selection

The selection input elements provide means of choosing amongst predetermined list of items.

However, there are some special issues involving selection elements. The first of which has to do with the fact they involve multiple bindings, one for the selected items, and one or more for the options to be selected from.

The dWebSpec types involved in selections are radioGroup, checkboxGroup, select and radio type elements. These are shown in the table below.

The first one, checkbox, is not a selections element, it as input elements that allows for true/false entries; it is included here because of the relationship with the checkboxGroup.

The radio input allow selection of one of multiple options, as such, standalone it is of no use. When included multiple times within a form, with each instance bound to different singular value, but all instances sharing an identifier, they in essence form a radio group.

The radioGroup would be bound to a collection of options, with which it would render the member radio buttons with a singular value identifier. In short the difference between the radio and radioGroup, is that the earlier allows fine grain binding of values to individual radio elements, whereas the values for radioGroup would come from a collection.

The checkboxGroup is similar to the radioGroup, in that it would be bound to a collection of options, with which it would render the member checkboxes with a single identifier. However, it could allow single or multiple selections; the latter would imply that selected values would be returned as collection. The select element has identical binding structure with the checkboxGroup.

The list of elements of the select type is shown in the table below.

The select category elements are basically input elements that allow selection from a predetermined list rather than user entry.

As such they share the same basics as the input type. Please refer to the input type for the basics.

Where the select items differ is that they would be associated with options or option type element as shown below.

Example implementation is shown below.

  <asp:DropdownList id="CustomerID" runat="server" 
       DataSourceID="CustomersDS"          
       DataTextField="CustomerName"          
       DataValueField ="CustomerID" />

The options element properties are reflected directly on the properties of the select type elements, on the ASP.NET platform. This subtle difference should be noted. In HTML options elements are nested in the select element, and not its property. This is the way it is also modeled in dWebSpec and most platforms.

The mapping of the options to the attribute of the select controls is shown below.

The list item specification and mapping is shown above, the table below shows the full set of attributes shared by list controls and their mappings. These mappings are to the element descriptor attributes, except otherwise stated.

Option

Unlike the implementation of the options type element that is merged with that of the associated select element, the implementation of the option type is separate.

An example specification would appear as follows.

This would be implemented as:

  <asp:ListItem Text="{#Eval('CustopmerName'}" Value="{#Eval('CustopmerID'}" />

The dynamically populated list items would show up in the descriptors as shown in the example above. However, there could be static options in the source content; example is shown below.

<option Value="" >Please select an item</option>

The implementation for these would be as shown below.

  <asp:ListItem Value="">Please select an item</asp:ListItem>

Other List Items Implementation Attributes.

Most of the standard elements have direct correspondence to HTML elements. It is the elements of the component category that do not have direct correspondence to single HTML element. They could include multiple elements, layout and segments.

In the selection category, the checkboxGroup and radioGroup are also of the component category; they do not have correspondence to an HTML element, furthermore they could include template or layout code.

Notwithstanding, their implementation on most platform could be simplified into simple repetition of single element (e.g. checkbox), plus additional attribute to indicate horizontal or vertical layout. ASP.NET provided for these additional parameters, as highlighted in the table below.