Apple WebObjects 3.5 Manuel d'utilisateur télécharger pdf (Page 138)

Chapter 7 Managing State

138

pageWithName: and Page Caching

When the application object receives a pageWithName: message, it creates a new

component. For example, in the HelloWorld example a user enters a name in

the ﬁrst page (the Main component), clicks Submit, and is presented with a

personal greeting on the second page (the Hello component). Clicking the

Submit button in the ﬁrst page invokes the

sayHello method in the Main

component. As part of its implementation

sayHello sends a pageWithName: message to

the application object:

// Java HelloWorld

String visitorName;

public Component sayHello() {

//Create the next page

Hello nextPage = (Hello)application().pageWithName("Hello");

// Set state in the Hello page

nextPage.setVisitorName(visitorName);

// Return the Hello page

return nextPage;

}

Each time the sayHello method is invoked, a new Hello component is created. For

example, if the user backtracks to the main page and clicks the Submit button

again, another Hello page is created. It’s unlikely this duplication of components

will be a problem for the HelloWorld application, since users quickly tire of its

charms. But, depending on design, some applications may beneﬁt by modifying

the operation of

pageWithName: so that an existing component can be reused.

If you want to extend WebObjects’ page caching mechanism to include pages

returned by

pageWithName:, you must implement your own solution. Fortunately,

it’s easy. One approach is to have the session maintain a dictionary that maps

page names to page objects. Here’s the code you would add to the session

object:

// example Session.java

MutableHashtable pageDictionary;

public Session() {

super();

pageDictionary = new MutableHashtable();

}

public Component pageWithName(String aName) {

return (Component)pageDictionary.get(aName);

}

public void storePage(String aName, Component aPage) {

pageDictionary.put(aName, aPage)

}

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Apple WebObjects 3.5 Manuel d'utilisateur Page 138

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