the page and click the button, the click causes the page to submit its data (a postback) A Page Load event occurs (fires in geekspeak) just before ASPNET completes construction of the page The Load event handler code looks at the RadioButtonList (rblBorg) and extracts whatever is in its SelectedValue property The code assigns the SelectedValue value as the Text property of the Label so the user can see the results