RenderBlock

Renders the body of a Block component, which may be selected dynamically. The Block may be on the same page as the RenderBlock or on another page entirely.

Warning:

The PageBeginRenderListener (and PageEndRenderListener ) event notications only go to the active page (the active page is the page that renders the response). It is possible to pass a Block from an entirely different page to a RenderBlock, but render listeners of both types on the non-active pages will not be notified.

See also: org.apache.tapestry.components.RenderBlock , Block

Parameters

Name Type Required Default Description
block Block yes The Block to render.

Body: removed

Informal parameters: allowed

Reserved parameters: none

Informal parameters are allowed, but are not used by the RenderBlock component. Instead, they are used to pass information to the Block itself. The Block's invoker property will be the RenderBlock that invokes it (in 3.0, this property was called "inserter", which is maintained for backwards compatibility). The parameters of the RenderBlock are available via the getParameter() method of Block . This is most useful when the RenderBlock and Block are contained within different components or even different pages.

Example

This example shows a page with a custom TabPanel component. When a user selects a tab, TabPanel switches content. Each tab content is defined by a Block. The final result shows a tab view that highlights the currently selected tab:

RenderBlock Screen Shot

First we'll show a page that makes use of the TabPanel component.

TabTest.html:

<html jwcid="@Shell" title="TabPanel Test">
  <body>
  <span jwcid="@TabPanel" blockIds="ognl:{'berlin', 'rome', 'tokyo'}" selectColor="#FFFF00" unSelectColor="#CCFFFF" borderColor="#00CC33"/>

  <span jwcid="berlin@Block">
    <h1>Berlin</h1>
  </span>

  <span jwcid="rome@Block">
    <h1>Rome</h1>
  </span>

  <span jwcid="tokyo@Block">
    <h1>Tokyo</h1>
  </span>
  </body>
</html>

For simplicity, this example uses an engineered naming coincidence : the names of the Block components matches the localized message key used to obtain the title. In this case, the Blocks contain just a snippet of HTML ... but they could contain any valid markup, including components, links, forms, or other complex components. The use of OGNL makes it easy to assemble a list of strings, the component ids for the Blocks, and pass that list into the TabPanel component.

TabTest.properties:

berlin=Berlin
rome=Rome
tokyo=Tokyo

Most of the interesting parts, including the use of the RenderBlock component, occurs inside the TabPanel component specification and template.

TabPanel.html:

<table border="0" width="50%" cellspacing="0" cellpadding="0">
  <tr>
    <td width="10">&nbsp;</td>
    <td>
      <table border="0" cellspacing="0" cellpadding="5">
        <tr>
          <span jwcid="loop">
            <td jwcid="tab">
              <a jwcid="link">
                <span jwcid="@Insert" value="ognl:container.messages.getMessage(blockId)">Tab Title</span>
              </a>
            </td>
            <td width="1"></td>
          </span>
        </tr>
      </table>
    </td>
    <td width="10">&nbsp;</td>
  </tr>
  <tr>
    <td jwcid="@Any" height="5" bgcolor="ognl:borderColor" colspan="3">&nbsp;</td>
  </tr>
  <tr>
    <td jwcid="@Any" width="10" bgcolor="ognl:borderColor">&nbsp;</td>
    <td align="center">
      <span jwcid="@RenderBlock" block="ognl:selectedBlock">Page content goes here</span>
    </td>
    <td jwcid="@Any" width="10" bgcolor="ognl:borderColor">&nbsp;</td>
  </tr>
  <tr>
    <td jwcid="@Any" height="5" bgcolor="ognl:borderColor" colspan="3">&nbsp;</td>
  </tr>
</table>

The key concepts shown here are:

  • The loop component, which iterates over the blockIds parameter (a List of strings), setting the blockId property on each pass
  • The @ Insert component, which users the current blockId to look up a localized message in the TabPanel component's container (the TabTest page)
  • The RenderBlock component, which uses the component's selectedBlock property to determine what Block to actually render
  • The use of the @ Any component to render several <td> elements with the current bgcolor attribute.
Several of the details are filled out in the component specification. TabPanel.jwc: 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE component-specification
  PUBLIC "-//Apache Software Foundation//Tapestry Specification 4.0//EN"
  "http://tapestry.apache.org/dtd/Tapestry_4_0.dtd">

<component-specification class="com.example.components.TabPanel" allow-body="no" allow-informal-parameters="no">

  <property name="selectedBlockId" persist="session"/>

  <parameter name="blockIds" required="yes"/>
  <parameter name="borderColor" required="yes"/>
  <parameter name="selectColor" default-value="#7D000D"/>
  <parameter name="unSelectColor" default-value="#C0C0C0"/>

  <component id="loop" type="Foreach">
    <binding name="source" value="blockIds"/>
    <binding name="value" value="blockId"/>
  </component>
  
  <component id="tab" type="Any">
    <binding name="bgcolor">
      tabSelected ? selectColor : unSelectColor
    </binding>
  </component>
      
  <component id="link" type="DirectLink">
    <binding name="listener" value="listener:doClick"/>
    <binding name="parameters" value="blockId"/>
    <binding name="disabled" value="tabSelected"/>
  </component>
</component-specification>
Several bindings in the specification depend on the tabSelected property, which is a synthetic property calculated in Java code. In addition, the @ DirectLink component is configured to pass the block id in the URL as a listener parameter. TabPanel.java: 
package com.example.components;

import org.apache.tapestry.BaseComponent;
import org.apache.tapestry.components.Block;

import java.util.List;

public abstract class TabPanel extends BaseComponent
{
    // Persistent
    public abstract String getSelectedBlockId();
    public abstract void setSelectedBlockId(String id);

    public abstract List getBlockIds();

    // Current block id within the loop
    public abstract String getBlockId();
    
    public Block getSelectedBlock()
    {
      String selectedId = getSelectedBlockId();
      
      if (selectedId == null)
        selectedId = (String) getBlockIds().get(0);
        
      return (Block) getContainer().getComponent(selectedId);   
    }

    public boolean isTabSelected()
    {
      String selectedId = getSelectedBlockId();
      
      if (selectedId == null)
        selectedId = (String) getBlockIds().get(0);
        
      return getBlockId().equals(selectedId);
    }

    public void doClick(String selectedId) 
    {
      setSelectedBlockId(selectedId);
    }
}

The only major trick here is that initially the persistent selectedBlockId property will be null, and we have to work around it by treating the first element in the blockIds parameter as the default selectedBlockId. The doClick() listener method is very simple; the blockId that was passed in the URL is obtained and used to update the selectedBlockId property, which was declared persistent in the specification.

Note that we don't store the Block instance as a persistent property ... components are not serializable and should never be stored as persistent properties. We store the id needed to locate the Block .