Module org.apache.wicket.extensions
Package org.apache.wicket.extensions.ajax.markup.html

Class AjaxLazyLoadPanel<T extends Component>

java.lang.Object
org.apache.wicket.Component
org.apache.wicket.MarkupContainer
org.apache.wicket.markup.html.WebMarkupContainer
org.apache.wicket.markup.html.panel.Panel
org.apache.wicket.extensions.ajax.markup.html.AjaxLazyLoadPanel<T>
All Implemented Interfaces:
Serializable, Iterable<Component>, IEventSink, IEventSource, IFeedbackContributor, IConverterLocator, IMetadataContext<Serializable,Component>, IQueueRegion, IHeaderContributor, IRequestableComponent, IHierarchical<Component>, IClusterable
public abstract class AjaxLazyLoadPanel<T extends Component> extends Panel
A panel which load lazily a single content component. This can be used if you have a component that is pretty heavy in creation and you first want to show the user the page and then replace the panel when it is ready.

This panel will wait with adding the content until isContentReady() returns true. It will poll using an AbstractAjaxTimerBehavior that is installed on the page. When the component is replaced, the timer stops. When you have multiple AjaxLazyLoadPanels on the same page, only one timer is used and all panels piggyback on this single timer.

This component will also replace the contents when a normal request comes through and the content is ready.

Since:
1.3
See Also:

  • Constructor Details

  • Method Details

    • isContentReady

      protected boolean isContentReady()
      Determines that the content we're waiting for is ready, typically used in polling background threads for their result. Override this to implement your own check.

      This default implementation returns true, i.e. assuming the content is ready immediately.

      Returns:
      whether the actual content is ready

    • getLoadingComponent

      public Component getLoadingComponent(String id)
      Create a loading component shown instead of the actual content until it is isContentReady().
      Parameters:
      id - The components id
      Returns:
      The component to show while the real content isn't ready yet

    • getLazyLoadComponent

      public abstract T getLazyLoadComponent(String markupId)
      Factory method for creating the lazily loaded content that replaces the loading component after isContentReady() returns true. You may call setRenderBodyOnly(true) on this component if you need the body only.
      Parameters:
      markupId - The components markupid.
      Returns:
      the content to show after isContentReady()

    • onContentLoaded

      protected void onContentLoaded(T content, Optional<AjaxRequestTarget> target)
      Called after the loading component was replaced with the lazy loaded content.

      This default implementation does nothing.

      Parameters:
      content - The lazy loaded content
      target - optional Ajax request handler

    • onBeforeRender

      protected void onBeforeRender()
      Installs a page-global timer if not already present.
      Overrides:
      onBeforeRender in class Component
      See Also:

    • initTimer

      protected void initTimer()
      Initialize a timer - default implementation installs an AbstractAjaxTimerBehavior on the page, if it is not already present.

    • onConfigure

      protected void onConfigure()
      Description copied from class: Component
      Called on all components before any component is rendered. This method should be used to configure such things as visibility and enabled flags.

      Overrides must call super.onConfigure(), usually before any other code

      NOTE: Component hierarchy should not be modified inside this method, instead it should be done in Component.onBeforeRender()

      NOTE: Why this method is preferrable to directly overriding Component.isVisible() and Component.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.

      NOTE: If component's visibility or another property depends on another component you may call other.configure() followed by other.isVisible() as mentioned in Component.configure() javadoc.

      NOTE: Why should Component.onBeforeRender() not be used for this? Because if a component's visibility is controlled inside Component.onBeforeRender(), once invisible the component will never become visible again.

      Overrides:
      onConfigure in class Component

    • getUpdateInterval

      public Duration getUpdateInterval()
      Get the preferred interval for updates.

      Since all LazyLoadingPanels on a page share the same Ajax timer, its update interval is derived from the minimum of all panel's update intervals.

      Returns:
      update interval, must not be null

    • isLoaded

      public final boolean isLoaded()
      Check whether the content is loaded.

      If not loaded already and the content is ready, replaces the lazy loading component with the lazily loaded content.

      Returns:
      true if content is loaded
      See Also: