Subclassing new portlets

Portlet subclassing is not trivial due to explict references between portlet engine parts. Here are short instructions minimal steps to needed to a subclass a portlet to another portlet. Instead of modifying the existing portlet, we need to create a new invariant with little changed properties. See this general briefing about Plone 3.x portlet mechanism. This example modifies the render behavior of static text portlet, by adding a grey backgroundd CSS class for it.

1. Create a portlet interface stub and portlets Python module: To define a new portlet. Refer this in your product ZCML.
2. Create a new assigment class: To make new portlet assignable through portlet manager
3. Create a new add form class: To make new portlet creatable, returning your custom portlet instances
4. Create a configure.xml ZCML entry: To make Zope to find the new portlet definition
5. Create a portlets.xml installer entry: To make the portlet appear in the portlet manager menu

The portlet interface class is fixed to a portlet when the portlet is created. Thus, if you make changes any of above, you might need to create a new portlet to see the effect - old portlet instances don't necessarily see the changees.

Our portlet code lies in myproduct/browser/portlets/misc.py:

from zope.interface import implements
from Products.Five.browser.pagetemplatefile import ViewPageTemplateFile
from plone.portlet.static import PloneMessageFactory as _

# Import the base portlet module whose properties we will modify
from plone.portlet.static import static

class IGreyStaticPortlet(static.IStaticPortlet):
    """ Defines a new portlet "grey static" which takes properties of the existing static text portlet. """
    pass

class GreyStaticRenderer(static.Renderer):
    """ Overrides static.pt in the rendering of the portlet. """
    render = ViewPageTemplateFile('grey_static.pt')

class GreyStaticAssignment(static.Assignment):
    """ Assigner for grey static portlet. """
    implements(IGreyStaticPortlet)

class GreyStaticAddForm(static.AddForm):
    """ Make sure that add form creates instances of our custom portlet instead of the base class portlet. """
    def create(self, data):
        return GreyStaticAssignment(**data)

myproduct/browser/portlets/configure.zcml snippet. Note that we do not need to override all (EditForm) views:

<configure xmlns="http://namespaces.zope.org/zope"
           xmlns:browser="http://namespaces.zope.org/browser"
           xmlns:plone="http://namespaces.plone.org/plone">

    <include package="plone.app.portlets" />

        <plone:portlet
        name="lsm.GreyStaticPortlet"
        interface=".misc.IGreyStaticPortlet"
         assignment=".misc.GreyStaticAssignment"
         view_permission="zope2.View"
         edit_permission="cmf.ManagePortal"
         renderer=".misc.GreyStaticRenderer"
         addview=".misc.GreyStaticAddForm"
         editview="plone.portlet.static.static.EditForm"
         />

</configure>

myproducts/profiles/default/portlets.xml quick installer snippet:

<portlets>

  <portlet
    addview="lsm.GreyStaticPortlet"
    title="Static portlet (grey)"
    description="Portlet with light grey background"
    />

</portlets>

myproduct/browser/portlets/grey_static.pt. We have added one new CSS class (portletGrey) which has a CSS class definition defined in ploneCustom.css (through-the-web) or some of the product's CSS files:

<div tal:condition="view/data/omit_border"
     tal:attributes="class string:portletStaticText ${view/css_class}"
     tal:content="structure view/data/text" />
<dl tal:condition="not:view/data/omit_border"
    tal:attributes="class string:portlet portletStaticText portletGrey ${view/css_class}"
    i18n:domain="plone">

    <dt class="portletHeader">
        <span class="portletTopLeft"></span>
        <span>
           <a tal:omit-tag="not:view/has_link"
              tal:attributes="href view/data/more_url"
              tal:content="view/data/header"
              />
        </span>
        <span class="portletTopRight"></span>
    </dt>

    <dd class="portletItem odd">
        <div tal:replace="structure view/data/text" />
        <tal:corners condition="not:view/has_footer">
            <span class="portletBottomLeft"></span>
            <span class="portletBottomRight"></span>
        </tal:corners>
    </dd>

    <dd class="portletFooter" tal:condition="view/has_footer">
        <span class="portletBotomLeft"></span>
        <span>
           <a tal:omit-tag="not:view/has_link"
              tal:attributes="href view/data/more_url"
              tal:content="view/data/footer"
              />
        </span>
        <span class="portletBottomRight"></span>
    </dd>

</dl>

myproduct/browser/portlets/__init__.py. Create empty file to a mark a Python module.

myproduct/configure.zcml. Add following snippet:

<include package=".portlets" />