print barcode labels vb.net The JSF Event Model in Java

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The JSF Event Model
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<h:inputText valueChangeListener="#{backing_beanvalueChangeMethod}"/>
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When the application is run and a value is entered into the input field and the form is submitted by clicking on the button, the valueChangeMethod( ) will be executed because the value of the input field was changed from its initial empty value to a new value with the entered text However, unlike the action event in which the event is processed during the Invoke Application phase, value change events are processed in the Process Validations phase A subsequent re-submission of the form without changing the value in the input field will not cause the value change listener method to execute You can cause the value of an input component to be set immediately, before any other input components during the Apply Request Values phase, by setting its immediate attribute to true This is needed in certain cases to avoid validation errors when processing value change events You will see an example of this later in the chapter
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PART I PART I PART I
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Writing Custom Action and Value Change Listeners
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So far you have seen how to write methods that use the default action and value change listeners These methods were directly associated with UI components by using their action or actionlistener JSP tag attributes, like this:
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<h:commandButton value="Confirm" action="#{UserBeanaddConfirmedUser}" />
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or like this:
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<h:commandButton value="Confirm" actionlistener="#{UserBeanaddConfirmedUser}" />
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In addition to using the default listeners, you can write your own action or value change listener classes These classes simply implement either the ActionListener or ValueChangeListener interface The following code is an example of a simple custom action listener class Notice the processAction( ) method that is overridden to process the actual action event
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package comjsfcompref; import javaxfaceseventActionListener; import javaxfaceseventActionEvent; public class MyActionListener implements ActionListener { public MyActionListener() { } public void processAction(ActionEvent ae) { Systemoutprintln("MyActionListener is processing an action event!"); } }
To use the custom action listener class, MyActionListener, you can associate it with a UI component using a nested <f:actionlistener /> tag as follows
<h:commandButton value="Click Me!"> <f:actionListener type="comjsfcomprefMyActionListener"/> </h:commandButton>
Part I:
The JavaServer Faces Framework
Notice that in this case the action listener tag uses the type attribute to refer directly to the full Java classpath of the custom action listener As expected, when this page is run and when the button is clicked, the processAction( ) method will execute and print a message to the console
NOTE There is a slight limitation with this usage in that there is no ability to configure the
actionListener instance, as it will just be created with default arguments It is possible, however, to create a custom actionListener and package it into a reusable JSP tag that exposes its initialization arguments Oracle s ADF Faces, which is covered in Appendix B, actually provides the af:setActionListener tag that provides this In a similar fashion, a custom value change listener class that implements the ValueChangeListener interface could also be created like this:
package comjsfcompref; import javaxfaceseventValueChangeListener; import javaxfaceseventValueChangeEvent; public class MyValueChangeListener implements ValueChangeListener { public MyValueChangeListener() { } public void processValueChange(ValueChangeEvent vce) { Systemoutprintln("MyValueChangeListener is processing a value change event!"); } }
To use the custom value change listener MyValueChangeListener class, you can associate it with any UI component that holds a value using a nested <f:valueChangelistener /> tag as follows
<h:inputText value="foo" "> <f:valueChangeListener type="comjsfcomprefMyValueChangeListener"/> </h:inputText> <h:commandButton value="Click me!"/>
Similar to the action listener tag, valueChangeListener also uses a type attribute to refer directly to the value change listener class using its full Java classpath When the page containing this code is run, the user can then change the current value (from foo ) in the input field and click on the submit button to issue a postback request During the Apply Request Value phase of the request processing lifecycle, the Faces runtime will see that the value of the input field was changed between the initial and postback request and MyValueChangeListener s The processValueChange( ) method will execute and print a message to the console Many times it is useful to submit a form without requiring the user to click on a submit button For example, consider the situation in which you want to auto-fill the city and state after a user has entered a Zip code In this case, setting the JavaScript callout onchange attribute of the Zip Code input field to thisformsubmit( ) will cause the form to be
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