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".

>>> from zope.component.hooks import getSite
>>> site = getSite()
>>> herman = site['herman'] = Bear()

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.layout import Page

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

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

>>> class SpringFur(Page):
...   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
>>> 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 view 'viewselector', registered for an IViewSelector content is the component that effectively changes the selected_view attribute to the clicked value.

Let's simulate a click to test that view. The current value of the selected_view attribute is inconsistant:

>>> herman.selected_view
u'nothing'

We want it changed to something existing, like the PolarFur view:

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

Logged in as an admin user, we can apply the selected view:

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

The view redirects you to the base view of the content. The value is now changed:

>>> herman.selected_view
u'polarfur'

Changes