About

In a CMS, it’s often very useful to be able to design and provide several views for a single item. These views can be relevant, according to a given context and situation. dolmen.app.viewselector allows you to define a view as being an “alternate” option to render a given context. A menu then provides you the machinery to select the most relevant view for your usecase.

A quick overview

To know that a component can provide alternative views, we need to explicitly specify it. An interface defines the “selector” capability:

>>> from dolmen.app.viewselector import IViewSelector
>>> list(IViewSelector)
['selected_view']

>>> IViewSelector['selected_view']
<...TextLine...>

The IViewSelector interface defines a single field, known as ‘selected_view’. The field value is merely the name of the Page component currently used:

>>> IViewSelector['selected_view'].default
u'base_view'

Out of the box, the default value is set to ‘base_view’.

Defining the content

To demonstrate the alternative views, we first need a context that is aware of the views selection:

>>> from zope.location import Location
>>> from zope.interface import implements

>>> class Bear(Location):
...  implements(IViewSelector)
...  selected_view = u"sleeping"

We defined the default view to the view named “sleeping”.

Defining alternate views

The alternative views are ‘pages’ (see megrok.layout and dolmen.app.layout) that are registered onto a dedicated menu. To define an alternative view, we inherit from the AlternativeView base class:

>>> import grokcore.view as grok
>>> from grokcore.component import testing
>>> from dolmen.app.viewselector import AlternativeView

>>> class Sleeping(AlternativeView):
...   grok.context(Bear)
...   grok.title("Sleeping bear")
...
...   def render(self):
...     return u"RRrrr..."

>>> testing.grok_component('sleeping', Sleeping)
True

The “sleeping” view that we defined as a default value for our IViewSelector is now defined and registered. Let’s register 2 other views, to populate the menu and provide a “realistic” usecase:

>>> class PolarFur(AlternativeView):
...   grok.context(Bear)
...   grok.title("Polar bear")
...
...   def render(self):
...     return u"I'm white !"

>>> testing.grok_component('polar', PolarFur)
True

>>> class SpringFur(AlternativeView):
...   grok.context(Bear)
...   grok.title("Spring bear")
...   grok.require("dolmen.content.Edit")
...
...   def render(self):
...     return u"I'm brown !"

>>> testing.grok_component('spring', SpringFur)
True

Default dynamic index

In order to render the selected view, another view is used. We may call it a “routing” view, as it’s used to lookup and render the desired component.

We first need to instance the two needed components, the content and the request

>>> from zope.publisher.browser import TestRequest

>>> herman = Bear()
>>> request = TestRequest()

The content provides IViewSelector, the interface for which the “routing” view is registered:

>>> IViewSelector.providedBy(herman)
True

The “routing” view is by convention called “index” and can be looked up as a basic view:

>>> from zope.component import getMultiAdapter
>>> index = getMultiAdapter((herman, request), name="index")
>>> index
<dolmen.app.viewselector.select.SelectedView...>

This view, when rendered, will look up and render the view named as the selected_view attribute, registered for the same content and request:

>>> herman.selected_view
u'sleeping'

>>> index.render()
u'RRrrr...'

If we set a different value for the selected_view attribute, the looked up view changes accordingly:

>>> herman.selected_view = u"polarfur"
>>> index.render()
u"I'm white !"

>>> herman.selected_view = u"springfur"
>>> index.render()
u"I'm brown !"

If the view doesn’t exist, a base message is returned:

>>> herman.selected_view = u"nothing"
>>> index.render()
u'The selected view is not a valid IPage component.'

Applying the view via the User interface

The selected view can be chosen from a list of available alternative view. This choice is made via a menu, for which the views are registered.

>>> from zope.component.hooks import getSite
>>> site = getSite()

>>> herman = site['herman'] = herman
>>> herman.__name__
u'herman'

>>> baseview = Sleeping(herman, request)

>>> from dolmen.app.layout.master import AboveBody
>>> from dolmen.app.viewselector.select import SelectableViews

>>> manager = AboveBody(herman, request, baseview)
>>> menu = SelectableViews(herman, request, baseview, manager)

>>> login('zope.user')

>>> menu.update()
>>> print menu.render()
<dl id="selectable-views" class="additional-actions">
  <dt>Content display</dt>
  <dd>
    <ul class="menu">
      <li class="entry">
        <a href="http://127.0.0.1/herman/viewselector?name=sleeping"
           title="Sleeping bear">Sleeping bear</a>
      </li>
      <li class="entry">
        <a href="http://127.0.0.1/herman/viewselector?name=polarfur"
           title="Polar bear">Polar bear</a>
      </li>
    </ul>
  </dd>
</dl>

>>> logout()

>>> login('zope.mgr')
>>> menu.update()
>>> print menu.render()
<dl id="selectable-views" class="additional-actions">
  <dt>Content display</dt>
  <dd>
    <ul class="menu">
      <li class="entry">
        <a href="http://127.0.0.1/herman/viewselector?name=sleeping"
           title="Sleeping bear">Sleeping bear</a>
      </li>
      <li class="entry">
        <a href="http://127.0.0.1/herman/viewselector?name=polarfur"
           title="Polar bear">Polar bear</a>
      </li>
      <li class="entry">
        <a href="http://127.0.0.1/herman/viewselector?name=springfur"
           title="Spring bear">Spring bear</a>
      </li>
    </ul>
  </dd>
</dl>

>>> logout()

>>> herman.selected_view
u'nothing'

>>> request = TestRequest(form={'name': u'polarfur'})
>>> handler = getMultiAdapter((herman, request), name="viewselector")
>>> handler
<dolmen.app.viewselector.select.ApplyView ...>

>>> login('zope.mgr', request)
>>> handler()
'http://127.0.0.1/herman'

>>> herman.selected_view
u'polarfur'

Changes