Breadcrumbs (path bar)

Description

Breadcrumbs is visual element showing where the user is on the site. This document shows some example code how to create breadcrumbs programmatically.

Navigation level sensitive breadcrumbs

Below is a breadcrumbs viewlet displayed only on 3rd navigation level downwards. Drop this in your add-on template. Tune the visible() function for further functionality.

Python code to be dropped in viewlets.py:

from plone.app.layout.viewlets.interfaces import IAboveContent


class Breadcrumbs(grok.Viewlet):
    """ Breadcrumbs override which are only displayed on 2nd level and forward (not on Home screen)
    """

    # Override standard Plone breadcrumbs
    grok.name("plone.path_bar")
    grok.viewletmanager(IAboveContent)

    def visible(self):
        """ Called by template condition. """

        # Note that "Home" does not count as a crumb
        return len(self.breadcrumbs) >= 1

    def update(self):
        context= self.context.aq_inner

        self.portal_state = getMultiAdapter((context, self.request), name="plone_portal_state")
        self.site_url = self.portal_state.portal_url()
        self.navigation_root_url = self.portal_state.navigation_root_url()

        breadcrumbs_view = getMultiAdapter((context, self.request), name='breadcrumbs_view')
        self.breadcrumbs = breadcrumbs_view.breadcrumbs()

        # right-to-left reading order
        self.is_rtl = self.portal_state.is_rtl()

Template code templates/breadcrumbs.pt:

<div id="portal-breadcrumbs"
     i18n:domain="plone"
     tal:condition="viewlet/visible"
     tal:define="breadcrumbs viewlet/breadcrumbs;
                 is_rtl viewlet/is_rtl">

    <span id="breadcrumbs-home">
        <a i18n:translate="tabs_home"
           tal:attributes="href viewlet/navigation_root_url">Home</a>
        <span tal:condition="breadcrumbs" class="breadcrumbSeparator">
            <tal:ltr condition="not: is_rtl">|</tal:ltr>
            <tal:rtl condition="is_rtl">|</tal:rtl>
        </span>
    </span>
    <span tal:repeat="crumb breadcrumbs"
          tal:attributes="dir python:is_rtl and 'rtl' or 'ltr';
                          id string:breadcrumbs-${repeat/crumb/number}">
        <tal:item tal:define="is_last repeat/crumb/end;
                              url crumb/absolute_url;
                              title crumb/Title">
            <a href="#"
               tal:omit-tag="not: url"
               tal:condition="python:not is_last"
               tal:attributes="href url"
               tal:content="title">
                crumb
            </a>
            <span class="breadcrumbSeparator" tal:condition="not: is_last">
                <tal:ltr condition="not: is_rtl">|</tal:ltr>
                <tal:rtl condition="is_rtl">|</tal:rtl>
            </span>
            <span id="breadcrumbs-current"
                  tal:condition="is_last"
                  tal:content="title">crumb</span>
         </tal:item>
    </span>

</div>

Back button

Below is an example how we have extracted information like the parent container and such from breadcrumbs.

Note

We need special dealing for "default view" of objects... that's the canonical part.

class Back(grok.Viewlet):
    """ Back button
    """

    def update(self):
        context= aq_inner(self.context)

        context_helper = getMultiAdapter((context, self.request), name="plone_context_state")

        portal_helper = getMultiAdapter((context, self.request), name="plone_portal_state")

        canonical = context_helper.canonical_object()

        parent = aq_parent(canonical)

        breadcrumbs_view = getView(self.context, self.request, 'breadcrumbs_view')
        breadcrumbs = breadcrumbs_view.breadcrumbs()

        if (len(breadcrumbs)==1):
            self.backTitle = _(u"Home")
        else:
            if hasattr(parent, "Title"):
                self.backTitle = parent.Title()
            else:
                self.backTitle = _(u"Back")

        if hasattr(parent, "absolute_url"):
            self.backUrl = parent.absolute_url()
        else:
            self.backUrl = portal_helper.portal_url()

        self.isHome = len(breadcrumbs)==0

More info

• http://code.google.com/p/plonegomobile/source/browse/gomobiletheme.basic/trunk/gomobiletheme/basic/viewlets.py#281