another new callback added to 1.4/trunk that is aimed at making life
easier when managing component states such as visibility, enabled,
etc.
/**
* Called once per request on components before they are about to be
rendered. This method
* should be used to configure such things as visibility and enabled
flags.
* <p>
* Overrides must call {...@code super.onInitialize()}, usually before
any other code
* </p>
* <p>
* NOTE: Component hierarchy should not be modified inside this
method, instead it should be
* done in {...@link #onBeforeRender()}
* </p>
* <p>
* NOTE: Why this method is preferrable to directly overriding {...@link
#isVisible()} and
* {...@link #isEnabled()}? Because those methods are called multiple
times even for processing of
* a single request. If they contain expensive logic they can slow
down the response time of the
* entire page. Further, overriding those methods directly on form
components may lead to
* inconsistent or unexpected state depending on when those methods
are called in the form
* processing workflow. It is a better practice to push changes to
state rather than pull.
* </p>
* <p>
* NOTE: If component's visibility or another property depends on
another component you may call
* {...@code other.configure()} followed by {...@code
other.isVisible()} as
mentioned in
* {...@link #configure()} javadoc.
* </p>
* <p>
* NOTE: Why should {...@link #onBeforeRender()} not be used for this?
Because if visibility of a
* component is toggled inside {...@link #onBeforeRender()} another
method needs to be overridden
* to make sure {...@link #onBeforeRender()} will be invoked on ivisible
components:
*
* <pre>
* class MyComponent extends WebComponent
* {
* protected void onBeforeRender()
* {
* setVisible(Math.rand() > 0.5f);
* super.onBeforeRender();
* }
*
* // if this override is forgotten, once invisible component will
never become visible
* protected boolean callOnBeforeRenderIfNotVisible()
* {
* return true;
* }
* }
* </pre>
*
* VS
*
* <pre>
* class MyComponent extends WebComponent
* {
* protected void onConfigure()
* {
* setVisible(Math.rand() > 0.5f);
* super.onConfigure();
* }
* }
* </pre>
*/
protected void onConfigure()
{
}
/**
* Triggers {...@link #onConfigure()} to be invoked on this component if
it has not already during
* this request.
* <p>
* This method should be invoked before any calls to {...@link
#isVisible()} or
* {...@link #isEnabled()}. Usually this method will be called by the
framework before the
* component is rendered and so users should not need to call it;
however, in cases where
* visibility or enabled or other state of one component depends on
the state of another this
* method should be manually invoked on the other component by the
user. EG to link visiliby of
* two markup containers the following should be done:
*
* <pre>
* final WebMarkupContainer source=new WebMarkupContainer("a") {
* protected void onConfigure() {
* setVisible(Math.rand()>0.5f);
* }
* };
*
* WebMarkupContainer linked=new WebMarkupContainer("b") {
* protected void onConfigure() {
* source.configure(); // make sure source is configured
* setVisible(source.isVisible());
* }
* }
* </pre>
*
* </p>
*/
public final void configure()
{
if (!getFlag(FLAG_CONFIGURED))
{
onConfigure();
setFlag(FLAG_CONFIGURED, true);
}
}
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