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Chapter 6 Creating Reusable Components

the World Wide Web Wisdom company could change the look of the

navigational controls in all of its applications by changing this one component.

If your application’s pages are highly structured, reusable components could be

the prevailing feature of each page:

<HTML>

<HEAD>

<TITLE>World Wide Web Wisdom, Inc.</TITLE>

</HEAD>

<BODY>

</BODY>

</HTML>

The corresponding declarations ﬁle might look like this:

HEADER: CorporateHeader {};

PRODUCTDESCRIPTION: ProductTable {productCode = "WWWW0314"};

NAVCONTROL: NavigationControl {};

FOOTER: Footer {type = "catalogFooter"};

Notice that some of these components above take arguments—that is, they are

parameterized. For example, the ProductTable component’s

productCode attribute

is set to a particular product identiﬁer, presumably to display a description of

that particular product. The combination of reusability and customizability is

particularly powerful, as you’ll see in the next section.

Simplifying Interfaces

Another beneﬁt of reusable components is that they let you work at a higher

level of abstraction than would be possible by working directly with HTML

code or with WebObjects’ dynamic elements. You (or someone else) can create

a component that encapsulates a solution to a possibly complicated

programming problem, and then reuse that solution again and again without

having to be concerned with the details of its implementation. Examples of this

kind of component include:

•A menu that posts different actions depending on the user’s choice

•A calendar that lets a user specify start and end dates

•A table view that displays records returned by a database query

To illustrate this feature, consider a simple reusable component, an alert panel

like the one shown in Figure 28.

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Apple WebObjects 3.5 Manual do Utilizador Página 96