8.4 The class hierarchy for DUIM-Gadgets

8.4.2 Subclasses of <value-gadget>

Any gadget that can take a value of some sort is a subclass of <value-gadget>. As might be expected, this includes the majority of the gadgets in the DUIM-Gadgets library.

Every subclass of <value-gadget> supports the value protocol, as described in Section 8.1 on page 503.

Several subclasses of <value-gadget> themselves have a number of subclasses defined. These include:

<text-gadget>: Any gadget into which you can type text. These include both text editors (multiple line edit controls) and text fields (single line edit controls).
<value-range-gadget>
: Value gadgets whose value can vary within a known range, such as scroll bars.
<button>: Any button, such as a radio button, check button, or push button. See Section 8.4.4 on page 514 for more details about the classes of button available.
<collection-gadget>
: Any gadget whose contents form a collection, such as a list, a tree control, or a group of buttons. See Section 8.4.5 on page 515 for more details about the classes of collection gadget available.

Also provided are the following specific GUI elements:

<menu-bar>: This used to create the standard menu bar that is commonly found across the top of an application frame.
<status-bar>: This is used to create a status bar, usually placed at the bottom of an application frame. A status bar is used to display miscellaneous information about the current state of the application.
<tab-control>: Tab controls are analogous to dividers in a filing cabinet or notebook, with multiple logical pages of information displayed within the same window. Clicking on any of the tabs displayed in a tab control displays a new page of information.

The subclasses of <value-gadget> are as shown in Table 8.2.

Table 8.2 Subclasses of the `<value-gadget>` class
<value-gadget>
	<text-gadget>
		<password-field>
		<text-editor>
		<text-field>
	<value-range-gadget>
		<slider>
		<scroll-bar>
		<progress-bar>
	<button>	See Section 8.4.4
	<menu-bar>
	<status-bar>
	<tab-control>
	<collection-gadget>	See Section 8.4.5